Critique of Pure Reason

Introduction to the Critique of Pure Reason

Immanuel Kant’s book, the Critique of Pure Reason, is a very important and hugely influential work in Western philosophy. Kant published it in 1781, when he was 57. He updated it significantly for a second edition six years later.

This book was a major achievement for Kant. It brought together ideas he had been working on privately for thirty years. It also marked the beginning of almost twenty more years where his philosophical thinking developed quickly and became very public. For over 200 years, scholars have studied this book closely. Creative philosophers continue to find inspiration in its ideas. Telling the full story of the Critique’s influence would mean writing the entire history of philosophy after Kant, which is not our goal here.

This introduction will do two things:

1. First, it will summarize the structure and main arguments of the Critique of Pure Reason.
2. Second, it will describe how Kant developed the ideas for the book, from his earliest writings on metaphysics in 1755 to the Critique’s first publication in 1781 and its revision in 1787.

I. THE ARGUMENT OF THE CRITIQUE

The Strategy of the Critique

Kant once wrote about two things that filled him with constant wonder: “the starry heavens above me and the moral law within me.” This idea captures the spirit of much of his work, especially the Critique of Pure Reason.

Throughout his career, Kant had two main goals:

1. Understanding the Universe: He wanted to solve some of the biggest scientific debates of his time. He aimed to establish the basic principles for knowing about the world, like understanding the “starry heavens.”
2. Understanding Human Freedom and Morality: He also wanted to show that human freedom is real and compatible with modern science. He believed freedom is essential for morality and is the ultimate value that the moral law helps us achieve.

The Critique of Pure Reason was Kant’s major attempt to provide a solid foundation for both modern science and human freedom.

However, the book is quite complex. This isn’t just because Kant’s own ideas are deep. It’s also because he was arguing against several other viewpoints popular in philosophy at the time, particularly during the German Enlightenment.

To make space for his own ideas about science and human freedom, Kant felt he had to challenge traditional metaphysics. For him, this was mainly the philosophy of Christian Wolff and his followers, like Alexander Gottlieb Baumgarten. Kant called their approach dogmatism. He compared dogmatism to a tyrannical government – unpredictable, based on mere opinion, full of internal conflict, unstable, and therefore deserving of criticism from thoughtful people.

Kant also wanted to separate his own critical approach from other ways of rejecting this old-style metaphysics. He believed these other ways were also harmful to reason. These included:

• Skepticism: This is the view Kant believed David Hume represented. Skeptics doubt whether we can truly know anything for certain.
• Empiricism: This view, famously described by John Locke, claims that all knowledge comes only from our individual experiences.
• Indifferentism: This was the attitude of people who didn’t reject big metaphysical ideas (like God’s existence or the soul’s immortality) outright. However, they rejected any attempt to argue for these ideas systematically or with strong proof. These “popular philosophers” often agreed with the dogmatists on the big questions. But they weren’t convinced by the complicated arguments of the dogmatists. Instead, they thought that important life beliefs simply come from “healthy understanding” or common sense.

So, while Kant criticized and tried to limit traditional metaphysics, he also wanted to defend one of its core claims. Against the empiricists, he argued that we can have universal and necessary knowledge. Kant called this a priori knowledge – knowledge that doesn’t come from any particular experience. He believed that knowledge based only on experience (which he called a posteriori knowledge) could never be truly universal or necessarily true.

Kant also wanted to defend metaphysics as a science.

• Against skeptics, who said its arguments weren’t strong enough.
• Against “common sense” thinkers, who saw its detailed arguments as overly complicated and unnecessary.

Kant used comparisons to describe these different groups.

• He saw dogmatic metaphysicians as defenders of a tyranny.
• He likened skeptics to nomads who hate any stable society and are always ready to tear things down.
• He compared followers of Locke (empiricists) to people who would spread false and demeaning stories about the ruling family.
• He accused those who were indifferent to metaphysical questions of being secret dogmatists. They were like people who complain about a corrupt government but don’t actually have any independent beliefs themselves.

Kant’s goal was complex. He needed to:

1. Show the flaws in traditional metaphysics.
2. Replace it with his own scientific metaphysics. This new metaphysics would define what we can know with certainty (a priori). Importantly, it would also limit this knowledge to what is necessary for everyday experience and science.

So, Kant had a difficult task. He had to challenge the dogmatists but still argue that metaphysics could be a science (which skeptics denied) and that it was a necessary field of study (which indifferentists denied).

This meant Kant was fighting on several fronts:

• He had to show that many traditional metaphysical questions simply cannot be answered by human reason. This argued against both the dogmatists (who thought they could answer them) and some empiricists.
• He also had to defend some ideas that were part of the positions he was attacking. For example, he defended the idea that we can have a priori knowledge of the basic principles of science against both empiricists and skeptics.
• He wanted to convince the indifferentists that a science of metaphysics is important.
• However, he also agreed with part of the indifferentists’ view. He thought that for some of the most important, unanswerable metaphysical questions—like God, freedom, and immortality—we can rely on a kind of common-sense belief because these ideas are essential to our moral lives.

The Structure of the Critique

This ambitious plan led to the very complex structure and arguments of the Critique of Pure Reason. Many readers find the book’s detailed organization, or “architectonic,” a roadblock to understanding it. However, knowing a little about where the main divisions of the book came from can help make its contents clearer.

Even though Kant’s ideas were highly original, he actually borrowed much of the book’s structure from existing models.

After the preface and introduction, the Critique is split into two main parts:

1. Doctrine of Elements: This is where Kant lays out his fundamental theory of a priori knowledge – what we can know independent of experience – and what its limits are.
2. Doctrine of Method: Here, Kant reflects on what his theory means for how philosophy should be done. He discusses the differences between mathematical proofs and philosophical arguments, and between thinking about facts (theoretical reasoning) and thinking about morality (practical reasoning). He also contrasts his own critical method with dogmatic, empirical, and skeptical approaches to philosophy.

This two-part division was adapted from German logic textbooks, which commonly distinguished between “general logic” and “special” or applied logic.

The Doctrine of Elements is itself divided into two main parts (though they are very different in length):

1. Transcendental Aesthetic: This section discusses how our basic ways of sensing the world – specifically space and time – contribute to our knowledge before any specific experience.
   • Kant borrowed the term “aesthetic” from the philosopher Baumgarten. Baumgarten used it for the science of “lower” or sensory knowledge, as opposed to logic, the science of “higher” or conceptual knowledge. However, Kant didn’t agree with Baumgarten that there could be a science of taste (what we now call aesthetics). Instead, he used the term for his theory about how the forms of our senses (space and time) contribute to all knowledge.
2. Transcendental Logic: This section discusses how our intellect, or mind, contributes to knowledge before experience. It covers both correct (genuine) and incorrect (spurious) contributions.

Before dividing the “Transcendental Logic,” Kant briefly explains the difference between:

• General logic: The basic science of how thought works, no matter what it’s thinking about.
• Transcendental logic: The science of the basic ways we must think about objects in order to understand them.

Then, Kant splits the Transcendental Logic into two main divisions:

1. Transcendental Analytic: This part explains the positive role of our understanding. It shows how our understanding, working together with our senses, creates the conditions that make experience and knowledge possible. This part is further divided into two books:
   • Analytic of Concepts: This argues that certain pure concepts of the understanding, which Kant calls the categories, are universally valid and necessary. Examples of categories include “substance” (the idea of a thing that persists) and “causation” (the idea of cause and effect).
   • Analytic of Principles: This argues for the validity of fundamental principles we use when making judgments about the world using these categories. Examples include the principle that substance is always conserved (doesn’t disappear) and that every event has a cause.
2. Transcendental Dialectic: This part deals with the errors that happen when our reason tries to work independently of our senses. It examines how reason attempts to gain deep metaphysical insights into “things as they are in themselves” and why this fails. The Transcendental Dialectic also has two books:
   • On the Concepts of Pure Reason: This explains how pure reason creates ideas about things that are beyond our possible experience, such as the soul, the world as a complete whole, and God.
   • On the Dialectical Inferences of Pure Reason: This part shows how reason tries (and fails) to prove that these ideas are real. It does this by taking ways of arguing that are valid within the limits of our senses and incorrectly applying them beyond those limits.

It’s interesting to note how Kant uses a traditional structure from logic textbooks. These textbooks often had three parts: concepts, judgments, and inferences.

• Kant’s Transcendental Analytic (with its “Analytic of Concepts” and “Analytic of Principles”) shows how concepts from our pure understanding, when applied to what our senses give us (space and time), lead to sound principles for making judgments. This forms the core of Kant’s own “critical” metaphysics.
• The main part of the Transcendental Dialectic (“Dialectical Inferences of Pure Reason”) shows how attempting to make inferences using pure reason alone, without respecting the limits of our senses, only leads to metaphysical illusions.

The section on these misleading inferences (“Dialectical Inferences of Pure Reason”) is further divided into three parts. Each part exposes flawed metaphysical arguments about specific topics:

1. The Paralogisms of Pure Reason: Criticizes faulty arguments about the nature of the soul.
2. The Antinomy of Pure Reason: Criticizes contradictory arguments about the universe as a whole (for example, its size or whether it had a beginning).
3. The Ideal of Pure Reason: Criticizes faulty arguments for the existence of God.

These divisions also relate to how earlier philosophers like Wolff and Baumgarten structured metaphysics. They divided it into:

• “General metaphysics” (also called “ontology,” the study of being itself).
• “Special metaphysics,” which included:
  • Rational psychology (about the soul).
  • Rational cosmology (about the world).
  • Rational theology (about God).

Kant effectively replaces their “ontology” with the positive teachings of his own Transcendental Analytic. Then, in the Transcendental Dialectic, he criticizes their “special metaphysics” by showing the flaws in trying to understand the soul, the world, and God using pure reason alone.

Finally, the Doctrine of Method is where Kant discusses the consequences of his critique of traditional metaphysics and his own reconstruction of parts of it. This part has four chapters:

1. The Discipline of Pure Reason: This is a detailed section where Kant compares mathematical proof with philosophical argument. He also provides important explanations of his own new critical method, which he calls the “transcendental” method.
2. The Canon of Pure Reason: This is another detailed section. Here, Kant sets the stage for his later work on moral philosophy. He contrasts the methods of theoretical philosophy (concerned with what we can know) with practical philosophy (concerned with what we should do). He also first outlines a key argument that appears in all three of his Critiques: that practical reason (moral reasoning) can justify beliefs in God, freedom, and the immortality of the soul, even though theoretical reason (scientific or factual reasoning) can never give us actual knowledge of these things.
3. The Architectonic of Pure Reason: This chapter reviews, in a systematic way, the differences between Kant’s own critical philosophical method and the methods of the dogmatists, empiricists, and skeptics he discussed earlier.
4. The History of Pure Reason: This chapter does something similar to the “Architectonic,” but from a historical perspective. Kant wasn’t very interested in the history of philosophy as a field of study for its own sake. However, in these few pages, he presented the history of modern philosophy as a journey where his own critical philosophy overcame the limitations of both empiricism (knowledge only from experience) and rationalism (knowledge primarily from reason). This way of looking at philosophy history is still influential today, although we now also consider the many philosophers who came after Kant.

Now that we’ve looked at how the Critique of Pure Reason is organized, let’s briefly summarize what it says.

The “Introduction”: What is Transcendental Philosophy?

Even though a major part of Kant’s project is to criticize dogmatic metaphysics (the old, speculative philosophy), the Critique actually starts by presenting Kant’s positive ideas about the elements of human knowledge that come from our own minds, known as a priori elements.

In his introduction to the Critique, Kant argues that our knowledge—whether in mathematics, physics, or everyday life—depends on certain kinds of judgments. He says these judgments are:

• Synthetic, not analytic.
  • Analytic judgments merely clarify what is already contained in a concept. For example, “All bachelors are unmarried men” is analytic because “unmarried man” is part of the definition of “bachelor.” You don’t add new information.
  • Synthetic judgments, however, do add new information that isn’t already in the concept. For example, “All events have a cause” (Kant believed this was synthetic).
• And, crucially, some of these synthetic judgments are also a priori.
  • A priori means they are known independently of any particular experience. We know them to be universally true and necessary, not just based on a few observations. No amount of specific experiences could ever prove such universal and necessary truths.

Kant states that the most important question for pure reason is: How are synthetic a priori judgments possible? To answer this, he proposes an entirely new science.

This new science, which Kant calls transcendental philosophy, is different.

• It doesn’t directly study the objects we experience in the world.
• Instead, it investigates the conditions that make our experience of objects possible in the first place. It does this by examining the mental tools or capacities we need to have any knowledge of objects at all.

Kant agreed with Locke that we have no innate knowledge – that is, we aren’t born with specific ideas or propositions already in our minds. However, Kant said that experience is not just a passive reception of information from the outside world. Experience is a product of two things:

1. External objects affecting our senses.
2. The operations of our own minds (our cognitive faculties) as they process these effects.

Kant’s key claim is that we can have pure or a priori knowledge of the contributions our own minds make to experience. This isn’t knowledge of external objects themselves, but knowledge of how our faculties structure and organize experience.

Kant divides our cognitive capacities (our mind’s abilities) into two main types:

1. Sensibility: This is our capacity to receive information from the world when external objects affect us. It provides us with sensations. Through sensibility, objects are “given” to us in what Kant calls empirical intuition. Sensibility is a receptive faculty – it receives data.
2. Understanding: This is our active faculty. It takes the data received through sensibility and relates it by thinking about it under concepts. The understanding is what allows us to form judgments about objects.

As mentioned earlier, this fundamental division between sensibility and understanding forms the basis for the main parts of Kant’s “Doctrine of Elements”:

• The Transcendental Aesthetic deals with sensibility and its pure forms (space and time).
• The Transcendental Logic deals with the operations of understanding and judgment, as well as the activities of theoretical reason – both its legitimate uses and its misuses.

The “Transcendental Aesthetic”: Space, Time, and How We Sense Things

The “Transcendental Aesthetic” is a short but powerful section in Kant’s Critique. Though only about 30-40 pages, it presents remarkable, even revolutionary, ideas. These ideas direct the rest of the book and have been a major focus of study for over 200 years.

In this part, Kant tries to do something important:

• He wants to figure out exactly what our ability to sense things (our sensibility) contributes to our knowledge.
• He wants to separate this from what the objects themselves (which affect our senses) contribute.

Kant’s main argument here is about space and time. He says:

• Space and time are pure forms of all intuition. This means they are the basic structures our own minds (our faculty of sensibility) use to organize any sensory information we receive.
• They don’t exist as independent things “out there,” nor are they just properties of objects themselves.
• Because space and time come from our own minds, we can have a priori knowledge of them – knowledge that is certain and doesn’t depend on any particular experience.

This idea was Kant’s solution to a long-running debate about space and time:

• Newtonians thought space and time were like huge, empty containers that objects existed within, independent of those objects.
• Leibnizians thought space and time were just systems of relationships between objects, created by our concepts based on how things are related.

Kant offered a new alternative:

• Space and time are not independent beings (as Newton thought).
• They are not properties of things as those things might be “in themselves” (which Leibniz’s view might imply).
• Instead, space and time are forms of our sensibility. They are the fundamental ways we humans experience any object. They are the conditions that make it possible for us to experience objects at all.

Kant believed his view was better for two main reasons:

1. It explains why space and time seem to be fundamental to all our experiences. We experience them as single, infinite wholes. Newton tried to explain this with an awkward idea of space and time being God’s “sensory organ” (sensorium dei), which Kant found problematic.
2. It explains how mathematical truths about space and time (like in geometry) can be both synthetic (they add new information, not just analyze concepts) and a priori (we know them with certainty, without needing specific experiences). Leibniz’s view, which saw space and time as derived from objects, couldn’t properly explain the certainty of mathematics.

Kant’s idea that space and time are pure forms of our intuition leads to a striking conclusion:

• Space and time are empirically real. This means that in our everyday experience, space and time are perfectly real. Objects truly are located in space and events really do happen in time for us.
• However, space and time are transcendentally ideal. This means that from a deeper, philosophical viewpoint (the “transcendental” view), space and time are not features of how things are “in themselves,” completely independent of us. Instead, they are structures of our human way of sensing. The same goes for the objects we perceive within space and time.

This leads to Kant’s famous doctrine of transcendental idealism. In simple terms, this means:

• We can only know things as they appear to us (as phenomena). These appearances are shaped by the conditions of our sensibility (space and time).
• We cannot know things “as they are in themselves” (noumena), that is, as they might be completely independent of how our minds are structured to perceive them.

Kant uses transcendental idealism throughout the Critique of Pure Reason (and his later Critiques) in several ways:

• Positively: For example, in the “Transcendental Aesthetic” and later in the “Discipline of Pure Reason,” it helps explain how we can have synthetic a priori knowledge in mathematics. Mathematics deals with space and time, which are these pure forms of our intuition.
• Negatively: For example, in the “Transcendental Dialectic,” it serves to limit the reach of our knowledge. It shows that our knowledge is restricted to appearances given to our senses. We cannot gain knowledge of “things in themselves” as realities existing beyond the constitution of our minds.

The “Transcendental Analytic”: How Our Understanding Shapes Knowledge

The “Transcendental Logic” is the longest and most detailed part of the Critique. It has two main divisions:

1. The Transcendental Analytic: This is the constructive, or positive, part. It explores how our understanding is a source of a priori concepts (concepts that don’t come from experience). These concepts, when combined with the forms of intuition (space and time from the “Transcendental Aesthetic”), provide us with a priori knowledge.
2. The Transcendental Dialectic: This part is mostly destructive, or critical. It investigates our faculty of reason. It shows how reason, when it tries to go beyond experience, can lead to illusory arguments and false metaphysical “sciences.” However, Kant also shows that reason can provide valuable guiding principles for scientific inquiry and for practical (moral) life.

As we saw before, the Transcendental Analytic itself is divided into two “books”:

• Book I: Analytic of Concepts: This deals with the pure concepts that originate in our understanding.
• Book II: Analytic of Principles: This concerns the principles of understanding that arise when we apply these pure concepts to what we sense (our intuitions).

In the Analytic of Concepts, Kant argues that our understanding is the source of certain fundamental concepts.

• These concepts are a priori (not learned from experience).
• They are absolutely necessary conditions for us to have any experience of the world at all.

Kant identifies twelve of these basic concepts, which he calls the categories.

• The categories are fundamental ways of thinking about any object in general. They are like basic forms for any specific concepts of objects we might have.
• Together with the a priori forms of intuition (space and time), the categories are the foundation of all synthetic a priori knowledge (knowledge that adds new information and is known with certainty, independent of particular experiences).

Kant attempts to discover these categories in a section he later called the metaphysical deduction of the categories.

• He derives these twelve categories from a table of twelve basic logical functions of judgment. These are the essential, logically significant ways in which any judgment (any statement we make) can be structured.
• Kant’s idea is that if there are fundamental ways all judgments are structured, there must be corresponding fundamental ways our minds form concepts of objects, so that our judgments can actually be about those objects.

There are four main groups of logical features for judgments, and Kant believed each group has three options:

1. Quantity: The scope of the judgment.
   • Universal (e.g., “All S is P”)
   • Particular (e.g., “Some S is P”)
   • Singular (e.g., “This S is P”)
2. Quality: Whether the judgment affirms or denies something.
   • Affirmative (e.g., “S is P”)
   • Negative (e.g., “S is not P”)
   • Infinite (e.g., “S is non-P”)
3. Relation: The type of logical connection asserted.
   • Categorical (e.g., “S is P” – a direct relation)
   • Hypothetical (e.g., “If S, then P” – a conditional relation)
   • Disjunctive (e.g., “S is either P or Q” – a relation of alternatives)
4. Modality: The way the judgment claims truth.
   • Problematic (e.g., “S may be P” – possible)
   • Assertoric (e.g., “S is P” – actual)
   • Apodictic (e.g., “S must be P” – necessary)

Corresponding to these twelve logical forms of judgment, Kant argues there are twelve fundamental categories for thinking about the quantity, quality, relation, and modality of objects. However, Kant’s claim that there are exactly twelve logical functions and exactly twelve corresponding categories has been a point of discussion and controversy ever since he first made it.

Even if the “metaphysical deduction” successfully shows that we possess certain a priori concepts (the categories), Kant faced a bigger challenge. He needed to prove that these concepts apply universally and necessarily to all the objects we encounter in our experience.

This is the goal of the Transcendental Deduction of the Categories.

• Kant himself said this chapter was the most difficult one for him to write.
• He rewrote it almost completely for the second edition of the Critique, after exploring the ideas in other works published between the two editions.

The core argument of the Transcendental Deduction (in both editions of the Critique) centers on this idea:

• For our experiences to be our experiences—coherent and belonging to a single, self-aware subject—they must be unified. Kant calls this the transcendental unity of apperception. You can think of this as the basic fact that an “I think” must be able to accompany all my thoughts and perceptions for them to be mine.
• This unity of experience is only possible if the raw data coming from our senses (our intuitions) is actively combined and structured by our minds so that it presents us with recognizable objects.
• This structuring, this synthesis of sensory data into objects, happens when we think about that data through the categories.

Therefore, Kant concludes, the categories must apply to objects.

• They don’t apply because objects somehow create these concepts in us.
• Rather, the categories themselves are the necessary rules or conditions that our minds use to represent any possible object of experience. They make experience, as we know it, possible.

However, the precise meaning of the “unity of apperception” and its exact relationship to how we represent objects are complex and have been debated by philosophers for centuries.

The “Analytic of Principles”: Applying Concepts to Experience

Even if the Transcendental Deduction shows that the categories apply to all possible sensory data (or “manifolds of intuition,” in Kant’s terms), it does so in a general and abstract way. It doesn’t explain how each specific category applies to objects in experience, nor does it show that all of them must be applied.

This is Kant’s task in Book II of the “Transcendental Analytic,” called the Analytic of Principles. This book has three main chapters:

1. The Schematism of the Pure Concepts of the Understanding:
   • This chapter explains how the purely logical categories (from the metaphysical deduction) can be made applicable to the actual data we receive through our senses. It bridges the gap between abstract concepts and concrete sensations.
2. The System of All Principles of Pure Understanding:
   • Here, Kant demonstrates specific principles of judgment. These principles aim to show that all the categories must be applied in our experience.
   • Some scholars believe the arguments in this chapter might even be strong enough to prove the objective validity of the categories independently of the (very complex) Transcendental Deduction.
3. On the Ground of the Distinction of All Objects in General into Phenomena and Noumena:
   • This chapter draws out the important consequences of the previous two.
   • It argues that because the categories only have a definite use when applied to data given in space and time (which are forms of our sensibility), and because space and time themselves are “transcendentally ideal” (forms of our minds, not properties of things in themselves), it follows that:
     • The categories also only have a definite cognitive use when applied to appearances (phenomena).
     • Therefore, while we might be able to think of things as they are in themselves (noumena) using the categories, we can never know them as such.

In The Schematism, Kant addresses a key problem: the categories are pure concepts of the understanding, while the objects we experience are given to us through our senses in space and time. How can these abstract concepts connect to concrete sensory input?

• Kant argues this connection is made through a transcendental schema for each category.
• A schema is a kind of rule or procedure, a product of imagination, that links a pure concept to a specific form or relation in our sensory experience (intuition). It translates the logical meaning of a category into a rule for how it applies to what we sense.
• Kant particularly emphasizes temporal schemata – schemata related to time. This is because time is the form of all our sensible intuitions (both inner experiences like thoughts and outer experiences of objects), while space is only the form of outer intuitions.
• Example: The logical category of “ground and consequence” (the basis of causality) is schematized as rule-governed temporal succession. The concept of a cause (as distinct from just a logical ground) becomes “something real, such that whenever it is present, something else always follows it in time according to a rule.”
• Kant later clarifies (especially in the second edition) that even though the basic content of these schemata can be explained in terms of time, actually using these schemata often depends on making judgments about the spatial properties and relations of objects.

So, the overall argument of the “Analytic of Principles” is that the categories must be used to gain knowledge of objects in space and time, and indeed, they can only be used in this way. The principles that express this universal and necessary application of the categories to objects in space and time are precisely the synthetic a priori judgments that Kant’s new “critical” metaphysics aims to identify and prove.

In the second chapter, The System of All Principles, Kant organizes the principles of pure understanding into four groups, matching the four groups of categories (Quantity, Quality, Relation, Modality).

For the first two groups (Quantity and Quality), Kant provides Mathematical Principles. These are meant to ensure that mathematics can be applied to objects we experience.

1. Axioms of Intuition (corresponding to the categories of Quantity):
   • This principle guarantees that mathematics dealing with extensive magnitudes applies to empirical objects. Extensive magnitudes are things where the whole is measured by adding up its discrete parts (like a line is made of points, an area of smaller areas, or a duration of smaller time units).
   • This applies because empirical objects are given to us in space and time, and space and time are themselves extensive magnitudes.
   • A wider implication is that our ability to use logical quantifiers like “one,” “some,” or “all” when talking about experience depends on our ability to divide what we experience into distinct spatiotemporal regions.
2. Anticipations of Perception (corresponding to the categories of Quality):
   • This principle guarantees that mathematics dealing with intensive magnitudes applies to the “real in space.” Intensive magnitudes are qualities that have degrees, but are not made up of summed parts (like the brightness of a light, the warmth of an object, or the strength of a force).
   • Properties like color, heat, or forces (like weight) must exist in a continuous range of degrees. This is because our sensations of them can vary continuously.
   • Kant argues that using logical functions of affirmation (“yes, this quality is present”) and negation (“no, this quality is not present”) in experience depends on sensations having these continuously varying degrees. This connection between the categories of Quality and the mathematics of intensive magnitudes is a synthetic a priori judgment – it’s not something we could know just by analyzing the logical meaning of the categories themselves.

Next, Kant moves from “mathematical” principles to Dynamical Principles. These relate to the categories of “Relation” and concern the necessary connections among things as they are given in space and time. The section discussing these is called the Analogies of Experience, and many scholars consider it one of the most important parts of the Critique.

1. First Analogy (Principle of Permanence of Substance):
   • Kant argues that because time itself is a unified whole, any change we observe must be understood as an alteration of the states of some underlying substance.
   • This underlying substance must itself be permanent; its existence and total quantity must remain unchanged or conserved through all changes of its states.
2. Second Analogy (Principle of Succession in Time, according to the Law of Causality):
   • To make reliable judgments about the objective order of events (how things actually happened one after another), as opposed to just the subjective order of our own perceptions (which can be arbitrary), every objective change must follow a necessary rule of succession.
   • This necessary rule is a causal law: every event must have a cause that makes it happen.
   • This argument is generally seen as Kant’s answer to David Hume’s skeptical doubts about whether we can truly know cause and effect.
3. Third Analogy (Principle of Coexistence, according to the Law of Reciprocity or Community):
   • To make reliable judgments that different objects (or different states of substances) located in different parts of space exist at the same time (simultaneously), these objects must be in a state of mutual causal interaction or community. They must be able to affect each other.
   • This argument is partly aimed at refuting Leibniz’s view (his “monadology”) that individual substances (monads) do not genuinely interact with each other.

The Second Analogy, in particular – what exactly Kant intended to prove with it and how his proof works – has been a subject of much scholarly debate. This debate is almost as intense as the philosophical question of whether Kant’s reply to Hume on causality is ultimately successful.

The final section of the “System of Principles” deals with the modal categories (possibility, actuality, necessity) and is called the Postulates of Empirical Thought.

• In the first edition of the Critique, this section provides conditions for how we use these modal concepts in experience. Kant argues that our definite use of “possibility” and “necessity” is actually limited to the realm of the “actual” – that which is actually given to us in experience.

• In the second edition, Kant added a famous new argument here called the Refutation of Idealism.

  • This argument tries to show that the very possibility of our being conscious of ourselves (our own existence in time) presupposes the existence of an external world of objects.
  • These objects are not just represented by us as being spatially outside us; they must also be conceived of as existing independently of our subjective thoughts or representations of them.
  • While the full implications of this argument are still debated, it seems to support Kant’s claim (made elsewhere, for instance, in his Prolegomena to Any Future Metaphysics) that his transcendental idealism is a special kind – a “critical” or “formal” idealism.
  • Unlike some other forms of idealism, Kant’s view, while holding that space and time are subjective forms of our intuition, does not deny the real existence of objects distinct from ourselves that we represent as being in space and time.

In the third and final chapter of the “Analytic of Principles,” titled On the Ground of the Distinction of All Objects in General into Phenomena and Noumena, Kant reinforces a crucial consequence of his arguments.

• Because the categories must always be applied to sensory data (intuitions) to yield actual knowledge,
• And because this sensory data is structured by our transcendentally ideal forms of space and time,
• It follows that the categories can only give us knowledge of things as they appear to us through our sensibility. Kant calls these appearances phenomena (literally, “things that appear”).

Kant also considers things as they might be conceived by pure understanding, independently of being given to our senses. The Greek word for intellect or pure thought is noûs, and Kant calls such purely thinkable entities noumena (literally, “things that are thought”).

• However, he concludes that we can never know these noumena as non-sensible entities. We can think them, but not know them.
• The meaning of “phenomena” is fairly straightforward. But “noumena” is more complex. It doesn’t just mean “things as they are in themselves, independent of how they appear to us.” It literally means something more like “things as they are understood by pure thought.”
• Yet, Kant seems to deny that human understanding is capable of comprehending things in this latter way – as objects of pure thought detached from the conditions of our sensory experience.

So, Kant says we can talk about noumena (things as they might be in themselves) only in a “negative sense.” This means we can think of them as things that are not objects of our senses, existing independently of how we perceive them. But we cannot talk about noumena in a “positive sense,” which would mean knowing them directly through pure reason alone.

A fundamental point of the Critique is that we never get knowledge of things through pure reason by itself. We only gain knowledge when our minds apply their basic concepts (the categories) to information from our senses (which is structured by space and time).

At this stage in the Critique, Kant has finished most of his positive, or constructive, project. He has shown how we can have certain knowledge that adds new information (synthetic a priori principles) about the world we experience. This knowledge comes from applying the categories to sensory data, which is already structured by the pure forms of intuition (space and time).

The next major part of Kant’s argument is to show a critical point: traditional metaphysics is largely made up of illusions. These illusions happen when reason tries to gain knowledge about ultimate things (like the soul, the world as a whole, and God) “as they are in themselves.” This happens when reason ignores the limits of what our senses can tell us.

The main discussion of these illusions is in the part of the Critique called the Transcendental Dialectic. However, Kant starts this critical task in an interesting appendix that finishes the “Transcendental Analytic.” This appendix is titled the Amphiboly of Concepts of Reflection.

• In this section, Kant criticizes the philosophy of Leibniz, particularly his theory of monads (simple, fundamental substances).
• Kant argues that Leibniz made a kind of confusion, which Kant calls an “amphiboly.” Leibniz mistook features of how we think about things for features of the things themselves.
• Specifically, Leibniz looked at concepts we use for comparison or reflection—like “same” and “different,” or “inner” and “outer.” Kant says these general comparison concepts are never applied directly to objects. We only apply them to objects by using other, more specific concepts that actually describe the objects. Leibniz, however, treated these comparison concepts as if they were direct properties of the objects.
• By showing this confusion, Kant rejects how Leibniz and another philosopher, Wolff, understood basic metaphysical concepts like “essence,” “identity,” and “possibility.”
• Kant reinforces his own view: to say something is really possible in the world we experience, it’s not enough for it to be logically understandable or free of contradictions. It must also be connected to sensible conditions – there must be a way it could be given in experience.

The “Transcendental Dialectic”: Exposing Illusions and Finding Value

The “Transcendental Dialectic” is the second major division of the “Transcendental Logic.” It takes on the main “destructive” task of the Critique of Pure Reason. This task is so central that it gives the Critique its name: it’s a critique of pure reason itself, showing its limits. This section aims to:

• Discredit dogmatism (metaphysics that speculates beyond experience).
• Clearly show the proper limits of metaphysics.

The “Transcendental Analytic” already prepared for this. It argued that we can only establish certain, informative principles (synthetic a priori principles) if they apply within the limited area of what we can sense and experience.

But Kant has a dual aim in the “Dialectic”:

1. He wants to show why metaphysics fails when it tries to go beyond the boundaries of possible experience.
2. At the same time, he wants to show that the fundamental questions that metaphysics wrestles with—about the soul, the world as a whole, God—are questions that human reason cannot avoid asking. They are inevitable.
   • The arguments of traditional metaphysics might be deceptive. But Kant believes we shouldn’t just dismiss them with contempt, as skeptics often do.
   • These metaphysical ideas tempt us for real reasons, reasons found in the very nature of human reason.
   • If we properly understand why reason generates these ideas, we can actually put them to good use. They can help us in our search for knowledge and in understanding morality.

This argument by Kant leads to two important theories:

• The regulative use of the ideas of reason: In science, these grand ideas (like the idea of a perfectly unified natural system, or the idea of the soul, or God) can serve as valuable guides. We can’t prove these ideas correspond to real entities. But they can direct our research and help us organize our knowledge. Kant first mentions this in an appendix to the “Transcendental Dialectic” and develops it more in his later book, the Critique of Judgment.
• The foundation of morality in the practical use of pure reason: Our moral life requires us to believe certain things (like human freedom, God, and immortality). Kant argues that pure reason, in its practical (moral) function, can justify these beliefs, even if theoretical (scientific) reason cannot prove them as facts. He first outlines this in the “Doctrine of Method” section of the Critique of Pure Reason and explains it more fully in later works, especially the Groundwork of the Metaphysics of Morals and the Critique of Practical Reason.

The type of metaphysics Kant was often arguing against (the Leibnizian-Wolffian tradition, as found in Alexander Baumgarten’s textbook Metaphysica, which Kant used for his own lectures) was typically divided into four parts:

1. Ontology: The study of being or existence in general.
2. Psychology: The study of the soul.
3. Cosmology: The study of the world as a whole.
4. Theology: The study of God.

Kant’s “Transcendental Aesthetic” and “Transcendental Analytic” are his critical replacement for traditional ontology. They offer a new understanding of how we can know objects within our experience.

The Transcendental Dialectic, however, focuses on the other three parts of that old system. Kant argues that rational psychology, rational cosmology, and rational theology are pseudo-sciences. They are built on unavoidable illusions that happen when human reason tries to stretch its reach beyond the limits of what our senses can experience.

Kant doesn’t just treat these as outdated historical errors. He tries to show that they are inevitable products of how human reason naturally works. He connects the drive to create these pseudo-sciences with reason’s attempt to find the unconditioned—the ultimate, absolute foundation for things. Reason does this, he suggests, by misapplying the three traditional forms of logical argument (syllogisms: categorical, hypothetical, and disjunctive):

• When reason seeks an unconditioned subject for all our thoughts (using categorical logic), it generates the idea of the soul as a simple, non-empirical substance.
• When reason seeks an unconditioned series of conditions in the world—like a first event in time, an outer limit to space, a simplest substance, or a first cause (using hypothetical logic)—it generates ideas about the world as a whole.
• When reason seeks an unconditioned ground for all possibilities (using disjunctive logic), it derives the idea of a most real being, or God.

Kant’s overall argument is that while these ideas of reason are unavoidable illusions if taken as knowledge of transcendent realities, they are still pseudo-sciences. They must be replaced by forms of inquiry that remain within the limits of what we can experience:

• Rational psychology (about the soul) must give way to empirical psychology (the study of the mind based on experience, which Kant taught in his lectures as “anthropology”).
• Rational cosmology (about the world as a whole) must give way to the metaphysical foundations of natural science (the basic principles of physics, which Kant believed could be derived by applying his categories to experience, combined with the empirical concept of motion).
• Rational theology (attempting to prove God’s existence) must give way to what Kant will later call moral theology. This is the idea that we postulate God and immortality, along with freedom of the will, not as proven facts, but as necessary conditions for the possibility of human morality.

The first book of the “Transcendental Dialectic” therefore explains where these transcendental ideas (like the immortal soul, free will, and God) come from. These are the ideas that dogmatic metaphysics has always been concerned with. Kant even offers a kind of limited defense of these ideas – not as knowledge of real things, but as natural and inevitable products of human reason.

Reason, traditionally seen as our highest mental ability, has two main uses:

1. A logical use: Here, reason simply draws inferences or conclusions from given principles.
2. A real use: Here, reason tries to find ultimate, foundational principles for series of ordinary inferences. For example, it tries to trace a chain of causes and effects back to an uncaused first cause. This “real use” of reason is always searching for the unconditioned – an absolute starting point or complete explanation that doesn’t depend on anything further.

These ideas of ultimate, unconditioned principles are generated a priori (independently of experience) by our faculty of reason. This happens when reason, through chains of logical arguments (syllogistic reasoning), tries to find what is unconditioned for the objects we encounter in experience. It attempts to go beyond the principles of understanding that govern those objects.

In particular, Kant links the main ideas of metaphysics to the three categories of relation (substance, causality, and community) when reason tries to use these categories without respecting the limits of our senses:

• The concept of substance, when pushed to find an ultimate subject, gives rise to the idea of the soul.
• The concept of causation, when pushed to find a complete series of conditions, gives rise to the idea of the world-whole.
• The concept of community (or reciprocal interaction), when pushed to find a common ground for all possibilities, gives rise to the idea of God.

Kant suggests that each of these three relational categories is associated with a specific form of logical inference (syllogism). Reason naturally extends these series of inferences until it arrives at an idea of an unconditioned ground. More directly, when reason attempts to use the relational categories to gain knowledge without the input of sensibility, it directly generates these ideas of an unconditioned subject (soul), an unconditioned series (world-whole), and an unconditioned set of all possibilities (God).

The second, and much larger, book of the “Transcendental Dialectic” is called The Dialectical Inferences of Pure Reason. It explains in great detail how reason falls into these errors. This book is divided into three main sections, each diagnosing the errors of a specific branch of traditional rationalist metaphysics:

1. The Paralogisms of Pure Reason: Deals with the errors of rational psychology (arguments about the soul).
2. The Antinomy of Pure Reason: Deals with the errors of rational cosmology (arguments about the world as a whole).
3. The Ideal of Pure Reason: Deals with the errors of rational theology (arguments about God).

The Paralogisms: Flawed Arguments About the Soul

Rational psychology is the subject of the “Paralogisms.” “Paralogisms” are deceptive or fallacious (flawed) inferences made by pure reason.

• These arguments incorrectly move from the purely formal features of our self-consciousness (the “I” in “I think” seems to be a single, simple, and enduring subject) to conclusions about the soul as a real thing.
• Rational psychology wrongly concludes that the soul is a real, simple (and therefore indestructible) substance that remains self-identical throughout all our experiences. Kant shows these arguments are invalid.

There were some changes to this section between the first and second editions of the Critique:

• The first edition included a fourth part to the Paralogisms. This part tried to defend the reality of the external world (objects in space) by saying they are just one type of our immediate representations. However, this argument seemed like a weak victory and led some critics to accuse Kant of being an idealist like Bishop Berkeley (who denied the existence of a material world independent of mind).
• In the second edition, Kant replaced this weak argument with the Refutation of Idealism (which we discussed earlier). The Refutation argues more strongly for the real existence of objects in space and time, while still maintaining that space and time themselves are transcendentally ideal (forms of our sensibility).
• The entire chapter on the Paralogisms was rewritten and simplified for the second edition. To replace the old fourth paralogism, Kant added a new argument. He suggested that his distinction between appearances and reality helps to undercut the traditional mind-body problem. Instead of mind and body being two fundamentally different kinds of substances that struggle to interact, Kant opened the possibility that mind and body might simply be different appearances of some single, underlying (though unknown) kind of substance.

The Antinomies: Contradictions About the World

The Antinomy of Pure Reason is the longest and most detailed part of the “Transcendental Dialectic.” It deals with the topics of rational cosmology—the attempt by pure reason to understand the world as a complete whole. (Kant actually once thought that all the errors of metaphysics could be exposed as antinomies.)

In this section, Kant argues that reason’s natural illusions don’t just show up after subtle philosophical mistakes. Instead, they unavoidably lead to actual contradictions. For certain questions about the world as a whole, reason can produce two opposing arguments, and both sides of the contradiction seem plausible and naturally convincing.

Kant argues that unless we accept his transcendental idealist distinction—the difference between appearances (things as we experience them) and things in themselves (things as they might be independently of our minds)—we will be forced to accept sets of mutually incompatible arguments. These include:

1. First Antinomy (about the world’s beginning and limits):
   • Thesis: The world must have a beginning in time and be limited in space.
   • Antithesis: The world cannot have a beginning in time and cannot be limited in space.
2. Second Antinomy (about simple substances):
   • Thesis: There must be simple substances (ultimate, indivisible parts).
   • Antithesis: There cannot be any simple substances; everything is infinitely divisible.
3. Third Antinomy (about freedom and natural causality):
   • Thesis: There must be at least one first or uncaused cause (freedom) to explain events.
   • Antithesis: There cannot be any uncaused cause; everything happens according to fixed laws of nature.
4. Fourth Antinomy (about a necessary being):
   • Thesis: There must be a being whose existence is absolutely necessary, either as part of the world or as its ground.
   • Antithesis: There cannot be any such absolutely necessary being.

Kant argues that the only way to resolve these contradictions is to accept that the natural world we experience is a realm of appearances. This world is constructed by our minds applying the categories to sensory information, not a realm of things as they are in themselves.

• For the first two antinomies (which he calls mathematical antinomies because they deal with size, duration, and composition), Kant argues that there is actually no fact of the matter about the total size of the world or whether it’s made of ultimate simple parts.

  • This is because the natural world is never presented to us in experience as a complete whole. We only encounter it progressively, through our ongoing activity of synthesizing (putting together or breaking down) our experiences in space and time.
  • We can always continue this process indefinitely—imagining larger spaces and longer times, or smaller and smaller divisions—but we never reach an absolute beginning or end, nor an ultimate simple part. We also can’t complete an infinite synthesis.
  • Therefore, Kant concludes that both sides of the mathematical antinomies are false. They both mistakenly assume that the world is a thing given independently of our minds, with a definite total size or composition (either finite or infinite) that we could discover.

• For the third and fourth antinomies (which he calls dynamical antinomies because they deal with causation, freedom, and the existence of a necessary being), Kant offers a different solution.

  • Here, he argues that both sides of the contradiction may be true, but in different senses or applying to different realms.
  • The denial of a free (uncaused) cause or a necessary being can be true if we are talking about the natural, sensible world of appearances, which is governed by deterministic laws.
  • The affirmation of a free cause or a necessary being can be true if we are talking about what might exist in a noumenal or supersensible world—a world of things in themselves, beyond our direct experience.

Kant’s thinking about these antinomies was very important for shaping the overall structure and outcome of the “Transcendental Dialectic.” His resolution of the Third Antinomy, which allows for both natural causality (in the world of appearances) and the possibility of freedom (related to the noumenal world), plays a crucial role in his later moral philosophy and his account of how scientific knowledge and moral principles relate to each other.

The Ideal of Pure Reason: Flawed Arguments About God

Rational theology, the third and last of the metaphysical pseudo-sciences, is the topic of the final chapter of the “Transcendental Dialectic.”

• If an idea (in Kant’s special sense) is a pure concept generated by reason (like the idea of “the soul” or “the world-whole”), then an ideal is the concept of an individual thing that is imagined to perfectly embody such an idea of pure reason.
• It might not seem natural to think of an “ideal soul” because we usually imagine many souls.
• However, it is natural (at least in traditions like Judaism and Christianity) to think of the idea of God as the idea of a single, unique being. Thus, for Kant, the idea of God is the Ideal of Pure Reason.

Kant argues that reason inevitably forms the idea of God as an ens realissimum. This Latin term means the “most real being.” It’s the concept of a supreme individual thing that possesses all possible realities or perfections and, because of this, serves as the ultimate ground for all the possibilities that are realized in other, particular things. Kant had explored similar lines of thought almost twenty years before publishing the Critique, in a work called The Only Possible Ground of Proof for a Demonstration of the Existence of God (1763). But now, in the Critique, Kant subjects to intense criticism his own earlier attempt to prove God’s existence as such an ens realissimum. He also criticizes all other traditional attempts to prove God’s existence. He had already criticized some of these proofs in his earliest philosophical writings.

Kant organizes the traditional proofs for God’s existence into three types (without explaining why he limits it to just these three):

1. The ontological proof: This proof is based solely on the concept of God. It argues that the very definition of God (for example, as a supremely perfect being) implies that God must exist. (Philosophers like St. Anselm and Descartes favored versions of this).
2. The cosmological proof: This proof is based on the sheer fact that a world exists. It argues from the existence of contingent beings (things that exist but might not have existed) to the necessity of an ultimate, uncaused ground for their existence. (Favored by Wolff and his followers).
3. The physico-theological proof (also known as the argument from design): This proof is based on the particular features and order of the actual world, especially its apparent purposiveness and design. (Popular among many Enlightenment thinkers, though David Hume had already strongly criticized it).

Kant attacks these proofs one by one:

• He first criticizes the ontological argument. His main objection is that existence is not a real property or predicate that can be part of the definition of a thing. Therefore, existence cannot be considered one of God’s “perfections” from which God’s existence could be logically inferred. Saying “God exists” doesn’t add a new feature to the concept of God; it claims that the concept applies to something real. For Kant, the existence of an object is always something that must be presupposed if we are to make any true statements about its properties; existence itself cannot be proven from the mere concept of the object.

• He then argues that even if the cosmological and physico-theological proofs could establish the existence of some kind of necessary or purposive being (which he doubts they can), they would still fall short. To prove that this being is the supremely perfect Deity (the ens realissimum), these proofs would still need to rely on the success of the ontological proof (to link this necessary being with the concept of supreme perfection).

Since Kant believes the ontological proof is unsound, he concludes that the entire metaphysical project of trying to prove the existence of God—as an object of theoretical knowledge—is hopeless.

The Positive Role of Reason’s Ideas: Guiding Inquiry

The outcome of the “Transcendental Dialectic” might therefore seem entirely negative, as if its only purpose is to tear down traditional metaphysics. However, Kant says this is a misleading conclusion.

In an appendix to the “Dialectic,” Kant begins a kind of rehabilitation of the ideas of traditional metaphysics. He argues that the ideas of reason (like the soul, the world as a whole, and God) can have an important and positive function, especially in guiding natural science, if they are understood regulatively.

To use these ideas “regulatively” means:

• We don’t take them to represent actual metaphysical beings or entities whose reality we can prove.
• Instead, we use them as goals and directions for our inquiries. They mark out pathways for how we should seek knowledge and how we should try to organize the knowledge we acquire.

Here are some examples of this regulative use:

• The idea of a simple soul can stimulate us to search for a unified and coherent understanding in psychology.
• The idea of a complete world-whole can lead us to constantly try to expand the scope of our scientific investigations, to see connections between different areas of study, and to seek ever more comprehensive explanations.
• Above all, the idea of God can be regulatively useful. If we approach the study of the world as if it were the product of a highest intelligence, this can lead us to look for the maximum possible order, purpose, and interconnectedness in nature. This search for systematic unity is beneficial for organizing whatever empirical knowledge we do manage to acquire.

This argument about the regulative use of reason’s ideas is something Kant continues to develop in his later work, the Critique of Judgment. It is one of his first major constructive arguments showing that while reason can be misleading if its ideas are misunderstood, reason, when wisely used, is far from being useless or unnecessary. In fact, its ideas can be indispensable guides.

Kant’s second major positive argument about reason is that its ideas have a deep practical use for guiding our actions and behavior. He begins to develop this argument in the final main part of the Critique, the Doctrine of Method.

The “Doctrine of Method”: How to Use Reason Correctly

The “Doctrine of Method” is the second major division of the Critique of Pure Reason. Readers often overlook this section. This might be because the first part, the “Doctrine of Elements,” is so long, and the arguments covered so far are quite demanding.

However, the “Doctrine of Method” contains some extremely important discussions. In it, Kant reflects on the potential and the limits of his own critical philosophy. He does this by comparing his method with other approaches:

• He compares the method of philosophy with the method of mathematics.
• He compares the method of theoretical philosophy (what we can know) with the method of practical philosophy (what we should do, or morality).
• He compares his own critical method with dogmatic, empirical, and skeptical ways of doing philosophy.

The first chapter of the “Doctrine of Method” is called the Discipline of Pure Reason.

• This chapter provides Kant’s most developed thoughts on the difference between philosophy and mathematics.
  • He argues that both philosophy and mathematics give us synthetic a priori knowledge (knowledge that is new, not just clarifying definitions, and is certain without needing specific experiences).
  • However, mathematics provides definite, specific answers to its problems. This is because mathematics can construct its objects in pure intuition. For example, a geometer can draw or imagine a triangle based on its definition and explore its properties directly.
  • Philosophy, on the other hand, provides only general principles. What philosophy can “construct” are the conditions that make it possible for us to experience objects at all, not particular objects themselves.
• The chapter then offers a strong defense of freedom of public communication and open-mindedness when discussing metaphysical issues.
  • Kant argues that the very existence of reason itself depends on the free exchange of ideas and arguments among thinking beings.
  • This requires that people have the liberty to arrive at their own conclusions honestly and to express those conclusions openly to others.
  • This discussion anticipates Kant’s passionate defense of freedom of thought in his political writings later in the 1790s.
• The chapter concludes with two more topics:
  • A discussion of the different roles that hypotheses play in science versus philosophy.
  • A reflection on his own style of philosophical argument, which he calls transcendental proofs.

The second chapter of the “Doctrine of Method” is the Canon of Pure Reason.

• This chapter contrasts the status of theoretical knowledge (what we can know about the world) with the principles and assumptions of practical reason, or morality.
• In doing so, it provides Kant’s most systematic discussion of moral philosophy before he wrote his famous Groundwork of the Metaphysics of Morals (1785).
• It also contains Kant’s first systematic statement of his argument for rational faith in God based on moral grounds. This is an argument Kant would restate and refine in his next two Critiques and continue to work on for the rest of his life.

The third chapter is the Architectonic of Pure Reason.

• This section continues the discussion comparing philosophy to other forms of knowledge, such as historical knowledge.
• It also further explores the contrast within philosophy between theoretical reason and practical (moral) reason.

The final chapter of the “Doctrine of Method,” and of the entire Critique of Pure Reason, is the History of Pure Reason.

• This chapter clearly positions Kant’s critical philosophy in relation to the competing philosophical approaches that he discussed at the very beginning of the Critique: dogmatism, empiricism, skepticism, and indifferentism.
• Although this section is brief, it has had a significant influence on how later thinkers have understood the history of philosophy.

II. THE MESSAGE OF THE CRITIQUE

The Critique of Pure Reason is a complex and many-sided book. Its overall message and its meaning for the later history of philosophy are not easy to summarize quickly.

Perhaps the most common way of seeing the Critique is as marking out a “third way” in philosophy. This path supposedly combines the strengths of both rationalism (the philosophies of thinkers like Descartes and Leibniz, who emphasized reason as the source of knowledge) and empiricism (the philosophies of thinkers like Locke and Hume, who emphasized experience). This “third way” aims to achieve these strengths while avoiding the pitfalls of each approach. However, this way of reading the Critique, even though Kant himself sometimes hinted at it, depends on a simplified understanding of the history of modern philosophy. At the very least, it doesn’t fully assess the strengths and weaknesses of the philosophers who came before Kant.

A less controversial observation is that the Critique’s main intention is to find a middle way between two extremes:

1. Traditional metaphysics, especially its attempts to support a belief in God with purely rational arguments (a priori arguments).
2. Skepticism, which would undermine the claims of modern natural science as well as the claims of religious metaphysics.

We see this clearly in how Kant defines his critical philosophy against dogmatism, empiricism, skepticism, and indifferentism. He tries to carve out a significant but limited area for theoretical philosophy. This area is distinct from empirical knowledge (gained through science and experience) and from the opinions of common sense. But it excludes the exaggerated claims that had brought traditional metaphysics into disrepute.

In this respect, the Critique of Pure Reason belongs to a major tradition in modern philosophy, starting with Descartes. This tradition tries to provide an a priori philosophical foundation for the methods and general features of a modern scientific view of nature. It does this by examining human mental faculties to see how they are suited for the kind of knowledge of nature that modern science aims to achieve.

At the same time, Kant tries to save something important that he believed the dogmatic metaphysicians could not save. He does this by connecting the claims of religious metaphysics not to the realm of theoretical knowledge, but to the realm of moral practice. In the famous words of the preface to the second edition of the Critique, Kant said he aimed to “limit knowledge in order to make room for faith.”

But Kant tries to achieve all these goals, especially this last one, in a way that is true to the spirit of the Enlightenment. He always gives first place to our rational ability to:

• Reflect on our own mental capacities and achievements.
• Correct our own thinking.
• Subject the claims of reason itself to self-limitation. In this way, human reason itself retains ultimate authority over all matters of human knowledge, belief, and action. The ultimate autonomy of human thought means that it neither can, nor must, answer to any authority outside itself.

The originality of the Critique can be highlighted by focusing on how it tries to solve two of the most difficult problems of early modern philosophy at the same time:

1. To firmly establish the principle of universal causality (the idea that every event has a cause).
2. To defend the possibility of human freedom of the will.

The great idea of the Critique of Pure Reason is that the very same insights that explain how we can have knowledge of the fundamental principles underlying a scientific view of nature are also the key to understanding how our freedom—in our intentions and our actions—is possible. This freedom often seems threatened by the rule of causality in the natural world.

Kant argues that we can know the principles of the scientific worldview with certainty because these principles express the structure of our own thought. They are therefore conditions that make our experience possible, conditions that our minds impose upon the raw data of sensation. So, in a sense, certainty about the principles of science is possible only because of a kind of human autonomy:

• We are not merely passive perceivers of sensory information flowing into us from external objects.
• We are also active cognitive agents who structure what we perceive according to the necessary conditions of our own active thought.

Thus, Kant argues that we can be certain of the fundamental principles of science. The most important of these is the universal law of causation—the assumption that every event has a cause and can therefore be explained according to a law of nature. This law underlies all scientific inquiry. Kant says we can be certain of it precisely because this law is a condition of thought that our minds must impose on our perceptions in order for us to have any coherent experience at all.

In the 17th and 18th centuries, practicing scientists used the principle of causation with increasing success. But at the same time, philosophers had cast doubt on it.

• Descartes and his follower Malebranche had tried to support it with theological foundations (based on God).
• Leibniz had arguably reduced it to a mere phenomenon (an appearance).
• Hume eventually argued it was simply the result of custom or habit.

Kant, however, argues differently. He states that a genuine, necessary connection between events is required for us to experience them as an objective sequence in time. The concept of causality, which expresses this necessary connection, is imposed on experience by our own thought as an indispensable condition for experience to be possible. Therefore, the human understanding is the true lawgiver of nature. The successes of modern science are due to science conducting its inquiries according to a plan whose basis lies a priori (prior to experience) in the structure of human thought.

At the same time, this means that nature (as we know it) should be seen as essentially an object of human sensation and thinking. The validity of the causal principle is therefore restricted to the world as it appears to us under the conditions of our experience of it. In this way, the very same account that guarantees the certainty of the principle of causation also makes room for the freedom of the human will. This is precisely what the universal rule of causation was typically thought to exclude.

According to Kant, if we understand that the principle of causality and other fundamental principles of the scientific worldview are products of our own thought that we impose on experience, this leaves open a possibility. It allows for radical self-determination of human action when we consider the human will not just as it appears in the world of cause and effect, but as it might be in itself (noumenally).

In later works, such as the Critique of Practical Reason (1788) and Religion within the Boundaries of Mere Reason (1793), Kant completes this theory. He adds the argument that only our inescapable awareness of our obligation to live up to the moral law can truly prove the reality of our freedom.

• This moral law, he claims, is given spontaneously by our own reason, and we all acknowledge its authority (even if we often fail to follow it).
• Freedom is the necessary condition for the possibility of this moral demand we make upon ourselves. If we were not free, it would make no sense to say we “ought” to do something.

However, this further argument for freedom presupposes the argument of the first Critique: that we cannot establish the principles of natural science themselves without, at the same time, revealing that their scope is limited to mere appearances.

Kant’s bold attempt to solve two of the most pressing problems of modern philosophy with one stroke has seldom been accepted by later philosophers without some qualifications or criticisms.

• Some feel that Kant’s identification of the basic principles of science with the fundamental principles of human understanding ties his philosophy too closely to the Newtonian mechanistic physics that was dominant in his time. This might leave too little room for later scientific developments, such as Einstein’s theory of general relativity or quantum mechanics.
• Others have felt that reducing the laws of science to laws of human thought doesn’t adequately account for the truly objective validity of science.
• Few have been comfortable with the idea that human freedom can be defended by placing the real arena of human decision-making “behind a veil of ignorance” in a noumenal realm.
• Many have found the idea that human freedom is our ultimate value, yet can only be realized through adherence to moral law, to be strange or paradoxical.

Yet, at the same time, broad elements of Kant’s philosophy have become essential—and therefore often almost invisible—assumptions of the modern way of thinking.

• No modern thinker truly believes that the human mind is merely a passive recorder of external facts, like a “mirror of nature.”
• Many now hold that since we can’t step outside our human point of view, it might not be as easy as Kant thought to clearly separate our own subjective contributions from the objective constitution of nature. Nevertheless, almost every modern philosophy holds, in some form, the Kantian idea that human beings make an active contribution to their knowledge.
• And although few today defend human freedom using Kant’s strict distinction between phenomenal appearance and noumenal reality, even fewer believe that the assumption of causal determinism in science prevents us from seeing ourselves as agents who make decisions based on what seem to us to be the most rational principles of value.
• Thus, many have accepted, in some form, the Kantian idea that there is a fundamental difference between the standpoint of the actor (who makes choices) and the standpoint of the spectator (who observes events). This difference is often seen as crucial to solving the problem of free will.

Even those who reject Kant’s specific solutions to the problems of grounding natural science and making sense of our moral agency must still try to solve these problems. And they must find a way to avoid what they find objectionable in Kant’s solutions. In this way, all modern thinkers are, in a sense, children of Kant, whether they are happy about this intellectual inheritance or not.

III. THE EVOLUTION OF THE CRITIQUE

The Critique of Pure Reason has often been portrayed as the product of a sudden, violent revolution in Kant’s thinking that supposedly took place around 1772. The story goes that this was like a midlife crisis for the 48-year-old thinker, causing him to reject his earlier loyalty to the Leibnizian-Wolffian philosophy. This was the systematic philosophy created by Christian Wolff (1679–1754) from the brilliant but fragmented writings of Gottfried Wilhelm Leibniz (1646–1716) that were known at the time. Wolff’s system had become the dominant philosophy in German universities after the 1720s.

Kant himself contributed to this legend with some of his own remarks. Most notably, in the introduction to his Prolegomena to Any Future Metaphysics (a short work Kant published in 1783 to help people understand the Critique, which had initially received a confused or hostile reception), he said: “it was the recollection of David Hume that many years ago first interrupted my dogmatic slumber and gave an entirely different direction to my investigations in the field of speculative philosophy.”

There were certainly major changes in Kant’s thought both before and after he published his inaugural dissertation in 1770, titled De mundi sensibilis atque intelligibilis forma et principiis (On the Form and Principles of the Sensible and Intelligible World). This was his last publication before the years of intense, private work that led to the publication of the Critique in 1781. Nevertheless, Kant has misled those who believe that all his work before this point was simply a “slumber” in Wolffian dogmatism, and that he only woke up from this slumber due to some sudden memory of David Hume’s skepticism.

In fact, Kant had been questioning fundamental parts of the Leibnizian-Wolffian system at least since 1755. This was when he published his first work devoted exclusively to philosophy, his M.A. thesis titled Principiorum primorum cognitionis metaphysicae nova dilucidatio (A New Elucidation of the First Principles of Metaphysical Cognition).

Certainly, there were major developments in Kant’s philosophical views around 1769–1770, leading to his inaugural dissertation. Then, there were further developments in his specific doctrines and his understanding of philosophical method in the period starting around 1772, which finally resulted in the publication of the Critique. Many of these were revolutionary developments, both in Kant’s own thinking and in the history of Western philosophy. Even so, the Critique of Pure Reason, as well as the other “critical” works that followed it, must be seen as the product of a continuous evolution that began at least in 1755. Throughout this process, Kant never fully accepted Wolffian orthodoxy. He continually revised his positions on both substance and method until he arrived at the Critique.

Indeed, even after publishing the second edition, Kant continued to revise and refine both his views and his arguments. This is evident in published works like the Critique of Judgment and in the manuscripts he was still working on at the end of his life (later published as the Opus postumum).

Furthermore, it’s important to understand that Kant’s mature philosophy, as first expressed in the Critique of Pure Reason, does not represent an outright rejection of the philosophy of his predecessors, especially the original philosophy of Leibniz. On the contrary, Kant’s philosophy can be seen as an attempt to synthesize—to bring together and combine—several major influences:

• Leibniz’s vision of a “pre-established harmony” between the principles of nature and the principles of “grace” (morality and God’s plan).
• The core substance of Newtonian science.
• The moral and political insights of Jean-Jacques Rousseau (1712–1778).

To the extent that Kant was a critic of the Leibnizian-Wolffian philosophy, his criticisms were inspired not only by Hume but perhaps even more so by Christian August Crusius (1715–1775), who was a Pietist critic of Wolff. These critical influences led Kant to transform earlier visions. He took Leibniz’s idea of a harmonious world of simple substances (monads) under the rule of God, and Rousseau’s vision of a social contract expressing a “general will,” and reinterpreted them. For Kant, these became ideals of human reason.

• He did not claim we could prove that these ideals actually exist as facts, based on well-founded judgments within the limits of human senses and understanding.
• Instead, he argued that these ideals can and must represent the ultimate, even if never completely attainable, goals of human thought and action, both in our theoretical understanding of the world and in our practical, moral conduct.

We cannot offer a full account of Kant’s intellectual development here. But we will comment briefly on a number of the works Kant published up through 1770, in order to point out some of the ideas that were incorporated into the Critique of Pure Reason as well as some that had to be rejected or overcome before the Critique could take shape.

Next, this introduction will briefly touch on evidence of Kant’s thinking during the so-called “silent decade” from 1770 to 1781. Discussing the origins of the Critique of Pure Reason in this way can help readers understand the book’s aims. It can also shed some light on why its organization and arguments are so complex.

Early Works: Seeds of the Critique

A New Elucidation of the First Principles of Metaphysical Cognition (Nova dilucidatio, 1755)

In his first book on metaphysics, published in 1755, Kant already challenged some of the most basic ideas of the dominant Leibnizian-Wolffian philosophy, even while he still agreed with other aspects of it. Several of the most important criticisms Kant made in this early work would reappear later in the Critique of Pure Reason.

There are four main critical points from the Nova dilucidatio worth noting:

1. Kant rejected the idea of a single, absolute, first principle for all truths.

   • Christian Wolff, perhaps more so than Leibniz, was committed to this idea. Kant disagreed.
   • Kant made a logical point: affirmative truths (statements that something is) rely on the principle “whatever is, is.” Negative truths (statements that something is not) rely on the principle “whatever is not, is not.”
   • He argued that the logical rule that “the opposite of a true statement must be false” is itself a basic assumption of any logical system. It’s not something that can be proven by a logical system.
   • This was not yet his famous later distinction between analytic judgments (which are true by definition or logic alone) and synthetic judgments (which go beyond logic and add new information).
   • However, it shows that from the very beginning of his career, Kant was skeptical that all philosophical truth could be derived from one single underlying principle. This challenged Leibniz’s related theory that all true statements could, in principle, be proven simply by analyzing their concepts.

2. Kant rejected the proof for the “principle of sufficient reason” offered by Wolff and his follower Baumgarten.

   • The principle of sufficient reason states that everything must have a reason or ground that explains why it is the way it is.
   • Kant found their proof flawed. They argued that if something lacked a sufficient ground, then its ground would be “nothing,” which would mean “nothing” is “something”—a contradiction. Kant saw this as circular reasoning (assuming the very thing they were trying to prove) and merely a play on words.
   • Kant offered his own alternative argument at the time: in every true statement, the subject must be definite concerning any quality (predicate) that might be asserted of it. So, there must always be something that determines whether a given quality is true of that subject.
   • Crucially, this early attempt by Kant already shows his characteristic tendency to transform ontological questions (questions about what sorts of things must exist or the nature of being) into epistemological questions (questions about the conditions under which it’s possible for us to make claims to know things).
   • This shift in focus—from “What kinds of things are there?” to “How can we know about things?”—would develop into a full philosophical method and become key to the Critique of Pure Reason. As Kant would later say in the Critique, the “proud name of ontology,” which claimed to offer certain, a priori knowledge of things in general, “must give way to the modest one of a mere analytic of pure understanding” (an analysis of how our understanding itself works).

3. Kant rejected the “ontological argument” for God’s existence. (He later gave this famous argument its name).

   • This proof, used by St. Anselm and revived by Descartes and Leibniz, claimed that God’s existence could be inferred simply from the concept of God (e.g., if God is defined as a supremely perfect being, and existence is a perfection, then God must exist).
   • Kant’s early criticism was that this proof is “ideal” (it’s about concepts) rather than “real” (about actual existence). It only unpacks what we might have included in our concept of God; it cannot establish that there is any real object that actually matches that concept.
   • At this stage, in 1755, Kant offered his own alternative argument: that the real existence of God must be accepted as the ground of all possibility. (He would later reject this argument too in the Critique of Pure Reason).
   • However, his core criticism of the ontological argument—that it wrongly treats existence as a mere property contained in a concept—remained essentially unchanged throughout his career.
   • His critique of the ontological argument was another forerunner of the Critique of Pure Reason’s foundational distinction between analytic judgments (true by analyzing concepts) and synthetic judgments (which add new information).
   • In the Critique, Kant would argue that all important truths in mathematics, physical science, and philosophy itself, although they might be necessarily true and knowable independently of any particular experience (which he would call a priori), go beyond what can be derived from the mere analysis of concepts. Therefore, discovering and proving these truths would require a whole new method of thinking, beyond the method of conceptual analysis used by his predecessors like Leibniz, Wolff, and Baumgarten.

4. Kant rejected the basic principle of Leibniz’s monadology, a view also held by Baumgarten.

   • Monadology is the theory that everything true of a substance (a “monad,” or simple, fundamental unit of reality) is true because of the inherent nature of that substance itself. What appear to be real interactions between different substances are, in this view, only reflections of a harmonious plan God chose when creating the world. This world is the best of all possible ones precisely because it is harmonious.
   • Kant, in contrast, maintained what he called the Principle of Succession: “No change can happen to substances except insofar as they are connected with other substances; their reciprocal dependency on each other determines their reciprocal changes of state.” This means substances really do interact and influence each other.
   • He used this principle to argue for a system of “physical influx” (real interaction), a view his teacher Martin Knutzen had used against monadology.
   • The argument for a system of real interaction among all physical objects in space and time would become a crucial part of the “principles of empirical thought” that Kant would argue for in the Critique.
   • Furthermore, from this “Principle of Succession,” Kant also derived a special argument: all changes among our perceptions must be explained as due to changes in physical bodies. This served as a proof for the “real existence of bodies.”
   • When Kant later rephrased this argument, changing it from an ontological one (about what exists) to an epistemological one (about the conditions of our knowledge), it became the basis for the “Refutation of Idealism” in the second edition of the Critique of Pure Reason.

So, Kant’s first philosophical work already contained some of his most characteristic criticisms of the philosophers who came before him, as well as some of the important conclusions of his mature work. What he still needed was a new philosophical method that could take him beyond his own, still somewhat shaky, early arguments for these conclusions and provide a completely new foundation for them. Discovering that method would take him at least two more decades.

Before leaving the Nova dilucidatio, however, it’s important to mention several points where Kant still agreed with his predecessors, especially Leibniz. These were ideas that he would only subject to serious criticism later on.

1. Freedom of the Will:

   • The Nova dilucidatio includes a long dialogue on this topic. At this early stage, Kant recognized only two traditional options:
     • Determinism: Every event, including every human action, is entirely determined by a preceding sequence of events. For human actions, this chain could go back to earlier involuntary events in the person’s life, or even to events before their life began.
     • Indeterminism: A free human choice is in no way determined by any prior history. Kant associated this view with the philosopher Crusius, calling it the “indifference of equilibrium.” Kant firmly rejected this position, believing it would undermine any reasonable idea of responsibility.
   • Instead, in 1755, Kant adopted Leibniz’s position. This was a form of determinism now usually known as compatibilism. According to this view:
     • All events, including human actions, can be causally explained.
     • However, some human actions are due to an inner cause or principle (e.g., the person’s own mind representing the chosen action as the best thing to do) rather than an outer cause.
     • Actions caused in this way, even if they might be necessary and predictable, can still be called spontaneous, voluntary, or free.
   • By the time he wrote the Critique of Practical Reason (many years later), Kant would harshly reject this Leibnizian idea of freedom, famously calling it the “freedom of a turnspit” (implying it’s no more free than a machine).
   • A fundamental task of the Critique of Pure Reason—a task Kant had not yet foreseen in 1755—would be to make way for a third alternative between traditional determinism and indeterminism.
   • Kant would achieve this through his transcendental idealism. His distinction between things as they necessarily appear to human minds and how those things (including human beings themselves) might be in themselves would allow him to reconcile aspects of both the Leibnizian and Crusian positions. He could maintain that Leibnizian determinism describes the world of appearances (phenomena), while Crusian-style freedom might be true of things in themselves (noumena).

2. The Principle of Coexistence:

   • This was another Leibnizian idea that Kant initially accepted. It’s the thesis that “Finite substances do not, in virtue of their existence alone, stand in a relationship with each other, nor are they linked together by any interaction at all, except insofar as the common principle of their existence, namely the divine understanding, maintains them in a state of harmony in their reciprocal relations.” In simpler terms, things don’t interact on their own; God keeps them in harmony.
   • Even though rejecting this principle logically follows from his own “Principle of Succession” (which said substances do interact), Kant did not yet see this contradiction.
   • He would continue to hold this part of Leibnizian metaphysics through his 1770 inaugural dissertation. This was despite the fact that the 1770 work would reject fundamental aspects of Leibniz’s theory of space and time and introduce Kant’s own mature theory of them.
   • It would not be until the Critique of Pure Reason itself that Kant would fully recognize that thoroughgoing interaction among physical objects is a necessary condition for the unity of our own experience of space and time. He would also realize that the unity of the physical world has no other ground than the unity of our experience. Coming to this recognition was one of his major accomplishments during the 1770s, leading up to the Critique.

Works of the 1760s: Further Steps

Around the time of the Nova dilucidatio, Kant published two other works in natural science that would help provide a foundation for his later philosophy:

• Universal Natural History and Theory of the Heavens (1755)
• The Employment in Natural Philosophy of Metaphysics combined with Geometry, of which Sample I contains the Physical Monadology (often called his Physical Monadology) (1756)

However, the next period of major philosophical publication for Kant was from 1762 to 1764. During these years, Kant published four philosophical works, all of which are important stepping stones to the Critique of Pure Reason. Three of these works seem to have been completed in the fall of 1762, possibly in this order:

1. The False Subtlety of the Four Syllogistic Figures (published 1762)
2. The Only Possible Basis for a Demonstration of the Existence of God (published 1763)
3. Inquiry concerning the Distinctness of the Principles of Natural Theology and Morality (This essay won second prize in a competition held by the Berlin Academy of Sciences; an essay by Moses Mendelssohn won first prize. Published 1764). Finally:
4. Attempt to Introduce the Concept of Negative Magnitudes into Philosophy (completed and published by summer 1763).

The essay on False Subtlety (1762) was primarily concerned with simplifying the many classes of syllogisms (forms of logical argument) recognized in Aristotelian logic. At first glance, it might seem to contribute the least to the emergence of the Critique of Pure Reason. But in its “Concluding Reflection,” Kant touches on a theme that would be crucial for both formulating and solving virtually all the philosophical problems dealt with in the Critique. This is the claim that the fundamental notion in formal logic, and in analyzing the powers of the human mind, is the notion of judgment.

• Concepts, Kant argues (which link qualities or predicates to one another), can become distinct and clear only by means of judgments.
• Inferences (or reasoning), which might seem to require mental powers beyond judgment, are in fact just complex or repeated judgments.
• Thus, Kant concludes that “understanding and reason, that is to say, the faculty of cognizing distinctly and the faculty of syllogistic reasoning, are not different fundamental faculties. Both consist in the capacity to judge…”

The recognition that judgment is the fundamental form of all cognitive acts would be crucial to the Critique in three ways:

1. Kant would formulate the central problem of philosophy itself as the problem of how synthetic a priori judgments are possible. That is, how can judgments go beyond merely analyzing concepts (be synthetic) yet also claim universal and necessary validity (be a priori)?
2. He would argue that the necessary conditions for applying the categories (which he would derive from the logical forms of judgment) to the spatiotemporal form of human experience are the source of all those synthetic a priori judgments that theoretical philosophy (as distinct from practical or moral philosophy) can actually prove.
3. He would argue in the “Transcendental Dialectic” of the Critique that the fundamental illusion of traditional metaphysics is to think that human reason gives direct theoretical insight into how things are in themselves. Instead, Kant would claim, reason simply connects simpler judgments of the understanding into the more complex judgments we call syllogisms or inferences. Kant’s insistence in False Subtlety on the primary importance of judgment in human thought is a first step toward all these critical theses.

In a longer work from this period, the small book The Only Possible Basis for a Demonstration of the Existence of God (1763), Kant’s thought advanced toward the Critique from a different direction. The book’s argument has two main parts.

In the first section, as the title suggests, Kant discusses proofs of God’s existence.

• On one hand, he refines his original criticism of the ontological argument. He also adds criticisms of two other traditional arguments:
  • The argument from the contingency of the world (that it could have been otherwise) to the necessity of its cause. This argument had been popularized by Leibniz, and Kant would later call it the cosmological argument.
  • The argument from the order and design of the world to an intelligent author of it. This “argument from design” was widely popular among 18th-century thinkers, and Kant would later call it the physico-theological argument.
• On the other hand, Kant refines and extends his own argument from the Nova dilucidatio: that the existence of God can be demonstrated as an actual and necessary condition for anything else to be possible at all. This argument relies on the premise that it would be impossible to deny that something is possible.
• From this concept of God as the necessary ground of all possibility, Kant then tries to derive traditional attributes of God, such as uniqueness, simplicity, unchangingness, and even the claim that this necessary being is a mind.

Introducing God as the ground of all possibility must have seemed to Kant, at the time, to be logically sounder than the ontological argument. It also likely seemed more theologically orthodox than Leibniz’s view, where God’s power in creating the universe appeared to be constrained by the pre-existence of specific possible worlds. But in the Critique of Pure Reason, Kant would ultimately reject this argument of his own, as well as the three traditional ones. He would then argue that both the existence and the attributes of God could only be demonstrated on moral grounds, as practical beliefs rather than as theoretical, provable facts. Nevertheless, the underlying idea of Kant’s argument in The Only Possible Basis was remarkably deep-seated in his thought. This was the idea that a genuine or “real possibility” is not established just by showing that a concept is free from contradiction. Instead, a real possibility must have some sort of positive ground in actual existence. This idea would reappear not just in the structure of Kant’s theoretical philosophy in the Critique, but also at crucial points in his practical (moral) philosophy.

The second main section of The Only Possible Basis shows Kant’s early concern with finding a proper way to characterize scientific laws of nature. It also reveals that Kant’s complex view of teleology (the study of purposes or final causes in nature) was actually a longstanding part of his thought. It wasn’t something he added late in the process of writing the Critique of Pure Reason (where it’s only touched on in the appendix to the “Transcendental Dialectic”) or developed fully only in the much later Critique of Judgment.

In the philosophical discussions of his time about how God interacts with the world (debates between “occasionalism” and “pre-established harmony”), Kant argued that God’s purposes for the world would be shown through unchanging natural laws. These laws would be valid throughout the world’s entire history. God would not need to make miraculous, one-off interventions. Kant wrote: “Where nature operates in accordance with necessary laws, there will be no need for God to correct the course of events by direct intervention; for, in virtue of the necessity of the effects that occur in accordance with the order of nature, that which is displeasing to God cannot occur.” Thus, Kant argued that in good philosophical practice, there’s a rule (even if not formally stated, it’s always followed): “that in investigating the causes of certain effects one must pay careful attention to maintaining the unity of nature as far as possible.”

Here, in The Only Possible Basis, Kant defined an ideal for human knowledge. This ideal would be central to the Critique of Pure Reason and all his later works, even as its direct theological foundation in the idea of God became less emphasized in his philosophy. This ideal of knowledge can be described as follows:

• To have knowledge of events in an objective world (a world beyond one’s own private consciousness) is to understand those events as following causal laws.
• To have knowledge of causal laws is to see those laws as part of a larger system of laws.
• We can only conceive of such a system as if it had been created by an intelligence like our own, but much more powerful—even if we don’t claim it was actually created by God.

Although Kant did not yet see how much effort this would involve, his task in the Critique of Pure Reason and his later works would be precisely this:

• To show that knowledge of the “unity of nature”—that is, of constant laws of nature—is a necessary condition for the unity of our own experience.
• To explain how knowledge of such laws of nature is itself possible for us.

Kant’s thinking about the problem of causal laws would be developed further in the last of the four key works from the period 1762–1763, the essay on Negative Magnitudes. But before discussing that, this introduction will consider the different steps Kant took toward the Critique in the third of these works: the Inquiry concerning the Distinctness of the Principles of Natural Theology and Morality. Kant wrote this work in late 1762. He submitted it to the Academy of Sciences in Berlin by January 1, 1763, which was the deadline for the Academy’s essay competition. The competition question was whether metaphysics (which was understood to include natural theology and ethics) could achieve the same certainty as mathematics and whether it could use the same method. The Academy, still largely influenced by Wolffian philosophy, awarded first prize to Moses Mendelssohn for his elegant restatement of basic Wolffian ideas. However, the Academy recognized the merits of Kant’s essay with an honorable mention and published it along with Mendelssohn’s essay (though publication didn’t happen until 1764).

Following the rationalist tradition, Mendelssohn argued that the methods of mathematics and philosophy were similar. He even added a twist: he suggested that the certainty of metaphysics could be even greater than that of mathematics.

• Mendelssohn on Mathematics: He argued that proving mathematical theorems from their starting points (premises) depends only on applying logical principles to mathematical concepts. However, he believed that the actual truth of mathematical statements is an empirical matter—it depends on the undeniable but still observational fact that the basic concepts of our mathematics fit our experience. (This view of mathematics might still be considered plausible by some philosophers today.)
• Mendelssohn on Metaphysics: He held that metaphysical arguments mostly proceed along the same lines as mathematical proofs. The one difference, he thought, was that in two key areas, the connection of the formal system of proof to reality does not have to be made through experience (empirically) but is also secured on purely conceptual grounds.
  1. These two cases were the metaphysics of the soul (what Kant would later call “rational psychology”). Here, Descartes’ famous “I think, therefore I am” (the cogito) proves the existence of the soul in a non-empirical way.
  2. The second was the metaphysics of God (or “rational theology”). Here, Mendelssohn accepted the ontological argument as proving God’s existence from the mere concept of God.
• Since, in these central parts of philosophy, claims about existence could supposedly be proven without relying even on the most secure observation, Mendelssohn judged that philosophy had the potential for even greater certainty than mathematics.

Although Kant wrote his Inquiry without having seen Mendelssohn’s essay beforehand, he was of course familiar with the Wolffian philosophical background that Mendelssohn was drawing on. In his essay, Kant criticized the methodological assumptions of Wolffianism more strongly than he ever had before. As a result, his essay was diametrically opposed to Mendelssohn’s. This essay by Kant takes major steps toward the position he would later hold in the Critique of Pure Reason, although crucial differences still remained.

Kant’s most radical departure from the prevailing orthodoxy, and his biggest step toward the Critique in this essay, comes in his account of mathematical certainty.

• Instead of agreeing with the common view that mathematics proceeds by a two-part process (first analyzing concepts, then confirming the results by comparing them with experience), Kant argued for something new.
• He claimed that in mathematics, definitions of concepts—no matter how similar they might seem to everyday ideas—are artificially constructed by a process which he, for the first time, called “synthesis.”
• Mathematical thinking then gives itself objects “in concreto” (concretely) that fit these definitions. In other words, mathematics constructs objects for its own concepts based on the definitions it has created.
• For example, whatever the concept of a “cone” might mean in ordinary conversation, in mathematics, the concept of a cone “is the product of the arbitrary representation of a right-angled triangle which is rotated on one of its sides.”
• Thus, Kant argued, we can have certain knowledge of the mathematical definition because we ourselves construct it. And we can have certain knowledge that the definition correctly applies to its objects because the true objects of mathematics are nothing but objects constructed (however that might be done) according to the definitions that we ourselves have created.

In philosophy, however, Kant thought things were quite different at this stage.

• Philosophy does not begin from self-constructed and well-defined definitions. Instead, it starts from concepts that are already given to us, but often in a confused or unclear manner.
• Complete definitions of philosophical concepts come, if they come at all, at the end of philosophical inquiry, not at the beginning.
• In fact, Kant insisted, the goal of precisely defining concepts—which was so central to the academic philosophy of his time—is not the main goal of philosophy at all.
• Instead, Kant compared the proper method for philosophy to what he understood as the method “introduced by Newton into natural science.” This method involves obtaining certainty not about complete definitions, but about “those characteristic marks that are certainly to be found in the concept of any general property.” These marks can then lead to “judgments about the object that are true and completely certain.”
• The certainty of such philosophical judgments has to be grounded in something other than definitions. In the case of metaphysics, Kant suggested it’s grounded in “an immediate and self-evident inner consciousness.”
• Such sources of evidence then have to be carefully analyzed for their implications. So, while “geometers acquire their concepts by means of synthesis… Philosophers can acquire their concepts only by means of analysis – and that completely changes the method of thought.”
• Furthermore, while determinate objects can be constructed from the definitions introduced in mathematics, this is not the case in philosophy. In philosophy, the objects of knowledge are not our own constructs. Our philosophical concepts give us only abstract and indeterminate (general) knowledge of objects, rather than determinate and concrete objects themselves.
• Thus, Kant said, “in mathematics, the object is considered under sensible signs in concreto [concretely], whereas in philosophy the object is only ever considered in universal abstracted concepts.”
• So, at this point, Kant believed mathematical knowledge is certain because it is grounded on definitions of our own construction and fully determinate because concrete objects can be constructed from those definitions. Philosophical knowledge, he thought, is less certain because it depends on the analysis of given concepts, and less determinate because it yields only general judgments about objects.

Kant illustrated these differences between mathematical and philosophical method with three examples in the Inquiry:

1. Metaphysics: Following the philosopher Crusius, Kant argued that metaphysics depends not only on two distinct formal or logical principles (as Kant had already argued in 1755), but also on many “first material principles of human reason.” These material principles, such as “a body is compound” (meaning, made of parts), are “indemonstrable”—they cannot be proven by logic alone.
2. Theology (Arguments about God): He reiterated his argument from The Only Possible Basis: from the argument for God’s existence as the ground of all possibility, other attributes of God can be derived. This was meant to show how, from a certain (though incomplete) consciousness of some of a thing’s characteristics, other certain judgments can be derived. However, he also added that in further judgments, for example about God’s justice and goodness, only an “approximation to certainty” is possible.
3. Morality: Kant argued that although we may easily be able to identify some formal principles of obligation, such as “I ought to advance the total greatest perfection,” such principles are useless without material principles of obligation. These material principles tell us what an abstract concept like “perfection” actually means in practice—what specific courses of action actually contribute to perfection. And, Kant claimed, such material principles are themselves indemonstrable.

In the Inquiry, Kant is clearly working his way toward several of the central ideas of the Critique of Pure Reason.

• Although he does not yet speak of “analytic” or “synthetic” judgments, his distinction between analytic and synthetic methods is leading in that direction. Traditionally, this contrast between methods was merely about the direction of reasoning in an argument (e.g., from cause to effect, or from general principles to specifics). But for Kant here, the difference had become one between constructing concepts or their definitions (the synthetic method, used in mathematics) and unpacking given concepts to get to definitions (the analytical method, used in philosophy). This would eventually lead to his famous distinction between synthetic judgments (which construct fuller concepts by adding new information to what is given) and analytic judgments (which merely clarify or explicate given concepts by showing what qualities they already contain).
• Furthermore, Kant’s argument that both metaphysics and morality depend upon indemonstrable material principles, and not just formal or logical principles, is clearly preparing the way for a fundamental idea of his mature philosophy: that the basic propositions of both theoretical knowledge and morality are synthetic yet a priori judgments (they add new information but are known with certainty, independent of specific experiences).

However, Kant’s conception of philosophical method in the Inquiry had not yet caught up to this developing insight. He was at a loss to explain how we can know these “indemonstrable” material principles if the method of philosophy is still considered to be purely analytic, rather than synthetic like the method of mathematics. Before Kant’s mature work could be written, he would have to discover a philosophical method that could yield “material” or synthetic judgments with certainty. This would be the philosophical work of the 1770s that would finally pave the way for the Critique of Pure Reason.

Once Kant takes this further step (of finding a synthetic method for philosophy), the contrast between mathematics and philosophy that he drew in the Inquiry would have to be revised.

• The difference between mathematics and philosophy would no longer simply be that mathematics uses the synthetic method and philosophy uses the analytical method.
• On Kant’s mature account in the Critique, both mathematics and philosophy must use a synthetic method.
• This does not mean that the account from the Inquiry would be completely thrown out. Rather, the difference between the concrete constructions of mathematics and the abstract results of philosophy would have to be re-explained as a difference within the synthetic method itself:
  • The use of the synthetic method in mathematics would yield synthetic yet certain results about determinate objects (because mathematics constructs these objects from its definitions).
  • The use of the synthetic method in philosophy would yield synthetic yet certain principles for the experience of objects in general. These principles would include what Kant later called “schemata” of the pure concepts of the understanding—the “true and sole conditions for providing [these pure concepts] with a relation to objects” and allowing them to apply to experience.
• Thus, the Inquiry already contains key aspects of Kant’s mature theory of mathematics. What it doesn’t yet see is that both mathematics and philosophy must use synthetic methods. Once Kant realizes this, however, then the Inquiry’s distinction between the concrete results of mathematics and the abstract results of philosophy can be kept. It will then be understood as the difference between the construction of determinate mathematical objects and the construction of philosophical principles for the possibility of experiencing objects in general.

The last of the essays from the 1762–1763 period, the Attempt to Introduce the Concept of Negative Magnitudes into Philosophy, focuses on a specific substantive issue rather than on methodology.

• Kant considers various kinds of relationships that must be understood as real opposition rather than as logical contradiction. Examples include:
  • Positive and negative numbers.
  • Motion in opposite directions.
  • Pleasure and pain.
• Asserting a proposition and its direct opposite (its contradictory) results in a logical contradiction, which asserts nothing at all (e.g., “It is raining and it is not raining”).
• However, combining equal motions in opposite directions does not result in a logical nothingness; it results in a state of rest, which is a real state of affairs.
• So, Kant argued, all sorts of sciences need to make room for the concept of positive and negative magnitudes (representing real opposition), not just for the logical notion of contradiction.
• Kant’s underlying thought here, already hinted at in the Inquiry, is that the formal, logical laws of identity and contradiction are not sufficient principles for achieving knowledge of the objective world. Philosophy must find room for material principles—principles that have real content about the world.
• He concludes this essay by noting that the relation between cause and effect, although it is not a relation of opposition like positive and negative, is also a real relation rather than a merely logical one. It cannot be justified by any mere analysis of concepts that tries to show the consequence (the effect) is somehow logically “contained” in the ground (the cause).
• This raises a fundamental question for Kant: “How am I to understand the fact that, because something is, something else is?” In other words, how do we understand real connection and dependence in the world, especially causality?
• The problem of understanding real opposition, real causation, and more generally, real relations, becomes the fundamental substantive problem of theoretical philosophy for Kant.
• He rejects an attempt by Crusius to solve this problem. He makes no mention of David Hume’s formulation of an empirical (experience-based) solution to this problem, even though Hume’s Enquiry concerning Human Understanding was already available in a German translation at that time (1755).
• But Kant concludes the essay with these prophetic words: “Let us see whether we can offer a distinct explanation of how it is that, because something is, something else is canceled, and whether we can say anything more than I have already said on the matter, namely that it simply does not take place in virtue of the law of contradiction. I have reflected upon the nature of our cognition with respect to our judgment concerning grounds and consequences, and one day I shall present a detailed account of the fruits of my reflections.”

Kant published three more significant works during the 1760s:

1. Observations on the Feeling of the Beautiful and Sublime (1764).
2. Dreams of a Spirit-Seer, Elucidated by Dreams of Metaphysics (1766). This was a devastating critique of the claims of Swedenborgian spiritualism, which Kant saw as an extreme and unfounded example of metaphysics. Interestingly, it also contained some early ideas that anticipated his later moral theory.
3. A short essay, On the Ultimate Ground of the Differentiation of Directions in Space (1768). In this essay, Kant used the existence of incongruent counterparts (for example, a right hand and a left hand, or right-threaded and left-threaded screws, which are mirror images but cannot be perfectly superimposed) to argue for a Newtonian conception of absolute space. He argued against a Leibnizian conception of space, which saw space merely as a representation of a system of relations among objects that could, in principle, be captured by purely conceptual relations. Such a relational view, Kant thought, would leave out the real difference of direction between otherwise identical objects like a pair of gloves or screws.
   • Once again, Kant was concerned with the difference between logical relations and real relations. But in this brief essay, he did not yet have his own theory of how we could know something like absolute space, nor did he draw any general philosophical conclusions from this specific issue about the nature of space.

The Inaugural Dissertation (1770): A Major Shift

This situation was to change in Kant’s next major work. This was also the last of his publications on the path to the Critique before the “silent decade” of the 1770s. This work was Kant’s inaugural dissertation, titled De Mundi Sensibilis atque Intelligibilis Forma et Principiis (On the Form and Principles of the Sensible and Intelligible World).

• He defended and published it in August 1770. This was after his long-awaited appointment to the chair of logic and metaphysics at the University of Königsberg on March 31 of that year.
• The dissertation is presumed to have been written between March and August 1770.
• However, Kant had begun to mention the possibility of writing a systematic work on new foundations for metaphysics as early as 1765. His publisher had even listed a forthcoming book by him titled The Proper Method of Metaphysics in the autumn book fair catalogue of that year.
• But whatever plan he may have had at that time had not come to fruition. It was not until the formal occasion of his professorship demanded it in 1770 that Kant wrote another systematic work. As it turned out, this dissertation was an essay more on the substance (the content and basic principles) of metaphysics rather than just its method.

This work, the Inaugural Dissertation of 1770, is a milestone in Kant’s progress toward the Critique of Pure Reason. This is because it introduces the fundamental distinction between two main capacities of the mind:

1. The sensible capacity: This is our ability to have singular, immediate representations of particular objects by means of our senses. Kant from this point on calls this “intuition.”
2. The intellectual capacity: This is our ability to form abstract and general representations, or concepts, by means of our intellect (our thinking mind).

Furthermore, as the title of his dissertation suggests (“On the Form and Principles of the Sensible and Intelligible World”), Kant argues that our capacities for intuition and for forming concepts each have their own characteristic forms, principles, or laws. He believed these forms and laws can be known by us and that they form the basis of metaphysical knowledge.

Moreover, in this work, Kant introduces the doctrine that he will later call “transcendental idealism.” He argues that the “laws of intuitive cognition”—that is, the laws governing how our senses represent things—characterize how things necessarily appear to us. They do not, however, show how things actually are in themselves, independent of our minds.

By contrast, at this stage in 1770 (though he would change this view later), Kant held that intellectual representations of things, or concepts, present things “as they are.” Thus, in the Inaugural Dissertation, sensibility and intellect provide two different accounts of objects:

• Phenomena: These are things as they appear to our senses.
• Noumena: These are things as they really are, and as they are known to be by the intellect (the Greek word for intellect is noûs).

According to this 1770 account, sensibility and the intellect operate essentially independently of one another. The main reason for this radical distinction seems to have been Kant’s discovery, probably around 1769, of a way to resolve several paradoxes about the infinite. These paradoxes were well-known and much discussed by 18th-century philosophers.

• An example of such a paradox is the conflict between two ideas:
  • Time appears to have no beginning.
  • Yet, any object, and therefore any universe of objects, must have had a beginning.
• Kant thought he could resolve such conflicts by distinguishing between:
  • The forms of intuition (belonging to sensibility) as giving us only the forms of appearance.
  • The forms of thought (belonging to the intellect) as giving us the forms of reality.
• Thus, he could argue, for example, that there is no contradiction between the sensible appearance that time has no beginning and the reality (known by the intellect) that all existence must have some beginning. This is because sensibility and intellect are not presenting the same things; one presents appearance, the other reality.

In the Critique of Pure Reason, Kant would call this set of paradoxes—which he aimed to resolve through the distinction between phenomena and noumena—the antinomies of pure reason.

However, there is also a crucial difference between Kant’s way of dealing with the antinomies in 1770 and his eventual approach in 1781 (in the Critique). This difference is connected to an equally fundamental change in how Kant conceived the relationship between our two basic mental capacities: intuition (from sensibility) and conceptualization (from the intellect).

• In the 1770 Dissertation: Kant supposed that the intellect alone reveals the true nature of reality. He thought the antinomies were to be resolved by preventing any limits that are inherent in the laws of sensibility (how things appear) from being wrongly taken as limits on purely intellectual knowledge of reality.
• The problem with this 1770 view: Kant didn’t actually have an adequate explanation for how concepts play a role in our knowledge of ordinary objects in space and time.
• After 1772 (leading to the Critique): Kant would realize that concepts from the understanding must be used together with the intuitions or data supplied by sensibility. This joint use is necessary to explain how we can have knowledge of ordinary objects. Concepts and intuitions cannot work independently to produce such knowledge.
• Once he realized this, he would also have to revise his account of the antinomies. His new resolution would be that we can have no knowledge of any spatiotemporal reality (reality in space and time) at all beyond the limits of our sensibility. However, in cases where concepts of the understanding can be used to form coherent ideas about non-spatiotemporal entities (most importantly, God), there might be room for coherent belief, even if not actual knowledge.

In sum, in the Inaugural Dissertation of 1770, Kant introduces his fundamental distinction between intuitions and concepts. He uses that distinction to try to resolve the antinomies. However, he does not yet realize that knowledge can arise only from the conjoint use of intuitions and concepts to produce a unified experience. Once he comes to that realization, he will have to transform his way of resolving the antinomies. He will have to give up the view that sensibility gives us knowledge of appearances while the intellect gives us metaphysical knowledge of things as they are in themselves. Only then will the way be open for Kant’s fully mature position, presented in the Critique of Pure Reason: that knowledge has its limits, and beyond these limits, certain beliefs are possible (though they cannot be knowledge) and can be justified on practical (moral) grounds.

This introduction will now describe the contents of the Inaugural Dissertation in some detail. This will be helpful for reading the Critique, as it allows us to see exactly what Kant could keep from this earlier work and what had to be fundamentally revised.

Kant signals the importance of the problem of the antinomies from the very beginning of the Dissertation. He opens the work by stating that “just as analysis [breaking things down] does not come to an end until a part is reached which is not a whole, that is to say a SIMPLE, so likewise synthesis [building things up] does not come to an end until we reach a whole which is not a part, that is to say a WORLD.” He then argues:

• The world of appearances is given to us with space and time as its form.
• Space and time are continuous quantities (they can always be further divided).
• Therefore, in the world of appearances, there can be “no limit” in analysis (in the “regression from the whole to the parts,” or dividing things smaller and smaller).
• Similarly, there’s “no limit” in synthesis or composition (in the “progression from the parts to the given whole,” or building up larger and larger wholes).
• Thus, in the world of appearances, we can never satisfy the opening definitions of a truly simple part or a complete world.
• However, Kant then claims that the pure concepts of the intellect give us access to a realm of things with their own principles of form. In this intellectual realm:
  • Parts are not spatiotemporal regions (regions of space and time).
  • The principle of how things are put together is not based on spatiotemporal extension.
  • Instead, in this realm, the parts are substances, and the principle of their composition is their common dependence on God.
• Therefore, Kant concluded in 1770, the conditions for metaphysical knowledge of both simple substances and a single world composed of them can be satisfied by the intellect.

The remainder of the Inaugural Dissertation is then divided as follows:

• Section 2: A fuller statement of the distinctions between intuition and concept, and between phenomena and noumena.
• Section 3: A separate explanation of the fundamental forms of intuition or sensibility (i.e., space and time).
• Section 4: A separate explanation of the laws of understanding (the intellect).
• Section 5: The concluding argument that the limits of sensibility must not be mistaken for limits on metaphysical knowledge gained through the intellect.

Regarding the later Critique of Pure Reason:

• Section 3 (on space and time) is taken over into the Critique without essential changes.
• Section 4 (on the laws of understanding) will be radically revised by the mature theory of how the understanding functions, as presented in the Critique.
• Once that revision to Section 4 is made, there must also be fundamental revisions in how the antinomies (from Section 5) are treated.

In Section 2 of the Dissertation, Kant first introduces his distinction between:

• Sensibility: He characterizes this as the “receptivity of the subject in virtue of which it is possible for the subject’s own representative state to be affected in a definite way by the presence of some object.”
• Intelligence (or rationality): He calls this “the faculty of a subject in virtue of which it has the power to represent things which cannot by their own quality come before the senses.” He also refers to this faculty as “intellect” (intellectus).

Next, he argues “that things which are thought sensitively are representations of things as they appear, while things which are intellectual are representations of things as they are.” Kant’s reasons for this major claim are not entirely clear in the Dissertation. He suggests two:

1. He states that “whatever in cognition is sensitive” should be considered as “dependent upon the subject insofar as the subject is capable of this or that modification by the presence of objects.” He assumes here that different subjects might be modified by, or respond to, the same objects in different ways. Therefore, they cannot all represent the objects as those objects really are.
2. He also argues that “objects do not strike the senses in virtue of their form or aspect,” but only in virtue of their matter. Thus, “the form of… representation… is not an outline or any kind of schema of the object, but only a certain law, which is inherent in the mind and by means of which it coordinates for itself that which is sensed from the presence of the object.” In other words, the way our mind structures sensory input (its form) comes from the mind itself, not directly from the object’s own form.

Next, in Section 2, Kant argues that there are two uses of the intellect:

1. A “logical” use: In this use, the intellect subordinates concepts (no matter where they come from) to one another according to logical rules (like the “principle of contradiction”). Kant suggests that this logical use of the intellect—which involves reflective thinking that arises when the intellect compares several appearances to produce empirical concepts—is sufficient to transform mere appearance into experience.
2. A “real” use: In this use, concepts themselves—“whether of things or relations”—are given by the intellect. Kant argues that in its real use, the intellect produces concepts such as “possibility, existence, necessity, substance, cause, etc.” These concepts, he says, “never enter into any sensory representation as parts.” Instead, they can be used “dogmatically” (to make positive metaphysical assertions) to lead to a “paradigm” of “NOUMENAL PERFECTION.” In a theoretical context, this paradigm is God; in a practical (moral) context, it is moral perfection.

Thus, in the 1770 Dissertation:

• In its merely logical use, the intellect supplies no unique concepts of its own. It merely organizes data supplied by the senses into experience or empirical knowledge.
• In its real use, the intellect does supply original concepts of its own. It uses these concepts to know a non-sensible reality as it really is, or to define a non-sensible goal for our actions.

This series of claims from the 1770 Dissertation throws light on doctrines that will appear in the later Critique of Pure Reason. However, it also raises problems that the Critique will need to solve.

First, the characterization of sensibility as a passive power of the mind and the intellect as an active power will remain central to many arguments in the Critique. However, Kant will also include sensibility under the general heading of “cognitive faculties” (Erkenntnisvermögen). Since the term “faculty” (facultas, or its German equivalent Vermögen) implies activity, this means that there is an active element in sensibility as well. This fits with Kant’s claim that the form of sensibility (space and time) is in fact supplied by the mind. So, it will be important to see that even sensibility has both a passive and an active element: our senses are acted upon by external objects, but our mind actively gives form to the sensations that are produced.

Furthermore, the two arguments Kant gives in the Dissertation for his claim that sensibility represents only the mere appearance of things (his early version of “transcendental idealism”) are both problematic:

1. His first argument is that different subjects might represent outer objects in different ways. But from this, it doesn’t necessarily follow that all those subjects represent objects other than they actually are. Perhaps there is one sort of subject who represents objects correctly while others do not—and perhaps, indeed, that one sort of subject is us.
2. His second argument is that the form of the representation of objects cannot represent the objects as they are in themselves because this form represents a “law inherent in the mind.” But there are two issues here:
   • First, there is an unstated and unargued assumption that a “law inherent in the mind” cannot also represent a form inherent in objects themselves.
   • Second, since intellectual concepts are also described as laws inherent in the mind used to give form to our representations of things, it would seem to follow that they too should only give knowledge of objects as they appear to us, and not as they really are (which contradicts what the Dissertation says about the intellect knowing things “as they are”).

Finally, there are major questions about Kant’s characterization of the “intellect” in the Dissertation.

• As we saw, he supposed that we need only the “logical” use of the intellect to generate empirical concepts and experience out of mere appearance.
• He also supposed that the “real” use of the intellect, in which it generates non-empirical concepts, is sufficient to provide knowledge of non-empirical objects. Both of these assumptions will be rejected by Kant after 1772.

1. On the one hand, Kant will come to recognize that non-empirical concepts generated by the intellect—including those he mentioned, such as “possibility, existence, necessity, substance, cause, etc.”—must be applied to the data given by sensibility in order to arrive at experience or empirical knowledge. Mere abstraction and reflective comparison will not be enough for this purpose.
2. On the other hand, Kant will also conclude that those non-empirical concepts, by themselves, cannot be used to obtain theoretical knowledge about objects we do not sense (such as God). However, he will ultimately argue that they can be used to form coherent conceptions of such objects, which can then be validated on moral grounds.

These profound revisions in Kant’s thought would also require changes in his terminology.

• In the 1770 Dissertation, Kant speaks of a single faculty, “intelligence” or “intellect,” which has both a real and a logical use.
• In the Critique of Pure Reason, Kant will distinguish between Understanding and Reason as two distinct parts (or perhaps better, aspects) of the higher cognitive faculties of the mind.
  • Understanding will be the source of non-empirical categories (or “pure concepts of the understanding”). These categories must be applied to data furnished by the senses to yield empirical knowledge. Thus, the Understanding will have a “real use,” but only for empirical objects. Furthermore, since Kant continues to believe that sensibility furnishes mere appearance, the real use of the Understanding will also be confined to appearances.
  • Reason will be a “farther” faculty. It will have a legitimate logical use when it links judgments (which are constituted with concepts from the Understanding) into more complex, inferential structures (arguments). However, Reason will have a mistaken real use if it is thought that, either by means of inference alone or by using concepts of the Understanding without accompanying data from sensibility, it can obtain knowledge of non-empirical objects such as God.
  • The only legitimate “real use” of Reason, in Kant’s mature view, will be to formulate conceptions of non-empirical objects that can be validated by moral considerations; that is, Reason has a real use only as practical reason (reason applied to moral matters).
• Thus, in the Critique, Reason will be denied the power of introducing a “paradigm” of “noumenal perfection” (like God) on theoretical grounds. However, it will retain the power of introducing the practical paradigm of “moral perfection.” It will also be able to justify a certain non-cognitive use of theoretical ideas as what Kant will come to call “postulates of practical reason.”

The few paragraphs of Section 2 of the Dissertation, then, introduce fundamental assumptions that will carry over into the Critique of Pure Reason, as well as positions that will be radically revised. The three paragraphs of Section 3 of the Dissertation, by contrast, present a treatment of the forms of intuition—space and time—that will be carried over into the Critique largely unaltered, though somewhat amplified (especially in the second edition of the Critique).

• Here in the Dissertation, Kant claims that the principle of form of the world as appearance (phenomenon) is “a fixed law of the mind, in virtue of which it is necessary that all the things that can be objects of the senses… are seen as necessarily belonging to the same whole.”
• He then argues that there are in fact two such laws or principles:
  • Time: the form of all that we sense, whether inner (like our thoughts) or outer (like external objects).
  • Space: the form of our outer sense only, that is, our sensory perception of objects we take to be distinct from ourselves.
• Kant argues that space and time are both:
  1. The pure forms of all intuitions (they are the “formal principles of the sensible world”).
  2. Themselves pure intuitions. They are not concepts abstracted from experience, but singular, unique frameworks that are immediately given to us.
• They are the forms in which particular objects are presented to us by the senses. But they are also themselves unique particulars of which we can have a priori knowledge. This a priori knowledge of space and time is the basis of our a priori knowledge in both mathematics and physics.
• However, Kant states that the “embrace of space and time is limited to actual things, insofar as they are thought capable of falling under the senses.” We have no ground for asserting that space and time characterize things that we are incapable of sensing.

In Section 3 of the Dissertation, Kant makes the following specific claims about time:

1. “The idea of time does not arise from but is presupposed by the senses.” This is because any concepts we can form from our experience of things (e.g., noticing that one event follows another) already presuppose that we can represent them as either simultaneous or successive, which requires a prior notion of time.
2. “The idea of time is singular and not general.” This is because all particular times (say, this year and last year) are thought of as parts of a single, larger, all-encompassing time. They each occupy a determinate position within this one time and are not just unrelated examples (tokens) of a general type called “time.”
3. “The idea of time is an intuition,” and indeed a “pure intuition.” It is an intuition because it is both singular (as just mentioned) and immediately given to us in all our experience. It is pure because it is given to us as presupposed by all our experience, rather than being abstracted or learned from experience. All of these claims about time will be reiterated in the Critique of Pure Reason without revision, although the explanation of them will be somewhat amplified.

Next, Kant asserts a claim about time that is not explicitly made in the initial discussion of time in the Critique but is presupposed in a number of later important parts of that work: 4. “Time is a continuous magnitude.” This means that time consists of no simple, indivisible parts. Instead, between any two moments in time, no matter how small the interval between them, there is always another, smaller interval of time.

Kant then adds more reasons to support claim (5) from Section 2: “Time is not something objective and real, nor is it a substance, nor an accident, nor a relation.” It’s important to see that this claim has both a positive and a negative side.

• The positive side is the argument that we must have a pure intuition of time. This is because time is presupposed by our ability to perceive any particular objects or states as happening at the same time (simultaneous) or one after another (successive). This restates argument (1) from before. This implies that we have a pure representation of time that is independent of any particular experience through our senses.
• However, this positive point doesn’t mean that time is also “objective and real” in a way that goes beyond being simply a form of our representation. For this further, negative claim (that time is not independently real), Kant suggests two kinds of reasons:
  1. A metaphysical reason: This was aimed against Newton and “the English philosophers.” Kant found the idea of absolute time existing as an independent substance, or as a property of any substance (like being God’s “sensory organ” or sensorium dei), to be absurd.
  2. An epistemological reason (an argument about knowledge): This was aimed against Leibniz. If we thought of time as something we merely abstract or derive from the perceived relations between objects, then our knowledge of time would be purely empirical (based on experience). According to Kant, this would “completely destroy” all the certainty of the fundamental rules of mathematics and physics (which, he believed, depend on a certain, non-empirical understanding of time). The full premises of this epistemological argument, however, are not spelled out completely before the Critique of Pure Reason, and even in the Critique, they are only hinted at.

Finally, Kant adds two more points about time: 6. Although time, if we imagine it existing “in itself and absolutely” (completely independent of our minds), would be an “imaginary being”… 7. Nevertheless, as “the universal form of phenomena” (the way all appearances, whether inner thoughts or outer objects, are structured for us), time is “to the highest degree true.” It is also “an absolutely first formal principle of the sensible world” (meaning it’s a real and fundamental structuring principle for our experience).

Kant makes a series of parallel claims about space:

1. “The concept of space is not abstracted from outer sensations.” He argues this because, “I can only conceive of something as placed outside me by representing it as in a place which is different from the place in which I am myself.” In other words, I cannot get the concept of space from my experience of objects distinct from myself because I cannot even experience them as distinct without already representing them as being in space.
2. Like the concept of time, “the concept of space is a singular representation.” This is because all particular regions of space are thought of as parts of a single, boundless, all-encompassing space, rather than as just individual examples of some general type or category called “space.”
3. From these two arguments, Kant infers that “The concept of space is thus a pure intuition.” It is an intuition because it is singular (one whole space). It is pure because it is not “compounded from sensations” but is presupposed by all “outer sensation” (our experience of objects as distinct from ourselves).
   • (Here, Kant skips a direct argument that space is a continuous quantity, though he will assume this in the Critique of Pure Reason.)
   • Instead, he inserts the argument from his 1768 essay about incongruent counterparts (like a left and a right hand, which are mirror images but not identical if one tries to superimpose them). He now uses this to argue that since features of directionality (like right-handedness and left-handedness) cannot be inferred from the mere concepts of objects, they must be “apprehended by a certain pure intuition” (namely, the pure intuition of space). (This specific argument about incongruent counterparts will be omitted from the Critique itself.)
4. Now, as he did with time, Kant infers from these results that “Space is not something objective and real, nor is it a substance, nor an accident, nor a relation; it is rather, subjective and ideal; it issues from the nature of the mind.” He supports this conclusion with several points:
   • His prior arguments that space is “the scheme… for coordinating everything that it [the mind] senses externally.”
   • A metaphysical claim made against “the English” (Newtonians): The idea of space as “an absolute and boundless receptacle of possible things” is absurd.
   • An epistemological argument made against Leibniz: If the propositions of geometry (which are taken to describe space) were merely abstracted from an experience of relations among objects, this would “cast geometry down from the summit of certainty, and thrust it back into the rank of those sciences of which the principles are empirical” (i.e., based on experience and therefore not absolutely certain).
5. Finally, Kant again concludes about space: Even though “the concept of space as some objective and real being or property be imaginary, nonetheless, relatively to all sensible things whatever… it is not only a concept that is in the highest degree true, it is also the foundation of all truth in outer sensibility.” This statement is as good a summary of the doctrine of transcendental idealism as can be found in the Critique itself. It insists on both the subjectivity (it comes from the mind) and also the universality and necessity of space as a form of our representation.

This account of space and time as the forms and principles of the sensible world, as mentioned, remains essentially unchanged in the Critique of Pure Reason. In Section 4 of the 1770 Dissertation, however, Kant gives an account of the “principle of the form of the intelligible world.” This account is still largely unchanged from his earliest philosophical work, but it will disappear from the Critique.

• The content of this section is basically just the Leibnizian argument: a multitude of substances can form a single world only because they all depend on a single, common cause (namely, God).
• This argument is based on the thoroughly Leibnizian idea that “the existence of each [necessary] substance is fully established without appealing to any dependence on anything else whatsoever.” From this, it’s inferred that contingent substances (things that depend on something else for their existence, and are the only kind that could therefore make up an interrelated whole) are characterized precisely by their dependence on a cause. Therefore, they form a single world because they all depend on a common cause.
• Kant’s attempt in the Dissertation to reconcile this argument with his longstanding attraction to the theory of “physical influx” (the idea of real, direct interaction between distinct objects) is not successful.
• However, not only will this particular Leibnizian argument disappear from the Critique, but also the underlying assumption that pure concepts of the intellect (such as the concept of substance) can be used on their own, without input from the senses, to provide knowledge of things as they are in themselves. This entire metaphysical approach will be rejected.
• This particular argument about God as the unifier of the world will be replaced in the Critique by arguments like the “Third Analogy of Experience.” The Third Analogy argues that interaction among physical objects is a necessary condition for us to experience them as simultaneously occupying different yet definite positions in a single space.
• The underlying metaphysics of the Dissertation (where the intellect knows things in themselves) will be replaced by Kant’s mature critical position: that pure categories of the understanding, when used on their own for theoretical knowledge, lead to “ideas of reason” that are illusory. These ideas, however, can serve as “postulates of practical reason” (assumptions necessary for morality).

The same kind of transformation awaits Kant’s treatment of the “method in metaphysics” in the concluding Section 5 of the Inaugural Dissertation.

• Kant begins by arguing that philosophy has no special method to prescribe to ordinary science. This is because in ordinary science, the use of the intellect is only “logical”—it organizes concepts that are not themselves provided by the intellect but are instead abstracted from experience.
• In the case of metaphysics, however—where the intellect does have a “real use” by supplying original concepts—Kant states that “method precedes all science.”
• The method of metaphysics, Kant then maintains in 1770, “amounts to this prescription: great care must be taken lest the principles that are native to sensitive cognition [knowledge from the senses] transgress their limits, and affect what belongs to the understanding [the intellect].”
• The fundamental obstacle to progress in metaphysics, according to this view, comes from assuming that the necessary conditions and inherent limits of our sensibility are also limits on the possibility of intellectual knowledge of reality.
• Kant lists three “subreptic axioms” (sneaky or hidden, unwarranted assumptions) that arise from this confusion:
  1. It is a mistake to assume that the same sensory condition, under which alone the intuition (sensory representation) of an object is possible, is also a condition for the possibility of the object itself.
  2. It is a mistake to assume that the same sensory condition, under which alone it is possible to compare what is given by the senses so as to form a concept of the understanding about the object, is also a condition for the possibility of the object itself.
  3. It is a mistake to assume that the same sensory condition, under which alone some object we encounter can be subsumed under (brought under) a given concept of the understanding, is also a condition for the possibility of the object itself.

In other words, at this stage in 1770, Kant holds that it is a mistake to assume that the characteristic forms and limits of our sensible representations—and the conditions for applying concepts to these sensible representations—also limit our metaphysical knowledge of objects as they really are (via the intellect). Kant gives examples of the errors that arise from this mistaken assumption:

• It is an error to assume that whatever exists must be located in space and time.
• It is an error to assume that “every actual multiplicity can be given numerically” (like things counted in space and time are), and therefore to conclude that “every magnitude is finite.”
• It is a mistake to assume that what might be an empirical (sensory) criterion for applying a concept (for example, non-existence at some particular time might be a sensible criterion for the modal concept of “contingency”) is actually a necessary feature for any use of that concept at all. The implication of Kant’s argument in 1770 is that paradoxes (like the world appearing to be both finite and infinite if it’s represented as existing in space and time) can arise if we try to derive metaphysical knowledge from the conditions of sensibility. His argument further implies that such paradoxes can be avoided because, he then believed, we can have intellectual knowledge of reality independently of the concepts of space and time, which he saw as mere conditions of “sensitive cognition.”

Finally, Kant concludes Section 5 of the Dissertation by mentioning, almost as an afterthought, that there are certain “principles of convenience” (principia convenientiae). These are not principles of sensitive cognition but rather rules by means of which “it seems to the intellect itself easy and practical to deploy its own perspicacity [clear-sightedness].” These principles include:

1. “All things in the universe take place in accordance with the order of nature” (the principle of universal causation).
2. “Principles are not to be multiplied beyond what is absolutely necessary” (often called “Ockham’s razor”).
3. “Nothing material at all comes into being or passes away” (the principle of the conservation of material substance). This is a striking list because it includes two principles—universal causation and the conservation of substance—that Kant will later identify as “constitutive principles.” In the Critique, these will be seen as necessary conditions for the very possibility of us experiencing objects at all. But the list also includes another principle—Ockham’s razor—that is more like what Kant will later identify as a “regulative principle.” A regulative principle is not a necessary condition for any experience at all, but rather an assumption we make for various subjective or practical reasons (e.g., to guide inquiry).

The fact that Kant, in 1770, could indiscriminately mix what he would later distinguish as constitutive and regulative principles shows that he did not yet have a clear conception of the function of constitutive principles as necessary conditions for the possibility of experience. This, in turn, was a consequence of the fact that he did not yet have a clear understanding that the pure concepts of the understanding (such as the concepts of causation and substance mentioned in these “principles of convenience”) can yield knowledge only when applied to data furnished by the faculty of sensibility. Likewise, his argument at this stage—that metaphysical illusion can be avoided by not letting the conditions of sensibility limit the use of concepts of the intellect—shows that he did not yet see that the concepts of the understanding have a cognitive (knowledge-giving) use only in application to sensibility and therefore within its limits. Beyond those limits, he would later argue, these concepts can only have a practical (moral) use. Before Kant could progress from the Inaugural Dissertation to the Critique of Pure Reason, he would have to develop a new conception of how the intellect is used. This new conception would involve clear distinctions among:

1. The sensible use of the understanding (applying concepts to experience).
2. The illusory use of pure theoretical reason (when reason tries to gain knowledge beyond experience).
3. The reliable use of pure practical reason (reason as applied to morality).

IV. THE GENESIS OF THE CRITIQUE

The “Silent Decade” and Early Developments (1770–1772)

After the publication of the Inaugural Dissertation in 1770, Kant fell into a prolonged period of relative public silence, broken only by a few minor essays and a series of important letters to his student Marcus Herz. Herz had participated in the public defense of Kant’s dissertation and was now in Berlin. There, he was studying medicine but was also in contact with the prominent philosophers of the capital city. Aside from what little can be gleaned from these letters, our primary source of information about Kant’s thought during these years (often called the “silent decade”) comes from surviving marginal notes he made in his books and other written fragments. Presumably, these are only a small part of what Kant actually wrote during this period, and they have to be used with caution. Fragmentary as they are, however, these materials cast considerable light on the emergence of some of the most important new arguments of the Critique of Pure Reason. They also help explain some of its most troublesome obscurities.

In the fall of 1770, Marcus Herz went to Berlin with copies of Kant’s dissertation for leading intellectuals such as Moses Mendelssohn, Johann Heinrich Lambert, and Johann Georg Sulzer. He also carried accompanying letters from Kant, though only the letter to Lambert survives. In this letter, Kant apologizes for not following through on an earlier promise of collaboration. He makes a new promise for the rapid publication of a work on the metaphysics of morals (a promise that would not even begin to be fulfilled for another fifteen years). Otherwise, the letter shows his continuing commitment to the view of metaphysics he had expressed in the dissertation. By Christmas 1770, all three Berlin philosophers had replied to Kant with letters. These letters contained essentially the same objection: How could Kant hold time to be a mere appearance with no objective reality? After all, time is the form of inner sense, and we all have immediate experience of changes in our inner sense (our thoughts and feelings), regardless of whatever external significance we might attribute to those changing internal states.

Lambert initially raised a question about whether Kant’s “two ways of knowing”—from the senses and from the intellect—“are so completely separated that they never come together.” But then he focused his detailed discussion only on Kant’s treatment of time. Lambert accepted Kant’s arguments that time is singular, continuous, and the object of a pure intuition. However, he objected to Kant’s idealism about time (the view that time is only a form of our minds and not objectively real). Lambert argued: “All changes are bound to time and are inconceivable without time. If changes are real, then time is real, whatever it may be. If time is unreal, then no change can be real. I think, though, that even an idealist must grant at least that changes really exist and occur in his representations, for example, their beginning and ending. Thus time cannot be regarded as something unreal.”

Sulzer’s briefer letter also raised a problem about time. He asserted that duration must have “a true reality,” even if our formal concept of time is some sort of abstraction from our experience of real duration. Mendelssohn, too, objected: “For several reasons I cannot convince myself that time is something merely subjective. Succession is after all at least a necessary condition of the representations that finite minds have…. Since we have to grant the reality of succession in a representing creature and in its alternations, why not also in the sensible objects, which are the models and prototypes of representations in the world?”

Kant made no immediate reply to this objection, as we know from a letter he wrote to Marcus Herz on June 7, 1771. He merely asked Herz to apologize to his correspondents, explaining that their letters had set him off on a long series of investigations. He then told Herz that he was now occupied with a work that, “under the title The Bounds of Sensibility and Reason, would work out in some detail the relationship of the concepts and laws determined for the sensible world together with the outline of what the nature of the theory of taste, metaphysics, and morality should contain.” In his next message, Kant said that he expected to complete the plan for this work shortly.

Kant does not appear to have written to Herz again until February 21, 1772, when he wrote what has become his most famous letter. In this letter, Kant reviewed his plan for the work he had mentioned the previous June. He stated that it was to consist of “two parts, a theoretical and a practical.”

• The first, theoretical part, would in turn consist of:
  1. A general phenomenology (a study of experience and appearance).
  2. Metaphysics, but this only concerning its nature and method.
• The second, practical part, was to deal with:
  1. The universal principles of feeling, taste, and sensuous desire.
  2. The basic principles of morality.

However, Kant continued in the letter, as he thought about the theoretical part—where the “phenomenology” was supposed to have dealt with the limits of sensitive cognition before the purely intellectual foundations of metaphysics were explained—he said, “I noticed that I still lacked something essential, something that in my long metaphysical studies I, as well as others, had failed to pay attention to and that, in fact, constitutes the key to the whole secret of hitherto still obscure metaphysics.” But the fundamental problem that Kant now announced had nothing to do with the objection to his idealism regarding time that the Berlin scholars had raised. Indeed, although Kant would eventually acknowledge their objection, he would in no way rethink his position about the ideality of time.

Instead, Kant raised a completely different question: “What is the ground of the relation of that in us which we call representation to the object?” In simpler terms, he was asking: How do our mental representations (our ideas, concepts, perceptions) actually connect to, or correspond to, objects in the world? This is a puzzle, Kant realized, precisely in the case of the relationship between pure concepts of the understanding (concepts that originate from our own minds, not directly from experience) and objects that are presented to us by sensible experience. It is not such a puzzle, he thought, in two other cases:

1. In the case of entirely empirical representations (like a direct perception of a specific tree). These are simply caused by their external objects; the object produces the representation in us.
2. In the case of divine archetypes (God’s original, perfect ideas of things) or, we might add, human intentions (our plans to make or do something). In these cases, the representation (the idea or intention) causes the object to come into being. The really difficult question—the “key” to metaphysics—was how our mind’s own concepts, which neither simply copy an object nor create it, can nonetheless relate to objects given through our senses.

But, Kant now holds (in 1772), that the pure concepts of the understanding must apply to the objects we experience through our senses. This is true even though these concepts come from our own minds (“the nature of the soul”) and are known “completely a priori” (before any specific experience). These concepts are neither caused by the objects of experience, nor do they cause those objects.

Kant now admits that he had completely overlooked this crucial question in his 1770 Inaugural Dissertation. In that earlier work, he failed to realize that our pure concepts (from the intellect) as well as our forms of intuition (space and time, from sensibility) must both apply to the same objects—namely, the objects of our actual experience. Thus, what Kant now realized he must explain is “the possibility of such concepts, with which… experience must be in exact agreement and which nevertheless are independent of experience.” With this new focus, the idea from the Inaugural Dissertation—that pure concepts of the understanding provide knowledge of entities other than the spatiotemporal objects of our senses—suddenly disappeared. The central question became how these mind-born concepts could apply to the world we experience.

In his 1772 letter to Herz, Kant did not describe how this agreement between experience and pure concepts of the understanding was to be explained. He only suggested that a systematic classification of these “concepts belonging to complete pure reason,” which he also called “categories,” could be reached by “following a few fundamental laws of the understanding.” In spite of this obscurity, Kant was confident. He told Herz he would be ready to publish the work, which he now for the first time entitled a Critique of Pure Reason, in only three months! In fact, it would be almost nine years before the book with that title appeared (in 1781). Much of this delay was because Kant did not yet have a clear idea of why the categories necessarily apply to all objects of our experience.

As Kant thought further about this problem, an issue related to time began to play a key role. This was not the earlier problem about the reality of time (whether it’s objective or just in our minds), which the Berlin philosophers had raised. Instead, it was a different problem: How can we make definite and reliable judgments about the order of objective events or even our own experiences in time? This question about establishing a determinate temporal order became a focus of Kant’s attention in the years following the 1772 letter to Herz, especially around 1774–1775. It would remain a central issue in the Critique of Pure Reason.

Kant’s next report on his progress is in another letter to Herz, written toward the end of 1773.

• Kant wrote that he would not “be seduced by any author’s itch into seeking fame.”
• He suggested that he was still working on “a principle that will completely solve what has hitherto been a riddle and that will bring the misleading qualities of the self-alienating understanding under certain and easily applied rules.”
• Nevertheless, he promised that he would have his book, which he continued to call “a critique of pure reason,” ready by the following Easter (spring 1774) or shortly after.

In Kant’s next surviving letter to Herz, however, written three years later in November 1776, we again find him suggesting that he had been held up by difficulties surrounding the fundamental principle of his new position. Though he said he had made progress with it the previous September, he once again promised the completed book by the following Easter. Yet the following August (1777) still found Kant reporting “a stone in the way of the Critique of Pure Reason.” Once again, though, he was optimistic that he could get by this obstacle during the following winter (1778). But April 1778 found Kant writing that the rumor that some pages of his book were already at the press was premature. And in August of that year, Kant would only say he was “still working indefatigably” on his “handbook” (his term for the Critique).

So, for at least five years, the completion of the promised book continued to be postponed. There were repeated hints that Kant had still not found the fundamental principle he needed—presumably the principle that would answer the fundamental question he posed in his 1772 letter. From the letters to Herz (the only one of his known correspondents in this period to whom Kant said anything at all about his planned book), it might seem as if Kant was making no progress at all. But other sources, such as Kant’s personal notes, reveal that he was indeed working “indefatigably” on the Critique throughout this period. Beginning around April 1774 – that is, around the time of his first promised Easter completion date – Kant did begin to explore a solution to his puzzle. This puzzle was about why a priori concepts of the understanding (concepts originating in the mind before experience) should necessarily apply to the data presented to us by sensibility (our senses), and why they should not have any constitutive, theoretical (knowledge-giving) use outside of that application to experience.

Progress in the Mid-1770s: Connecting Concepts to Experience

Notes from 1774–1775 (some written on the back of a letter sent to him on April 28, 1774, which he used as scrap paper) show Kant was clearly working on the Critique. Much of this material goes over claims about space and time that he had already established in the 1770 Inaugural Dissertation. But Kant now added a line of thought that had not previously appeared.

• He said that the unity of time implies the unity of the self (the thinking subject). It also implies that all objects must have a determinate (definite) position in time.
• In his words (from these notes):
  • “1. Time is unique [einig]. Which means this: I can intuit all objects only in myself and in representations found in my own subject, and all possible objects of my intuition stand in relation to each other in accordance with the special form of this intuition…” (This suggests that time is the single, unifying form of my inner sense, where all my representations are ordered).
  • “4. All things and all states of things have their determinate position in time. For through the unity of inner sense they must have their determinate relation to all other putative [supposed] objects of intuition.” (Everything must have a specific place in the timeline of my unified experience).

He then made parallel claims about space. Space is not only our unique form for representing objects external to ourselves, but it is also unified. This means every object must be assigned a definite position in relation to all others in it.

• He wrote: “Space is nothing but the intuition of mere form even without given matter, thus pure intuition. It is a single [einzelne] representation on account of the unity of the subject (and the capability), in which all representations of outer objects can be placed next to one another.” (This suggests that space is a single, pure framework provided by the unified self, where all outer objects are ordered).

Finally, Kant suggested in these notes that the use of concepts of the understanding, or rules associated with them, is the necessary condition for assigning representations (or their objects) their definite positions in a unified space and/or time.

• He wrote: “We have no intuitions except through the senses; thus no other concepts can inhabit the understanding except those which pertain to the disposition and order among these intuitions. These concepts must contain what is universal, and rules…”
• (The rest of this particular note distinguishes between a “learned understanding” for abstract rules and a “common understanding” for rules abstracted from specific cases, noting that a priori rules do not come from common understanding or experience).

This remark from 1774 is very important because:

1. It presupposes that concepts are used only when applied to intuitions (sensory data). This was a crucial thesis that Kant had not yet clearly seen in 1770 but was to become a hallmark of the Critique of Pure Reason, famously expressed in the line: “Thoughts without content are empty, intuitions without concepts are blind.”
2. It further suggests that the particular function of the a priori concepts of the understanding is to serve as rules for establishing “disposition and order” among our intuitions of objects. (Though Kant did not yet explain in detail why concepts should be necessary for this purpose or exactly how concepts function as rules for this.)
3. Finally, Kant suggested that even the ordinary use of abstraction to produce empirical concepts (concepts derived from experience) depends upon the use of these a priori concepts of the understanding to establish this fundamental “disposition and order.” This is an important point because it implies that the theory of a priori concepts to be worked out in the Critique of Pure Reason is not, as it has sometimes been seen, just a theory about the foundations of natural science considered as separate from everyday life. Rather, it is a theory of the foundations of science as continuous with all of our knowledge, including our everyday understanding of the world.

The following series of notes shows that Kant spent much of his time in the next several years trying to work out his hunch: that the categories (his term for the pure concepts of the understanding) can be shown to be a priori yet necessary conditions of all our knowledge of objects. He aimed to do this by showing that their use is the necessary condition for all definite “disposition and order” of intuitions. These notes are generally assigned to the year 1775 because one of them is written on another letter sent to Kant dated May 20, 1775. Although, as we saw, Kant had been moving toward the idea of a fundamental contrast between logical relations and real relations throughout the 1760s, it is only in these notes from around 1775 that he first clearly links his fundamental philosophical problem with the distinction between judgments that are analytic and those that are synthetic yet a priori.

• Kant asked under what conditions a predicate ‘b’ can be attributed to an object ‘x’ that is also understood through another predicate ‘a’.
• In some cases, ‘b’ can be attributed to any ‘x’ that is ‘a’ because the predicate ‘b’ is already identical to, or contained within, predicate ‘a’. We don’t need to consider or experience any particular ‘x’ to see that this is true. In such cases, a statement of the form “All x’s that are a are also b” would be true because of “the principle of identity and contradiction.” It would be a “merely logical” truth, a “principle of form rather than content”—that is, it would be an analytic judgment.
• If, however, the predicates ‘a’ and ‘b’ can be related to each other only through the object x itself, then the judgment is synthetic. In this case, the predicates are “not in a logical but in a real relation.”
• Kant also said: “In synthetic propositions the relation between the concepts is not really immediate (for this happens only in the case of analytic propositions), rather it is represented in the conditions of their concrete representation in the subject.”
• Kant did not say so explicitly in these notes, but he was clearly already assuming that propositions asserting that a priori concepts (like cause and effect, or substance) apply to the objects of our senses would fall into this class of synthetic judgments expressing real relations.

Kant’s next step was to argue that there are three different ways in which synthetic judgments may be made. The object ‘x’ (by means of which we link predicates ‘a’ and ‘b’) may be:

1. Constructed in pure intuition (as in mathematics).
2. Simply given in empirical intuition or appearance (as in everyday sense experience).
3. Or it may be (and this is the crucial third case for philosophy) “the sensible condition of the subject within which a perception is to be assigned its position.”

In another passage, he wrote: “‘x’ is therefore the determinable (object) that I think through the concept ‘a’, and ‘b’ is its determination or the way in which it is determined. In mathematics, ‘x’ is the construction of ‘a’; in experience, it is the concretum [the concrete thing given in experience]; and with regard to an inherent representation or thought in general, ‘x’ is the function of thinking in general in the subject.”

It is clear enough what Kant means by the first two options for grounding synthetic judgments:

1. In mathematics, synthetic judgments—such as “The sum of the interior angles of a plane triangle equals two right angles”—are made or confirmed by constructing an object satisfying the first predicate (“plane triangle”) in pure intuition (our mind’s a priori forms of space and time). We then see that this mental construction satisfies the second predicate as well (“equals two right angles”). Such a construction yields a determinate (definite) answer (e.g., two right angles contain 180 degrees, not 179 or 181). This is because it is the construction of a particular object. Yet, it yields a result that is a priori (universally and necessarily true) because it takes place in pure intuition, the very form that determines the structure of all possible triangles or other spatial figures or objects.
2. In ordinary experience, observation establishes synthetic and determinate propositions, but these are only contingent (they could be otherwise) or a posteriori (derived from particular experiences). For example, a statement like “My copy of the Critique is worn and dog-eared” adds information (“worn and dog-eared”) that goes beyond the initial description of the object (“my copy of the Critique”). But that additional information can only be asserted of the particular object that is observed, because it has nothing to do with any essential form of appearance.

But what did Kant mean by his third case for synthetic judgments, referred to only by such obscure phrases as “the sensible condition of a subject” or “the function of thinking in general”? This was the key to understanding how a priori synthetic judgments are possible in philosophy itself.

What Kant had in mind was what he hinted at in his notes from 1774:

• There are certain rules necessary for the “disposition and order” of our representations (our perceptions, thoughts, etc.).
• These representations must be conceived of as belonging to a unified self.
• They must also occupy determinate (definite) positions in the space and time in which that self places its representations.
• These rules (which he would later connect to the categories) add general conditions to the concept of any possible object of experience. These conditions go beyond the particular features of such objects that we might happen to observe and by means of which we might happen to refer to them.

He brought together the steps of this argument so far in this passage from his notes: “In analytic judgments the predicate [b] pertains properly to the concept a; in synthetic judgments to the object of the concept, since the predicate [b] is not contained in the concept. However, the object that corresponds to a concept has certain conditions for the application of this concept, i.e., its position in concreto [in a concrete instance]… Now the condition of all concepts is sensible; thus, if the concept is also sensible, but universal, it must be considered in concreto, e.g., a triangle in its construction. If the concept does not signify pure intuition, but empirical, then x contains the condition of the relative position (a) in space and time, i.e., the condition for universally determining something in them.”

This is still somewhat obscure, but what Kant is saying is that judgments that are synthetic but also genuinely universal (that is, a priori) can be grounded in one of two ways:

1. In the case of mathematics, such judgments are grounded in the construction of a mathematical object in pure intuition.
2. In the other case (which would apply to the foundational principles of knowledge, or metaphysics), such judgments are grounded in the condition of determining the relative position of one object in space and time to others—that is, in the general rules for ordering any object within our experience.

Kant also put this point by saying that what he was looking for are the “principles of the exposition of appearances.”

• “Exposition of appearances” means precisely the assignment of each representation (each appearance) to a definite position in the unified space and time that is the framework for all the representations belonging to a unified self.
• Kant introduced this concept when he wrote: “The principium [principle] of the exposition of appearances is the general ground of the exposition of that which is given [by the senses]. The exposition of that which is thought depends merely on consciousness, but the exposition of that which is given, if one regards the matter as undetermined, depends on the ground of all relation and on the linkage [Verkettung, or chaining together] of representations (sensations)…. The exposition of appearances is therefore the determination of the ground on which the nexus [connection] of sensations depends.”
• In essence, these principles are about how our minds structure and connect sensory data to form a coherent and ordered experience of appearances.

Perhaps a clearer statement of Kant’s developing strategy from his notes is this: “There is in the soul a principium [principle] of disposition [arranging] as well as of affection [being affected by senses]. The appearances can have no other order and do not otherwise belong to the unity of the power of representation except insofar as they are amenable to the common principio of disposition. For all appearance with its thoroughgoing determination must still have unity in the mind, consequently be subjected to those conditions through which the unity of representations is possible. Only that which is requisite for the unity of representations belongs to the objective conditions. The unity of apprehension [our grasping of appearances] is necessarily connected with the unity of the intuition of space and time, for without this the latter [space and time] would give no real representation. The principles of exposition must be determined on the one side through the laws of apprehension, on the other side through the unity of the power of understanding. They are the standard for observation and are not derived from perceptions, but are the ground of those [perceptions] in their entirety.”

Kant’s argument, as it was developing, was this:

• Although all particular representations are given to the mind in temporal form (and all representations of outer objects are also given in spatial form), these representations cannot be linked to each other in the kind of unified order the mind demands—an order in which each object in space and time has a definite relation to any other—except by means of certain principles.
• These principles are inherent in the mind, and the mind brings them to bear on the appearances it experiences.
• These principles will be, or will be derived from, the pure concepts of the understanding (the categories).
• These categories have a subjective origin (they come from the mind itself), yet they necessarily apply to all the objects of our experience.
• And, crucially, these concepts will not have any definite use except in this “exposition of appearances”—that is, in the structuring and ordering of experience. This is the theory that would eventually answer the puzzle Kant raised in his letter to Herz of February 1772 (how pure concepts relate to objects) and that would finally allow him to write the Critique of Pure Reason.

But how exactly would the categories be shown to be the necessary conditions for this “exposition of appearances”? This crucial step had by no means been made clear in anything cited from Kant’s notes so far. Kant threw out a number of tantalizing but incomplete suggestions during this period. Perhaps it was his difficulty in choosing between these suggestions, as well as in working out their details, that prevented the Critique of Pure Reason from taking its final shape before 1779.

One idea Kant suggested is that to link appearances in the orderly way needed for a unified mind or self-consciousness, certain principles must be imposed on those appearances. This is because there’s a specific way we necessarily have to think about a unified mind—what Kant then started to call “apperception” (or self-perception).

• He stated, “Whatever is to be thought as an object of perception stands under a rule of apperception, or self-perception.”
• He then claimed there’s a “threefold dimension of synthesis” because there are “three functions of apperception,” or three ways we think about ourselves. We necessarily see our own thoughts as:
  1. Having a “relation to a subject” (they are my thoughts).
  2. Having a “relation of succession among each other” (they occur one after another).
  3. “[Comprising] a whole” (they form a unified stream of experience).
• Kant suggested we therefore impose these same categories—which he would later identify as the categories of relation (substance, causality, and community/interaction)—onto the objects we represent.
• Following this line of argument, Kant said, “I am the original of all objects.” This means he thought we understand objects by comparing them to the way we must understand ourselves.

Alternatively, Kant sometimes suggested the reverse:

• We necessarily think about objects using categories like a “subject” (or substance) that has a “succession” of states and forms a “whole” of properties.
• Then, we understand ourselves and the unity of our own thoughts by comparing them to how we necessarily think about objects.
• For example, in another note, he argued: “All existence belongs to a substance; everything that happens is a member of a series; everything that is simultaneous belongs to a whole whose parts reciprocally determine each other.” He then suggested that the way we think of ourselves—as a subjective order of experiences—corresponds to these fundamental ways of thinking about objects.

In some of his most promising remarks from this period, however, Kant suggested that there might be direct arguments showing why certain categories of the understanding are necessary for specific time-determinations. These arguments wouldn’t need to rely on analogies between how we think of the self and how we think of objects.

• Thus, Kant argued that to assign definite positions to events in time, we need a framework of principles. These principles use the same categories (substance, causality, interaction) that in other passages he had linked to the concept of a subject or an object.
• His notes from this time suggest ideas like these (though expressed very densely):
  • For an occurrence to happen, something must come before it. Among the many things that could come before, there is one from which the occurrence always follows (this points towards causality).
  • For any point in time to be determined (and for something real to be attached to it), there must be something that accompanies it and helps determine that point in time. Among the many things that can accompany it, something must always be there (this points towards an enduring substance).
  • For things to be considered simultaneous (happening at the same time), there must be a connection between them, a mutual determination of these various things by one another (this points towards reciprocal interaction, or community).
  • If there were not something that always existed—something permanent and stable (a substance)—there would be no firm reference point for determining moments in time. Thus, there would be no definite perception, meaning no way to determine something as being at a specific point in time.
  • If there were not something that always preceded an occurrence (a cause), then among the many things that come before it, the occurrence would not have a definite place in a series of events.
  • Through such “rules of perception” (which involve these categories), the objects of our senses become determinable in time. In raw intuition (our direct sensing), objects are merely given as appearances. These rules allow us to find an objective order in these appearances, an order that is different from the mere subjective sequence in which our perceptions might happen to arrive.

Here, Kant suggested that what he had previously called the “exposition of appearances” is the process of determining a definite order and position for occurrences in time. He didn’t specify whether these occurrences are mental representations in a subject or actual states of objects. But in either case, to order them in time means to determine whether, at some particular point or during some period, such occurrences follow one another in a specific order or happen at the same time. In order to determine this, Kant held, we have to assume:

• The existence of objects that endure through time – substances.
• The existence of definite patterns of causation and interaction among them. Thus, he concluded, we need to use the fundamental categories of substance, causation, and interaction for any kind of time-determination, or for the “exposition of appearances” (making coherent sense of experienced events in an ordered way).

Kant did not explain in detail in these notes why we must use these categories to achieve this ordering of experience. A fuller explanation of that would have to wait for the section of the published Critique of Pure Reason called the “Analogies of Experience.” In the Critique, the “Analogies” come after a separate argument for the universal and necessary validity of the categories. This earlier, more abstract argument is based on certain general conceptions of both objects and apperception (self-consciousness) and is called the “Transcendental Deduction of the Pure Concepts of the Understanding.” Since, in Kant’s original sketches of the central argument for his planned Critique, there was no clear separation between the discussion of apperception, objects, and the “exposition of appearances” (and the original discussion of apperception and objects already had the form of an analogy), it is an enduring question for interpreters of the Critique whether or not these two sections (the Transcendental Deduction and the Analogies) ended up separating considerations that should have remained joined. This is a question for any reader of the Critique to consider when trying to analyze the relation between these two key parts.

Developing the Structure (1776–1777)

These thoughts seem to be as far as Kant had progressed by 1775. In several further extensive notes from around 1776–1777, we find for the first time what looks like an outline for a whole intended book. In the first of these notes, Kant divided his plan under four headings:

1. “Dialectic of Sensibility”
2. “Dialectic of Understanding – Transcendental Theory of Magnitude”
3. “Transcendental Theory of Appearance – Reality and Negation”
4. “Transcendental Theory of Experience”

This fourfold division does not, however, imply as elaborate a plan for the work as it might seem. This is because the first three headings all essentially cover the same ground: Kant’s theory of space and time, largely as he had already stated it in the 1770 Inaugural Dissertation. The fourth part then adds to this a statement of the three principles of experience involving the concepts of substance, causation, and interaction (which he had first clearly listed in an earlier note, R 4681). Furthermore, despite the fact that the first three sections all have the word “dialectic” in their titles, it is only in the fourth section that Kant explicitly states both “theses” and “antitheses” (the opposing sides of a contradiction) of the kind that we find in the “Transcendental Dialectic” section of the actual Critique. However, he does hint at antinomies (contradictions) in his treatment of space and time in the earlier sections of this outline.

At this point, Kant was still experimenting with the organization of his planned work. But the content that he here imagined including is fairly clear:

• First, regarding space and time, he maintained that “All space and times are parts of larger ones,” and that “All parts of space and time are themselves spaces” and times. This implies that there are no simple (indivisible) parts in space and time, that space and time are continuous, and that space and time are infinite yet unitary (no matter how large a region of space or time is, it is always part of one larger space or time). Kant implies that to understand these claims, we also have to assume that space and time “are nothing real” (meaning they are ideal, forms of our mind).
• Under the title “Dialectic of Understanding – Transcendental Theory of Magnitude,” he further stated that although the nature of our representation of space and time implies that they can be infinitely extended or divided, nevertheless “Infinite space and infinite past time are incomprehensible” (unbegreiflich). This suggests a conflict between how we intuit space and time and how our intellect tries to comprehend them. Kant did not explain how this conflict was to be resolved beyond asserting that “Space and time belong only to the appearances and therefore to the world and not beyond the world.”
• Then Kant turned to the “Transcendental Theory of Experience.” Here he asserted three main theses (claims):
  1. Something as substance, that is matter, neither comes into nor goes out of existence; from nothing comes nothing. In other words, matter is eternal (though it is dependent on something else).
  2. Every condition (state) of the world is a consequence (an effect). For in the continuity of alteration, everything is starting and stopping, and both starting and stopping have a cause.
  3. All appearances together constitute a world and belong to real objects (this is argued against idealism). God as a cause does not belong to this world of appearances. For only through the agreement of our representations with objects do these representations agree with one another and acquire the unity that perceptions must have if they are to be appearances of a world.
• To the first two of these theses, he opposed what he explicitly labeled “antitheses”:
  • For thesis (1) (substance is eternal), the antithesis is: “There is no substance.”
  • For thesis (2) (every event has a cause), the antithesis is: “Then there would be no first cause.” Kant was not yet clear in this note about the source of the conflict between these theses and antitheses, although the whole note seems to suggest a conflict between the infinite structure of space and time and the demands or needs of the understanding.

The next note gives a clearer picture of the sources of this dialectical conflict. It also suggests that the whole content of the Critique could be organized around this conflict.

• Kant began by explicitly formulating for the first time a principle that would be crucial in the Critique: “The principles of the possibility of experience (of distributive unity) are at the same time the principles of the possibility of the objects of experience.” (This means that the rules that make experience possible for us are also the rules that structure the very objects we experience.)

• He then suggested that there are two classes of such principles:

  1. Principles of “Unity of intuition,” or principles of “appearance” as such.
  2. The principles of “experiences,” or those principles according to which “the existence of appearances is given.”

• Finally, he suggested how antinomies (contradictions) arise: We get one set of principles from the “empirical use of reason,” where the concepts of reason are applied to “space and time as conditions of appearance.” These are called immanent principles because they stay within the bounds of possible experience. We get a different set of principles from the “pure use of reason,” where space and time are not taken to be conditions limiting the use of the concepts of reason. These are transcendent principles because they try to go beyond experience.

• On this basis, Kant described two sets of competing principles that clearly lead directly to the “Antinomy of Pure Reason” section later expounded in the Critique:

  Immanent principles of the empirical use of understanding:

  1. There is no bound (limit) to the composition (building up) and decomposition (breaking down) of appearances.
  2. There is no first ground (ultimate basis) or first beginning.
  3. Everything is mutable (changeable) and variable, thus empirically contingent (it could be otherwise), since time itself is necessary but nothing is necessarily attached to any particular time.

  Transcendent principles of the pure use of understanding:

  1. There is a first part, namely the simple, as the principle of composition, and there are limits to all appearances taken together.
  2. There is an absolute spontaneity, transcendental freedom (an uncaused cause).
  3. There is something which is necessary in itself, namely the unity of the highest reality, in which all the multiplicity of possibilities can be determined through limits…

The first pair of principles from each group (immanent vs. transcendent) stakes out the debate that would later be separated into the First and Second Antinomies in the Critique. These are the disputes over whether space and time (and thus the world) are infinite or finite in extent, and whether they are infinitely divisible or composed of simple parts. The second pair corresponds to the Third Antinomy in the Critique, which debates whether all events have an antecedent (prior) cause or whether there is a first cause (freedom) that has no antecedent cause of its own. The third pair parallels the later Fourth Antinomy, which debates whether the whole series of events in the world is contingent (could have been otherwise) or has an external ground that makes it necessary (a necessary being).

However, the conclusion that Kant drew from this presentation of the antinomies in his 1776-77 notes was not yet what he would later argue in the published Critique.

• He clearly suggested that the “transcendent principles” (which would become the “theses” in the later antinomies, e.g., “the world has a beginning”) arise from using concepts of the understanding without space and time as limiting conditions.
• The “immanent principles” (which would become the “antitheses,” e.g., “the world has no beginning”) result from applying the concepts of the understanding to space and time and using them within the conditions imposed by the structure of our representations of space and time—using them as “principles of the exposition of appearances.”
• But at this stage, he did not reject the “transcendent” use of the concepts of the understanding. On the contrary, he still seemed to hold, as he did in the 1770 Inaugural Dissertation, that there is a legitimate transcendent use of the concepts of the understanding that is unrestricted by the conditions of space and time, and can yield metaphysical knowledge.
• Thus, he reiterated the three “subreptic axioms” (mistaken assumptions to avoid) from the Dissertation, now calling them three “Rules of Dialectic”:
  1. Do not judge what does not belong to appearances (e.g., God) in accordance with rules of appearance (e.g., by applying rules of space and time to God).
  2. Do not subject what does not belong to outer appearance (e.g., spirit) to the conditions of outer appearance.
  3. Do not hold to be impossible what cannot be conceived and represented in intuition (e.g., the totality of the infinite, or of infinite division).
• Then he listed four “principles of the absolute unity of reason” that he apparently thought could be maintained as long as we do not violate any of these three rules: a. Simplicity of the thinking subject (the soul). b. Freedom as the condition of rational actions. c. Ens originarium (the Original Being, or God) as the substratum (underlying basis) of all connection of one’s representations in a whole. d. Do not confuse the restriction of the world (regarding its origin and content) with its limitation (its boundaries).

At this point, then (around 1777), it seems as if Kant envisioned the Critique would include:

1. An account of the nature and structure of space and time, similar to that in the 1770 Dissertation (i.e., they are transcendentally ideal pure forms of intuition).
2. A new account of the use of a priori concepts of the understanding. According to this, these concepts yield “immanent principles for the empirical use of the understanding” only when applied to the conditions of spatiotemporal representation to achieve an “exposition of appearances” (an ordered experience).
3. However, he also seemed to continue to adhere to the view of the Dissertation that these same concepts can also yield transcendent or metaphysical knowledge when they are freed from the restriction of the forms of sensibility.

Perhaps this last point—that concepts could still yield transcendent knowledge—was only a momentary lapse or an unresolved tension in his thought. This is because in the very next preserved note, Kant says something different:

• “The transcendent principles are principles of the subjective unity of cognition through reason, i.e. of the agreement of reason with itself.”
• “Objective principles are principles of a possible empirical use.” This suggests that whatever the exact use of the transcendent principles of pure reason is, it is not to obtain any knowledge of external objects. Knowledge of external objects can only be achieved through the empirical use of the concepts of understanding—their application to representations in space and time for the “exposition of appearances.”

Kant continued with this thought in the following note. Here, he laid out four conflicts between “principles of the exposition of appearances” (principles applied to “appearances” for the “unity of experience”) on the one hand, and “principles of rationality or comprehension” on the other. These conflicts correspond precisely to the four antinomies of the Critique. The first set of principles (for the exposition of appearances) is:

1. No absolute totality in composition (building up parts into wholes), hence infinite progress.
2. No absolute totality of decomposition (breaking wholes into parts), hence nothing absolutely simple.
3. No absolute totality of the series of generation (causes and effects), hence no unconditioned spontaneity (no uncaused first action).
4. No absolute necessity.

The opposing set of “principles of rationality” is:

1. Unconditioned totality of the dependent whole.
2. Unconditioned simple.
3. Unconditioned spontaneity of action.
4. Unconditioned necessary being.

Kant then said that these latter “propositions [the principles of rationality] are subjectively necessary as principles of the use of reason in the whole of cognition: [for the] unity of the whole of the manifold of cognition of the understanding. They are practically necessary with regard to…” Unfortunately, he did not finish this thought in the note, or explain the “practical necessity” of these principles of reason at this point. But he was clearly drawing back from the idea that reason by itself furnishes metaphysical knowledge of real objects that are independent of our own thought.

Summing up the results so far, then, it looks as if by 1777 Kant had come this far in planning the Critique of Pure Reason:

1. It would include the account of space and time as transcendentally ideal pure forms of intuition, an idea already reached in 1770.
2. It would include a derivation of three concepts of the understanding—substance, causation, and interaction—and their associated principles. These would be shown as necessary for the “exposition of appearances” given through the forms of space and time, and as objectively valid only in that context.
3. It would include a presentation in the form of a four-part antinomy. This antinomy would pit those principles that are valid for the exposition of appearances against four opposed transcendent principles. These transcendent principles use the concepts of understanding but without the restriction of the forms of sensibility. Kant seemed to think these transcendent principles have no objective validity (they don’t give knowledge of objects) but can be used in some unspecified way for the unification of empirical knowledge and for some equally unspecified practical purpose.

Such a Critique would basically have consisted of a theory of sensibility, a theory of experience, and an antinomy of pure reason.

Clearly, Kant needed more time to understand the positive function of pure reason, which was only hinted at in these notes from 1777. But this is not the only way that the outline of the Critique that we can construct for the period around 1777 differs from the work as it was finally published. There are several other glaring differences.

One idea Kant suggested to explain how categories become necessary is this:

• To link appearances into an orderly experience that belongs to a unified mind or self-consciousness, certain principles must be imposed on those appearances.
• These principles arise because we necessarily have to think about a unified mind—what Kant then started to call “apperception” (or self-perception)—in a particular way.
• He stated: “Whatever is to be thought as an object of perception stands under a rule of apperception, or self-perception.”
• He then claimed there is a “threefold dimension of synthesis” because there are “three functions of apperception,” or three ways we conceive of ourselves. We necessarily think of our own thoughts as:
  1. Having a “relation to a subject” (meaning, they are my thoughts).
  2. Having a “relation of succession among each other” (they occur one after another).
  3. “[Comprising] a whole” (they form a unified stream of experience).
• Because we conceive of our own unified consciousness in these ways, Kant suggested, we therefore impose these same kinds of relational structures—which he would later identify as the categories of relation (substance, causality, and community/interaction)—onto the objects we represent.
• Following this line of argument, Kant said, “I am the original of all objects.” This means he thought we understand objects by analogy with the way we must understand our own unified self.

Alternatively, Kant sometimes suggested the reverse:

• We necessarily think about objects using categories such as a “subject” (or substance) which has a “succession” of states and forms a “whole” of properties.
• Then, we understand ourselves and the unity of our own thoughts by analogy to how we necessarily think about objects.
• For instance, in another note, he argued: “All existence belongs to a substance; everything that happens is a member of a series; everything that is simultaneous belongs to a whole whose parts reciprocally determine each other.” He then suggested that the way we conceive of ourselves, as subjective orders of experience, corresponds to these fundamental ways of conceiving of objects.

In some of his most promising remarks from this period, however, Kant suggested that there might be direct arguments showing why certain categories of the understanding are necessary for specific time-determinations. These arguments would not need to rely on analogies between how we think of the self and how we think of objects, in either direction.

• Thus, Kant argued that to assign definite positions to events in time, we need a framework of principles. These principles use the same categories (substance, causality, community/interaction) that in other passages he had associated with the concept of a subject or an object.
• His notes from this time suggest ideas along these lines (though often expressed very densely):
  • For an event to occur, something must precede it. Among the many things that could come before an event, there is one from which the event always follows (this points towards the category of causality).
  • For any point in time to be determined, and for something real to be associated with it, there must be something that accompanies it and helps to determine that point in time. Among the many things that can accompany it, something must always be there (this points towards an enduring substance).
  • For things to be considered simultaneous (happening at the same time), there must be a connection between them, a mutual determination of these various things by one another (this points towards reciprocal interaction, or community).
  • If there were not something that always existed—something permanent and stable (a substance)—there would be no firm reference point for determining moments in time. Thus, there would be no definite perception, meaning no way to determine something as being at a specific point in time.
  • If there were not something that always preceded an occurrence (a cause), then among the many things that come before an event, the event would not have a definite place in a series of events.
  • Through such “rules of perception” (which involve these categories), the objects of our senses become determinable in time. In raw intuition (our direct sensing), objects are merely given as appearances. These rules, applied by the understanding, help to establish an objective order for these appearances, an order that is different from the mere subjective sequence in which our perceptions might happen to arrive.

Here, Kant suggested that what he had previously called the “exposition of appearances” is the process of determining a definite order and position for occurrences in time. He didn’t specify whether these occurrences are mental representations in a subject or actual states of objects. But in either case, to order them in time means to determine whether, at some particular point or during some period, such occurrences succeed one another in a specific order or happen at the same time (are simultaneous). In order to make these determinations, Kant held, we have to assume:

• The existence of objects that endure through time – substances.
• The existence of definite patterns of causation and interaction among them. Thus, he concluded, we need to use the fundamental categories of substance, causation, and interaction for any kind of time-determination, or for the “exposition of appearances” (making coherent sense of experienced events in an ordered way).

Kant did not explain in detail in these notes why we must use these categories to accomplish this end. A fuller explanation of that would have to wait for the section of the published Critique of Pure Reason called the “Analogies of Experience.” In the Critique, the “Analogies” appear after a separate argument for the universal and necessary validity of the categories. This earlier, more abstract argument is based on certain general conceptions of both objects and apperception (self-consciousness) and is called the “Transcendental Deduction of the Pure Concepts of the Understanding.” Since, in Kant’s original sketches of the central argument for his planned Critique, there was no clear separation between the discussion of apperception, objects, and the “exposition of appearances” (and the original discussion of the relation between apperception and objects already had the form of an analogy), it is an enduring question for interpreters of the Critique whether these two sections (the Transcendental Deduction and the Analogies) ended up separating considerations that should have remained joined. This is a question for any reader of the Critique to consider when trying to analyze the relation between these two key parts.

Refining the Structure (1776–1777)

These thoughts seem to be as far as Kant had progressed by 1775. In several further extensive notes from around 1776–1777, we find for the first time what looks like an outline for a whole intended book. In the first of these notes, Kant divided his plan under four headings:

1. “Dialectic of Sensibility”
2. “Dialectic of Understanding – Transcendental Theory of Magnitude”
3. “Transcendental Theory of Appearance – Reality and Negation”
4. “Transcendental Theory of Experience”

This fourfold division does not, however, imply as elaborate a plan for the work as it might seem. This is because the first three headings all essentially cover the same ground: Kant’s theory of space and time, largely as he had already stated it in the 1770 Inaugural Dissertation. The fourth part then adds to this a statement of the three principles of experience involving the concepts of substance, causation, and interaction. Furthermore, despite the fact that the first three sections all have the word “dialectic” in their titles, it is only in the fourth section that Kant explicitly stated both “theses” and “antitheses” (the opposing sides of a contradiction) of the kind that we find in the “Transcendental Dialectic” section of the actual Critique. However, he did hint at antinomies (contradictions) in his treatment of space and time in the earlier sections of this outline.

At this point, Kant was still experimenting with the organization of his planned work. But the content that he here imagined including is fairly clear:

• First, regarding space and time, he maintained that “All space and times are parts of larger ones,” and that “All parts of space and time are themselves spaces” and times. This implies that there are no simple (indivisible) parts in space and time, that space and time are continuous, and that space and time are infinite yet unitary (no matter how large a region of space or time is, it is always part of one larger space or time). Kant implies that to understand these claims, we also have to assume that space and time “are nothing real” (meaning they are ideal, forms of our mind).
• Under the title “Dialectic of Understanding – Transcendental Theory of Magnitude,” he further stated that although the nature of our representation of space and time implies that they can be infinitely extended or divided, nevertheless “Infinite space and infinite past time are incomprehensible” (unbegreiflich). This suggests a conflict between how we intuit space and time and how our intellect tries to comprehend them. Kant did not explain how this conflict was to be resolved beyond asserting that “Space and time belong only to the appearances and therefore to the world and not beyond the world.”
• Then Kant turned to the “Transcendental Theory of Experience.” Here he asserted three main theses (claims):
  1. Something as substance (that is, matter) neither comes into existence nor goes out of existence; from nothing comes nothing. In other words, matter is eternal (though it is dependent on something else).
  2. Every condition (state) of the world is a consequence (an effect). For in the continuity of alteration, everything is starting and stopping, and both starting and stopping have a cause.
  3. All appearances together constitute a world and belong to real objects (this is argued against idealism). God, as a cause, does not belong to this world of appearances. For only through the agreement of our representations with objects do these representations agree with one another and acquire the unity that perceptions must have if they are to be appearances of a world.
• To the first two of these theses, he opposed what he explicitly labeled “antitheses”:
  • For thesis (1) (substance is eternal), the antithesis is: “There is no substance.”
  • For thesis (2) (every event has a cause), the antithesis is: “Then there would be no first cause.” Kant was not yet clear in this note about the source of the conflict between these theses and antitheses, although the whole note seems to suggest a conflict between the infinite structure of space and time and the demands or needs of the understanding.

The next note gives a clearer picture of the sources of this dialectical conflict. It also suggests that the whole content of the Critique could be organized around this conflict.

• Kant began by explicitly formulating for the first time a principle that would be crucial in the Critique: “The principles of the possibility of experience… are at the same time the principles of the possibility of the objects of experience.” (This means that the rules that make experience possible for us are also the rules that structure the very objects we experience.)

• He then suggested that there are two classes of such principles:

  1. Principles of “Unity of intuition,” or principles of “appearance” as such.
  2. The principles of “experiences,” or those principles according to which “the existence of appearances is given.”

• Finally, he suggested how antinomies (contradictions) arise: We get one set of principles from the “empirical use of reason,” where the concepts of reason are applied to “space and time as conditions of appearance.” These are called immanent principles because they stay within the bounds of possible experience. We get a different set of principles from the “pure use of reason,” where space and time are not taken to be conditions limiting the use of the concepts of reason. These are transcendent principles because they try to go beyond experience.

• On this basis, Kant described two sets of competing principles that clearly lead directly to the “Antinomy of Pure Reason” section later expounded in the Critique:

  Immanent principles of the empirical use of understanding:

  1. There is no bound (limit) to the composition (building up) and decomposition (breaking down) of appearances.
  2. There is no first ground (ultimate basis) or first beginning.
  3. Everything is mutable (changeable) and variable, thus empirically contingent (it could be otherwise), since time itself is necessary but nothing is necessarily attached to any particular time.

  Transcendent principles of the pure use of understanding:

  1. There is a first part, namely the simple, as the principle of composition, and there are limits to all appearances taken together.
  2. There is an absolute spontaneity, transcendental freedom (an uncaused cause).
  3. There is something which is necessary in itself, namely the unity of the highest reality, in which all the multiplicity of possibilities can be determined through limits…

The first pair of principles from each group (immanent vs. transcendent) stakes out the debate that would later be separated into the First and Second Antinomies in the Critique. These are the disputes over whether space and time (and thus the world) are infinite or finite in extent, and whether they are infinitely divisible or composed of simple parts. The second pair corresponds to the Third Antinomy in the Critique, which debates whether all events have an antecedent (prior) cause or whether there is a first cause (freedom) that has no antecedent cause of its own. The third pair parallels the later Fourth Antinomy, which debates whether the whole series of events in the world is contingent (could have been otherwise) or has an external ground that makes it necessary (a necessary being).

However, the conclusion that Kant drew from this presentation of the antinomies in his 1776-77 notes was not yet what he would later argue in the published Critique.

• He clearly suggested that the “transcendent principles” (which would become the “theses” in the later antinomies, e.g., “the world has a beginning”) arise from using concepts of the understanding without space and time as limiting conditions.
• The “immanent principles” (which would become the “antitheses,” e.g., “the world has no beginning”) result from applying the concepts of the understanding to space and time and using them within the conditions imposed by the structure of our representations of space and time—using them as “principles of the exposition of appearances.”
• But at this stage, he did not reject the “transcendent” use of the concepts of the understanding. On the contrary, he still seemed to hold, as he did in the 1770 Inaugural Dissertation, that there is a legitimate transcendent use of the concepts of the understanding that is unrestricted by the conditions of space and time, and can yield metaphysical knowledge.
• Thus, he reiterated the three “subreptic axioms” (mistaken assumptions to avoid) from the Dissertation, now calling them three “Rules of Dialectic”:
  1. Do not judge what does not belong to appearances (e.g., God) in accordance with rules of appearance (e.g., by applying rules of space and time to God).
  2. Do not subject what does not belong to outer appearance (e.g., spirit) to the conditions of outer appearance.
  3. Do not hold to be impossible what cannot be conceived and represented in intuition (e.g., the totality of the infinite, or of infinite division).
• Then he listed four “principles of the absolute unity of reason” that he apparently thought could be maintained as long as we do not violate any of these three rules: a. Simplicity of the thinking subject (the soul). b. Freedom as the condition of rational actions. c. Ens originarium (the Original Being, or God) as the substratum (underlying basis) of all connection of one’s representations in a whole. d. Do not confuse the restriction of the world (regarding its origin and content) with its limitation (its boundaries).

At this point, then (around 1777), it seems as if Kant envisioned the Critique would include:

1. An account of the nature and structure of space and time, similar to that in the 1770 Dissertation (i.e., they are transcendentally ideal pure forms of intuition).
2. A new account of the use of a priori concepts of the understanding. According to this, these concepts yield “immanent principles for the empirical use of the understanding” only when applied to the conditions of spatiotemporal representation to achieve an “exposition of appearances” (an ordered experience).
3. However, he also seemed to continue to adhere to the view of the Dissertation that these same concepts can also yield transcendent or metaphysical knowledge when they are freed from the restriction of the forms of sensibility.

Perhaps this last point—that concepts could still yield transcendent knowledge—was only a momentary lapse or an unresolved tension in his thought. This is because in the very next preserved note, Kant says something different:

• “The transcendent principles are principles of the subjective unity of cognition through reason, i.e. of the agreement of reason with itself.”
• “Objective principles are principles of a possible empirical use.” This suggests that whatever the exact use of the transcendent principles of pure reason is, it is not to obtain any knowledge of external objects. Knowledge of external objects can only be achieved through the empirical use of the concepts of understanding—their application to representations in space and time for the “exposition of appearances.”

Kant continued with this thought in the following note. Here, he laid out four conflicts between “principles of the exposition of appearances” (principles applied to “appearances” for the “unity of experience”) on the one hand, and “principles of rationality or comprehension” on the other. These conflicts correspond precisely to the four antinomies of the Critique. The first set of principles (for the exposition of appearances) is:

1. No absolute totality in composition (building up parts into wholes), hence infinite progress.
2. No absolute totality of decomposition (breaking wholes into parts), hence nothing absolutely simple.
3. No absolute totality of the series of generation (causes and effects), hence no unconditioned spontaneity (no uncaused first action).
4. No absolute necessity.

The opposing set of “principles of rationality” is:

1. Unconditioned totality of the dependent whole.
2. Unconditioned simple.
3. Unconditioned spontaneity of action.
4. Unconditioned necessary being.

Kant then said that these latter “propositions [the principles of rationality] are subjectively necessary as principles of the use of reason in the whole of cognition: [for the] unity of the whole of the manifold of cognition of the understanding. They are practically necessary with regard to…” Unfortunately, he did not finish this thought in the note, or explain the “practical necessity” of these principles of reason at this point. But he was clearly drawing back from the idea that reason by itself furnishes metaphysical knowledge of real objects that are independent of our own thought.

Summing up the results so far, then, it looks as if by 1777 Kant had come this far in planning the Critique of Pure Reason:

1. It would include the account of space and time as transcendentally ideal pure forms of intuition, an idea already reached in 1770.
2. It would include a derivation of three concepts of the understanding—substance, causation, and interaction—and their associated principles. These would be shown as necessary for the “exposition of appearances” given through the forms of space and time, and as objectively valid only in that context.
3. It would include a presentation in the form of a four-part antinomy. This antinomy would pit those principles that are valid for the exposition of appearances against four opposed transcendent principles. These transcendent principles use the concepts of understanding but without the restriction of the forms of sensibility. Kant seemed to think these transcendent principles have no objective validity (they don’t give knowledge of objects) but can be used in some unspecified way for the unification of empirical knowledge and for some equally unspecified practical purpose.

Such a Critique would basically have consisted of a theory of sensibility, a theory of experience, and an antinomy of pure reason.

Clearly, Kant needed more time to understand the positive function of pure reason, which was only hinted at in these notes from 1777. But this is not the only way that the outline of the Critique that we can construct for the period around 1777 differs from the work as it was finally published. There are several other glaring differences.

First, the “transcendental theory of experience,” or the theory of the “immanent use” of the concepts of understanding, was not yet divided into two distinct parts:

1. A transcendental deduction of the categories (a proof of their validity).
2. A derivation of the principles of judgment used in the “exposition of appearances” (like the Analogies of Experience). This separation is present in the published work.

Second, all of these notes from around 1777 suggest that the content of the “Dialectic” section of the Critique would be entirely covered by the four antinomies of pure reason. However, in the published Critique, the Dialectic is divided into three main parts:

1. The “Paralogism” (dealing with illusions about the self or soul).
2. The “Antinomy” (dealing with contradictions about the world as a whole).
3. The “Ideal of Pure Reason” (dealing with illusions about God).

Can we learn anything about what led to these further divisions of the Critique before it finally took on the form Kant gave it in 1779 and 1780?

Finalizing the Structure (1778–1780)

Fortunately, some notes assigned to the period 1776–1778 (rather than just 1775–1777) survive and shed light on the final development of Kant’s conception of the Critique. In one note that has been assigned to the later part of this period (1778-1780), Kant for the first time suggested that there might be a deduction of the categories as necessary conditions of apperception (the unity of consciousness) that does not depend upon the temporal character of the data to be unified. Since this may be the earliest surviving sketch of a Transcendental Deduction conceived of as separate from, and prior to, the argument that shows the categories are conditions for the possibility of the “exposition of appearances” (what Kant would later call the “Analogies of Experience”), it is worth quoting this passage from his notes in full: “In everything passive or what is given, apprehension [the mind’s taking in of information] must not merely be found, but it must also be necessitated [made necessary] in order to represent it as given, i.e., the individual apprehension must be determined by the universal. The universal is the relation to the others and to the whole of the state. By being distinguished from the arbitrary is it considered as given, and only by being subsumed under the categories is it considered as something. It must therefore be represented in accordance with a rule by which appearance becomes experience and by which the mind comprehends it as one of its actions of self-consciousness, within which, as in space and time, all data are to be encountered. The unity of the mind is the condition of thinking, and the subordination of every particular under the universal is the condition of the possibility of associating a given representation with others through an action. Even if the rule is not immediately obvious, nevertheless one must represent the object as amenable to a rule in order to conceive it as that which represents something, i.e., something which has a determinate position and function among the other determinations. …” This note, which is very similar to a crucial passage in the version of the “Transcendental Deduction” published in the first edition of the Critique, is notable for two reasons.

On the one hand, it clearly suggests that there must be general rules for the unity of consciousness that can be characterized independently of specific rules for ordering things in time. However, the way remains open for a further inference: once the temporal character of the data for consciousness is considered, then these general rules may lead to further rules which are themselves specifically temporal in content. Such a separation—between the most general rules for the unity of consciousness and the specific rules for the unity of a consciousness that is temporal in character—along with the necessity of explaining the relation between these two kinds of rules, would become central to the organization of the Critique of Pure Reason. In the Critique, Kant would offer:

1. A transcendental deduction of the pure concepts of the understanding (the categories) as conditions for the possibility of any unity of consciousness in general. This would be under the heading of an “Analytic of Concepts.”
2. A derivation from those general rules of more specific rules for time-determination. This would be under the heading of a “Schematism of the Pure Concepts of the Understanding.”
3. The “Schematism,” in turn, would be part of the “Analytic of Principles.” In this part, Kant would argue for specific principles involving the temporally interpreted categories (such as the principles of the conservation of substance and of universal causation) as necessary conditions for objective time-determination. The introduction of the concept of schematism—which Kant first recorded in a note from 1778–1779 with the statement that “We must subject all of our pure concepts of the understanding to a schema, a way of putting the manifold [of intuition] together in space and time”—was required precisely by this explicit separation between the transcendental deduction of the categories and the “Analogies of Experience” (and related arguments) by means of which Kant had previously derived the categories (more directly from the needs of time-determination).

On the other hand, this note from 1778-80 also reveals a fundamental ambivalence or ambiguity about exactly how the categories are to be derived from the general idea of the “unity of consciousness.” This ambiguity continued one already found in Kant’s materials from 1775.

• In one strategy, rules (categories) are necessary to distinguish an arbitrary series of representations from the orderly or rule-governed series of representations by means of which a determinate object is presented to consciousness. On this account, the “unity of consciousness” would mean the unity of consciousness characteristic of the presentation of an object.
• Alternatively, Kant suggested that rules are necessary for the unity of consciousness as a form of self-consciousness—the recognition that various representations, whatever objects they may or may not represent, all have the unity of belonging to a single mind. Kant did not clearly separate these two strategies, nor did he suggest a clear means for connecting them. This ambiguity would plague all of Kant’s attempts to find a definitive form for the deduction of the categories. It runs throughout the first-edition version of the “Transcendental Deduction.” It then led Kant to continue to experiment with the proper form for the deduction, not merely in the second edition of the Critique (in which he completely rewrote the “Deduction”), but also in the period between the two editions. During that time, he tried to resolve the ambiguity in the Prolegomena to Any Future Metaphysics (1783), the Metaphysical Foundations of Natural Science (1786), and a number of surviving drafts. He continued to tinker with the deduction on into the 1790s as well, in his drafts for an essay on the Real Progress of Metaphysics from the Time of Leibniz and Wolff. Arriving at a definitive interpretation of the transcendental deduction of the categories has been the most difficult task for Kant scholarship throughout the 20th century, and this underlying ambivalence in Kant’s conception of its strategy is a large part of the reason for this problem.

Kant never completely resolved the issue of the fundamental strategy for the deduction of the categories. However, much else about the content and structure of the Critique had clearly been resolved by 1778–1779. Several extensive drafts from this period show that Kant had not only arrived at the final organization of the “Transcendental Analytic,” but also that he had now arrived at the final organization of the “Transcendental Dialectic.” The Dialectic’s structure was also now more complicated than the schemes he had been considering in the period 1775–1777. Whereas in the notes from that earlier period Kant presented the material of the “Dialectic” as a single set of antinomies, now he had divided the material into three main parts, diagnosing “three kinds of transcendental illusion” generated by “three kinds of rational inference.” Thus, at this point (around 1778-79), Kant envisioned the following overall argument for his book.

The constructive argument of the book would consist of two main parts. The first of these main parts (which would become the “Doctrine of Elements”) would in turn be broken into two further parts:

1. First would be the account of space and time that had been in place since 1770. In the Critique, Kant would finally entitle this the “Transcendental Aesthetic.”
2. Then, in the second part, under the title of “Transcendental Analytic” (which he now introduced), Kant would make the argument. This argument would be based on the principle (which he now explicitly formulated) that “We can have synthetic cognition a priori about objects of experience, if [this cognition] consists of principles of the possibility of experience.” In the Analytic, a transcendental deduction of the categories would be linked to a demonstration of their role in empirical time-determination by means of an intervening schematism of those categories. This whole argument—showing that the categories must be applied to representations given in space and time in order to yield unity of consciousness and objective experience of objects—would have the consequence that by means of these concepts “we cognize only objects of the senses.” Thus, the categories “do not reach to the supersensible” (things beyond sense experience).

It would then be the burden of the second main part of the work—which Kant had already been referring to as a “Dialectic” for some years—to show that:

• “Even though the concepts [of the pure understanding] extend to all objects of thought in general,”
• “they do not yield any amplification [increase] of theoretical cognition” beyond experience.
• However, they may nevertheless have a “practical-dogmatic” role in a “practical regard [context], where freedom is the condition of their use.”

Now, Kant divided this critical part of the work (the Dialectic) into three divisions. He argued that it is characteristic of pure reason to assume as a “petition” or “postulate” the principle that “All conditioned cognition not only stands under conditions, but finally under one which is itself unconditioned,” or, put another way, “If the conditioned is given, then the entire series of all its conditions is also given.” (Reason naturally seeks ultimate, complete explanations that don’t depend on anything further). He now argued that because there are three kinds of rational inference (from a property to its subject; from a property to another property; and from a property to its ground), there must be three corresponding “dialectical inferences” (faulty logical leaps) back to:

• An unconditioned or absolute substance (the soul).
• An unconditioned or absolute whole (the world-series).
• An unconditioned or absolute ground (God). Thus, reason postulates “the unconditioned subjective conditions of thinking [the self/soul], the unconditioned (objective) condition of appearances [the world as a complete series], and the unconditioned objective condition of all things in general [God].” These three kinds of inferences, which Kant would discuss in the Critique under the titles of the “Paralogism” (about the soul), the “Antinomy” (about the world), and the “Ideal of Pure Reason” (about God), would be diagnosed as theoretically unjustified. This is because the underlying principle—that whenever the conditioned is given, so is its ultimate unconditioned ground—is itself theoretically unjustified when applied beyond possible experience. Nevertheless, Kant would argue, these three ideas of the unconditioned will be useful in a practical (moral) context.

Even in the published Critique, Kant would retain the argument that the three forms of “transcendental illusion” arise from three forms of (misapplied) inference. However, he also suggested both in these notes from 1778-79 and in the published work that these illusions arise directly from an unwarranted reification of the three concepts of a subject, a series, and a ground. (Reification means treating an abstract concept as if it were a concrete, real thing). It is easier to understand his diagnosis in these terms. Thus, the three fundamental errors of traditional metaphysics are the assumptions that:

1. Because we assign all of our thoughts to our selves as subjects, we therefore have knowledge of the soul as an absolute subject (a simple, enduring substance).
2. Because we place all appearances in various series (of ever-increasing or ever-decreasing spaces and times; of causes and effects; of contingent things depending on other things), we therefore have knowledge of completed series or wholes (such as a completed extension of the world in space and time, of ultimate simple parts of matter, of a first uncaused cause, or of an absolutely necessary ground for all contingent things).
3. Because we must think of some ground for any possibility, we therefore have knowledge of an absolute ground of all possibilities (God as the most real being). In Kant’s words from his notes:

• “The idea of the soul is grounded on [the idea that] the understanding must relate all thoughts and inner perceptions to the self and assume this as the only permanent subject.”
• “The idea of the unconditioned for all conditions in appearance is grounded in reason as the prescription to seek the completeness of all cognition of the understanding in [series of] subordination.”
• “The idea of the unconditioned unity of all objects of thought in an ens entium [Being of beings, i.e., God] is necessary in order to seek the relationship among all possible [things]…”

Kant suggests that it is natural for us to form these ideas, and that there is even a subjective necessity to do so. However, it is a mistake to interpret them as offering theoretical knowledge of objects of a kind that could never be presented by our senses.

What led Kant to divide his diagnosis of metaphysical illusions concerning the self, the world, and God into these three distinct parts (rational psychology, rational cosmology, and rational theology)? Previously, claims about the soul were simply instances within the general Antinomies (e.g., the simplicity of the soul was just an instance of simplicity in general, and the freedom of the self was an instance of absolute spontaneity). Also, an absolutely necessary ground for all contingent things was the subject of the Fourth Antinomy.

• The contents of the third part of the “Dialectic” in the published Critique, the “Ideal of Pure Reason,” suggest that Kant elevated the discussion of rational theology into a separate section simply because he had too much material to treat it as a single antinomy. In this section, he recapitulates his critique of the ontological, cosmological, and physico-theological arguments for God’s existence from his 1763 work, The Only Possible Ground. He also criticizes his own positive argument from that earlier work. This is all in addition to retaining the arguments about a necessary being that constitute parts of the Third and Fourth Antinomies in the Critique. Kant would also have found it difficult to integrate his positive account of how reason necessarily generates an “ideal of pure reason” into any discussion that takes the form of an antinomy.

• The criticism of rational psychology in the “Paralogism” section, however, is something new, which appears in these notes of 1778–1779 for the first time. Here, one can conjecture that the new “Paralogism” section is Kant’s response to his own new transcendental deduction of the categories. Because he had claimed that the unity of consciousness is an a priori necessity from which we can deduce the validity of the categories, he now also had to tell us to be careful what not to infer from this unity of consciousness. Specifically, we should not infer any metaphysical claims about the soul—claims that the subject or bearer of consciousness is a unitary, simple, and eternal substance. Such a “paralogism of pure reason” would really be “a transcendental subreption”—an illusion in which “the unity of apperception, which is subjective, would be taken for the unity of the subject as a thing.” We find no such warning in Kant before we find the introduction of a separate transcendental deduction of the categories from the unity of consciousness. So, we can assume that the expansion of the “Dialectic” to include paralogisms of pure reason (separate from the earlier Antinomy discussions of the soul’s properties) was a cautionary response to his new deduction—Kant’s own warning about what not to read into his argument about the unity of consciousness. Then, once the structure of the “Dialectic” had been expanded in this way, it would not have been unnatural for Kant to also add a fuller treatment of theoretically unjustified (though potentially morally useful) conceptions of God as well.

One last note, written on a matriculation record from March 1780 (and thus either a final draft for the Critique which was about to be written, or a memo written during its composition), recapitulates much of this outline. It then adds a reference to one final section of the Critique: “To the Canon: the end [ultimate aim] of the whole of metaphysics is God and the future [immortality], and the end [purpose] of these [ideas of God and a future life is found in] our conduct; not as though morality must be arranged in accordance with these [ideas], but because without these [ideas] morality would be without [ultimate] consequences.”

This note is cryptic and can only be fully understood in light of the argument that Kant develops over all three of his Critiques. This argument is that the highest good—the maximization of both virtue and happiness—is something we can only conceive of as being made possible by an intelligent and benevolent Author of the world (God). This Author would also be prepared to give us the time necessary to perfect our virtue (immortality) and to make the world suitable for the achievement of our ends. This belief in God and immortality is not the motivation for virtuous action, but it is presupposed by the ultimate rationality of such action. This is the practical use to which Kant would put the (theoretically unprovable) ideas of metaphysics. Conceiving of a “canon” of pure reason as well as its critique—that is, a doctrine of its positive practical use as well as the negative criticism of its misguided theoretical use—was thus the final stage in Kant’s conception of the structure and content of the Critique of Pure Reason. This “canon” would be expanded into a “Doctrine of Method.” This part would accompany the “Doctrine of Elements,” into which the “Transcendental Aesthetic,” “Transcendental Analytic,” and “Transcendental Dialectic” would be placed.

With all of this in place by 1779 or 1780, Kant was finally able to write the Critique. He announced to Herz on May 1, 1781, after a decade of apologies and postponements, that “In the current Easter book fair there will appear a book of mine, entitled Critique of Pure Reason.” Ten days later, he wrote to Herz these lines: “My work, may it stand or fall, cannot help but bring about a complete change of thinking in this part of human knowledge [metaphysics], a part of knowledge that concerns us so earnestly. For my part I have nowhere sought to create mirages or to advance specious [misleadingly attractive] arguments in order to patch up my system; I have rather let years pass by, in order that I might get to a finished insight that would satisfy me completely and at which I have in fact arrived; so that I now find nothing I want to change in the main theory (something I could never say of any of my previous writings), though here and there little additions and clarifications would be desirable.”

Understanding the Second Edition of Kant’s Critique of Pure Reason

Immanuel Kant wrote the Critique of Pure Reason as a foundation for his larger philosophical ideas. He didn’t see it as the final piece of his work. Instead, he planned it as an essential first step. His main goal was to build a complete system of thought covering both nature and morals. After finishing the Critique, he aimed to write detailed books on these two subjects.

Kant’s Progress and Unexpected Challenges

Kant did make good progress on his larger system.

• In 1786, he published Metaphysical Foundations of Natural Science. In this book, he tried to show how his general ideas about judgment could lead to the basic principles of Newton’s physics, using the concept of motion.
• In 1785, he published Groundwork of the Metaphysics of Morals. This was meant to be the introduction to a detailed system of duties, which would form his philosophy of morals. (This full system, however, didn’t appear until 1797).

But the first reaction to the Critique of Pure Reason deeply disappointed Kant. He had hoped the book would “bring about a complete change of thinking.” It didn’t, at least not immediately. Because of this, Kant spent much of the 1780s doing something he hadn’t planned: explaining and clarifying the core ideas of his Critique. He had thought he had already made these foundations clear when he finished the book in May 1781.

This work of clarification took several forms:

• He published a short defense and simpler explanation of the Critique in 1783, called Prolegomena to any Future Metaphysics.
• He continued to work on a key part of the Critique, the “transcendental deduction,” in his private notes from 1783 to 1784.
• He proposed a revised version of the transcendental deduction in the introduction to his 1786 book, Metaphysical Foundations of Natural Science.
• He significantly revised the Critique of Pure Reason for its second edition in 1787.
• Finally, he published two more major works: the Critique of Practical Reason (1788) and the Critique of Judgment (1790). Kant hadn’t originally planned these books when he first published the Critique of Pure Reason. They grew out of his ongoing efforts to make the foundations of his critical philosophy clearer.

This explanation will focus on the main changes made in the second edition of the first Critique, after briefly mentioning some revisions hinted at in the Prolegomena and Metaphysical Foundations of Natural Science.

The First Major Review and Its Impact

For a year after it was published, the Critique only received two friendly but unimportant reviews. Then, in 1782, it got its first serious review. This review appeared in a supplement to a scholarly journal from the University of Göttingen. This university was known for a group of philosophers who believed that knowledge comes primarily from experience (empiricists), led by J. G. H. Feder.

The review was critical and dismissive. It seems Feder shortened and rewrote a much longer and more positive draft written by Christian Garve, a moral philosopher from Berlin. Feder’s published version left out Garve’s careful explanation of many of Kant’s arguments. It also omitted Garve’s insightful understanding of how Kant justified the possibility of synthetic a priori cognition – knowledge that is new (synthetic) but known before experience (a priori) – especially in mathematics.

Instead, Feder’s review focused on three main objections:

1. It claimed that Kant’s philosophical system, which he called “transcendental idealism,” was just a new version of Berkeley’s idealism. Berkeley was a philosopher who argued that things only exist as ideas in our minds or in God’s mind. The review said Kant reduced all objects to our own sensations. This meant we could never really know if any objects existed beyond our own thoughts.
2. It argued that Kant’s ideas made it impossible to tell the difference “between the actual and the imagined, the merely possible,” or between reality and “mere visions and fantasies.”
3. It charged that Kant’s argument about replacing the flawed theoretical use of pure reason with a sound practical use was unnecessary. The review claimed that morality already had a solid basis in common sense.

Kant’s Response in the Prolegomena

Kant had apparently already decided to write a shorter, more popular version of his critical philosophy almost as soon as the Critique was published. The hostile review clearly motivated him further. He included direct answers to some of its charges in his book Prolegomena to any Future Metaphysics, published in August 1783.

Specifically, Kant addressed the criticisms:

• Distinction from Berkeley’s Idealism: He explained that his position was different from Berkeleian idealism. Kant argued that he denied the real existence of space and time as things in themselves and the properties of objects related to space and time. However, he did not deny the real existence of objects themselves, distinct from our mental representations of them. For this reason, he suggested renaming his “transcendental idealism” to the more informative “formal idealism” or “critical idealism.” This was to make it clear that his idealism was about the form of our knowledge of external objects, not about whether those objects exist.
• Distinguishing Reality from Dreams: He argued that his theory of how the mind understands things, unlike other types of idealism, offered clear principles for telling coherent, real experiences apart from incoherent dreams and fantasies. Because of this, he said his philosophy should not be considered a “higher” idealism (implying it was fanciful or unrealistic). Instead, he described it as a philosophy firmly rooted in “the fruitful bathos of experience,” meaning it was grounded in the richness of actual experience.
• Explaining A Priori Knowledge: Kant also rejected any comparison to Berkeley because Berkeley’s empiricism (the idea that all knowledge comes from experience) means that all knowledge of space and time must come after experience (a posteriori) and is therefore not universally necessary (contingent). Kant argued that only his own formal idealism could explain our a priori knowledge of space and time—our understanding of space and time as universal and necessary ways we perceive everything.

Goals for the Second Edition of the Critique

Making two points clear became major goals for Kant when he revised the Critique for its second edition:

1. Only his transcendental idealism could explain our a priori knowledge of mathematics and pure physics.
2. This formal idealism was entirely compatible with the real existence of external objects.

Another goal for these revisions was to defend his view that the misleading theoretical use of pure reason must be replaced by its sound practical use. This was the third point challenged by the Göttingen review, which he hadn’t addressed in the Prolegomena.

However, just like when his earlier work (the inaugural dissertation) received criticism, Kant also revealed in the Prolegomena a concern that his critic hadn’t actually raised. This was a worry about the strength of the transcendental deduction of the categories itself. The categories are fundamental concepts the mind uses to understand the world.

Kant expressed this worry as gently as he could. He said he was completely satisfied with the “content, order, and doctrine” of his work. But, he added, he was “not entirely satisfied with the presentation in some parts of the Doctrine of Elements, e.g., the deduction of the categories or the paralogisms of pure reason.” (The “paralogisms” were flawed arguments about the nature of the soul). In fact, both of these chapters would be completely rewritten in the second edition of the Critique. This was partly to respond to the Göttingen review’s challenge to his type of idealism, but also to address Kant’s own concerns about how persuasive these sections were.

Developing the Deduction of Categories

Indeed, Kant had already started showing his concern about the deduction in the Prolegomena itself. In that book, he said he was using an “analytic” method, as opposed to the “synthetic” method of the Critique.

• The “analytic” method was supposed to work by analyzing what must be true for undisputed claims of knowledge to be possible.
• The “synthetic” method was supposed to work by figuring out the consequences of fundamental claims about how human minds know things. But the main difference between Kant’s arguments in the two works was actually about which knowledge claims he analyzed.

In the Prolegomena, Kant replaced the original transcendental deduction of the categories. The original deduction tried to analyze the necessary conditions for the possibility of what he called the transcendental unity of apperception (a complex term for the unified self-consciousness that experiences the world). Instead, the Prolegomena offered an analysis of the necessary conditions for universally and necessarily valid judgments in everyday life and science. This new analysis made no use of the concept of apperception at all.

Here’s how Kant argued this:

• He said that mere “judgments of perception” only report how things seem to a single person. They don’t claim to be necessarily true for everyone or to describe objective reality. These judgments use the logical forms of judgment (like “All S is P” or “If A, then B”).
• However, “judgments of experience” do claim to be objectively valid and necessary for everyone. Kant argued that these judgments can only get their universal and necessary validity by using a priori categories. These categories make the otherwise general use of the logical forms of judgment specific and connected to experience.

Kant pushed this approach even further three years later in the Preface to his Metaphysical Foundations of Natural Science. There, he suggested that the categories could be derived as the necessary conditions for making the use of logical forms of judgment specific, even without explicitly referring to the supposed difference between judgments of perception and judgments of experience.

But this strategy has a weakness. It could be accused of “begging the question” against empiricists (who believe knowledge comes from experience) and skeptics (who doubt we can have certain knowledge). The strategy seems to prove that categories are necessary only if you already accept that ordinary and scientific knowledge-claims are universally and necessarily true. Neither a skeptic nor an empiricist would likely accept that starting point.

Return to Apperception for the Second Edition

In any case, Kant’s notes from the period 1783–1784 show that he continued to explore both the unity of apperception and the concept of objectively valid judgment as possible starting points for the deduction of the categories. However, when Kant rewrote the chapter on the transcendental deduction for the second edition of the Critique, he went back to his original strategy. He tried to combine the conditions necessary for the unity of apperception with the conditions necessary for making judgments about objects. His goal was to create an unshakeable foundation for the objective validity of the categories.

The Process of Revision for the Second Edition

In April 1786, Kant’s publisher told him that a new edition of the Critique was needed. At first, Kant apparently considered a very drastic revision. This might have included an extensive discussion of practical reason (reason related to morality and action) as well as a restatement of his work on theoretical reason (reason related to knowledge of what is). Around the same time, he also took on the job of rector (head) of his university.

At some point during that year, he must have decided on the revisions that we now have. These were still extensive, but more modest than his initial thoughts. Enough of these revisions were finished by January 1787 for the typesetting of the new edition to begin. All the revisions were apparently completed by April 1787, just a year after the new edition was first requested. (Sometime between 1781 and 1787, Kant made notes in his personal copy of the first edition of the Critique. However, these notes are not closely matched by the changes in the 1787 edition. So, there is no reason to believe these notes were made during 1786–1787 as part of the work on the new edition.)

Main Changes in the Second Edition

The main changes in the second edition grew partly out of Kant’s response to criticism of the first edition and partly out of his own concerns, as described above. Here are the key changes:

1. A New Preface:

   • Kant replaced the preface to the first edition. The original preface spoke in very general terms about the need to place the science of metaphysics on a secure footing.
   • The new preface was much longer. It described in much more detail both the innovations of Kant’s critical method and his position on the use of reason.
   • It is in this new preface that Kant introduces his famous comparison between his own procedure in philosophy and Copernicus’s revolution in astronomy. Copernicus proposed a sun-centered model of the solar system, a major shift from the earth-centered view. Kant saw his philosophy as similarly shifting the focus to the human mind’s role in shaping knowledge.
   • The new preface also emphasized Kant’s view that pure reason ultimately has a positive role only in its practical (moral) use, rather than its theoretical (knowledge-seeking) use. This emphasis was clearly meant to respond to the dismissive remarks on this subject in the Göttingen review.
   • The new preface concludes with a brief comment on the changes in the new edition, and then with a long footnote that revises even further the new “Refutation of Idealism,” which is one of the most important changes in the second edition.

2. An Expanded Introduction:

   • The introduction to the Critique was considerably expanded.
   • Its main changes were, first, a more detailed discussion of the distinction between a priori knowledge (known independently of experience) and a posteriori knowledge (known through experience) than the first edition had included.
   • Second, it included an extended argument that the a priori knowledge we have in pure mathematics and physics can only be explained by his theory of transcendental idealism. These pages were, in fact, taken almost without change from his earlier book, the Prolegomena.
   • Kant’s inclusion of these pages shows that he was still very concerned to emphasize the difference between his own idealism and Berkeley’s idealism. One of Kant’s main criticisms of Berkeley in the Prolegomena was Berkeley’s inability to explain a priori knowledge.

3. An Expanded “Transcendental Aesthetic”:

   • The “Transcendental Aesthetic” is the part of the Critique that deals with space and time as the forms of our sensibility (how we perceive things). This section was also considerably expanded.
   • Kant’s main goal in revising this section seems to have been to strengthen his argument for the necessity of his transcendental idealism to explain a priori knowledge (an anti-Berkeleian argument). This was more important here than arguing that his form of idealism is compatible with knowledge of the real existence of external objects, an issue he would address more directly in later parts of the revised work.
   • To achieve this, Kant divided his previously undivided discussions of space and time into what he now called the “Metaphysical Exposition” and the “Transcendental Exposition” of each.
     • The “Metaphysical Exposition” aimed to show that space and time are pure and a priori forms of intuition (the basic ways we perceive), and also that they are pure intuitions in their own right.
     • The “Transcendental Exposition” separately presented the argument that our a priori knowledge of mathematics (especially geometry) can only be explained by transcendental idealism.
   • The revised version of the “Aesthetic” concludes with a number of additional arguments for transcendental idealism that were not present in the first edition.

4. A Rewritten “Transcendental Deduction” of the Categories:

   • The “Transcendental Deduction” explains how the basic concepts of the understanding (the categories) can apply to objects of experience. Kant rewrote this chapter almost completely for the second edition. (Two introductory sections were left largely unchanged, but the rest was completely rewritten: thirty-five pages in the first edition were replaced with forty completely new pages in the second.)
   • It would be too complex for this introduction to describe in detail all the changes Kant made here. However, a few key points can be noted:
     • First, despite his experiments in 1783 and 1786 with a deduction that didn’t rely on apperception (self-consciousness), Kant in fact tried to ground the entire new deduction more clearly on the starting-point of the unity of apperception than he had in 1781.
     • At the same time, trying to use his experiments from the intervening years, he also tried to connect the unity of apperception more clearly with the idea of the objective validity of judgment than he had in the earlier version.
     • Second, Kant tried to prepare the way for the new “Refutation of Idealism” (which would appear later in the book). He did this by stressing that the thinking mind (the cognitive subject) must be seen as determining the structure and order of its own self-consciousness just as much as it does to the way it represents external objects.
     • Finally, Kant continued to emphasize the necessity of representing space. This was part of his response in the Prolegomena to the charge that his idealism was like Berkeley’s. He stressed that the synthetic unity of consciousness (the mind’s ability to combine information into a unified awareness), which in the first edition had been linked only with the synthesis (combination) of time, is responsible for the unity of both space and time. Indeed, he argued that representing definite spatial relationships is a necessary condition for representing a definite order in time. And a definite temporal order is an undeniable feature of any conceivable self-consciousness.

5. Revisions in the “Analytic of Principles”:

   • The “Analytic of Principles” deals with the rules the understanding uses to make judgments. The chief theme of all the revisions in this part was the argument that while time is the form of all our sensations, the representation of space is itself necessary for us to represent a definite order in time. This argument continued Kant’s rebuttal of the charge that he was a Berkeleian idealist.
   • These revisions took the form of restatements of the several principles of judgment, and of additional paragraphs at the start of each of the proofs for these principles.
   • But Kant’s most important addition to this part of the book is the new “Refutation of Idealism.” He inserted this into the discussion of actuality (what is real) in the section called the “Postulates of Empirical Thought.”
   • This might seem like an odd place for such an important addition. But Kant’s intention in choosing this location was likely to show that empirically meaningful judgments about the modalities (possibility, actuality, and necessity) all depend on being connected to what is actual in perception.
   • He then aimed to show what he meant by “the actual in perception”: that which we judge to exist independently of our representation of it. This is true even if we also know that the form in which we represent the independence of such objects is itself dependent upon the way our own minds are structured (our sensibility).
   • In other words, the “Refutation of Idealism” was Kant’s ultimate attempt to prove that his idealism is merely formal idealism (concerned with the form of knowledge) rather than the subjective idealism of Berkeley (which, according to Kant’s opponents, reduced reality to our own ideas).
   • The “Refutation of Idealism” is one of the most important of Kant’s additions to the second edition. However, the fact that before the new edition was even published he was already revising this revision in the new preface (which was presumably the last part of the book to be rewritten) shows that Kant was hardly satisfied with his new argument.
   • In fact, the new “Refutation” was not so much the final result of a long-considered process of thought. Instead, it was the beginning of a new one. A dozen or more further versions of this argument from the period 1788–1790 still exist. They show that Kant continued to work on this argument even after the second edition of the Critique had already appeared.

6. Revisions to “Phenomena and Noumena”:

   • Kant also undertook major revisions in the chapter on the distinction between phenomena (things as they appear to us through our senses and understanding) and noumena (things as they might be in themselves, independent of our minds).

His main goal in these revisions was to clearly explain the difference between using the idea of a noumenon (a thing as it is in itself, beyond our senses) in two ways:

• A negative sense: This acknowledges that there might be things beyond what our senses can experience, but we cannot know them directly. It serves as a limit to our knowledge.
• A positive sense: This is a more complex idea, related to concepts necessary for morality that reason might explore in a practical, rather than theoretical, way.

This clarification helped support another key Kantian idea: that pure reason, when used for theoretical understanding of the world, mainly shows us the limits of our knowledge (a negative use). However, when used for practical purposes, like guiding moral action, pure reason has a positive and vital role. The original Göttingen review and even Garve’s more sympathetic draft had questioned how clear this doctrine was.

7. Rewriting the “Paralogisms” (Flawed Arguments about the Soul):
   • Because Kant added his new “Refutation of Idealism” (his argument against the idea that only minds and their ideas exist), he also had to rewrite at least the fourth paralogism from the first edition. A paralogism is a piece of faulty reasoning, and in this context, Kant was addressing flawed arguments about the nature of the soul.
   • This fourth paralogism, more than any other part of the first edition, had led critics to accuse Kant of Berkeleianism – the view that physical objects are nothing more than ideas in our minds. The original argument in the first edition had stated that we could be as certain about objects outside us (outer sense) as we are about our own inner thoughts and feelings (inner sense). It suggested that objects in space were just one type of mental idea, similar to our inner thoughts.
   • Kant replaced this problematic argument with a completely different one. His new argument was anti-Cartesian, meaning it went against the views of the philosopher René Descartes. Descartes had famously struggled with how the mind and body, if they are two entirely different kinds of things, could possibly interact. Kant’s new argument suggested there shouldn’t be a deep mystery about mind-body interaction. He proposed that the apparent differences between mind (as it appears to us) and body (as it appears to us) might simply be different ways a single, underlying reality shows itself to us.
   • However, Kant didn’t just change the fourth paralogism. He took the opportunity to rewrite and simplify the entire chapter on the paralogisms.
   • Except for this major change in the fourth paralogism, this rewriting of the “Paralogisms” chapter is the only part of his revisions that really fits his claim that he was merely improving how he explained his ideas, rather than changing the substance.

Why Did the Revisions Stop There?

Beyond the chapter on the “Paralogisms of Pure Reason,” Kant did not make any other significant changes for the second edition. We don’t know for sure why he stopped.

• Was he completely satisfied with the rest of the book?
• Or did he simply run out of time and patience for more revisions?

The second explanation seems more likely. In his later major works, the Critique of Practical Reason and the Critique of Judgment, Kant continued to restate and refine many important ideas that were first introduced in the remaining parts of the Critique of Pure Reason. These include his theory of the postulates of practical reason (key assumptions needed for morality) and the regulative use of the ideas of reason (how certain guiding concepts, though not objects of knowledge themselves, help us organize and pursue knowledge). This ongoing refinement suggests he still saw areas that could be developed or clarified.

Summary of Kant’s Main Goals for the Second Edition

In summary, most of Kant’s changes in the second edition of the Critique of Pure Reason stemmed from his desire to refine and defend his system of transcendental idealism. He particularly wanted to achieve two things:

1. Show that only his transcendental idealism could properly explain how we can have a priori knowledge (knowledge that is certain and universal, like the truths of mathematics, known independently of experience).
2. Argue forcefully that his idealism was completely compatible with believing in the real existence of external objects (that is, he wasn’t saying the world outside us is just an illusion).

Beyond these central aims, Kant also wanted to:

• Emphasize the positive and essential role of reason in the practical sphere (guiding moral action), as opposed to its more limited role in theoretical knowledge of the world.
• Continue his efforts to develop a clear and convincing deduction of the categories (showing how the fundamental concepts of our understanding necessarily apply to experience).

These major concerns led Kant to substantially revise:

• His introduction to the Critique.
• The “Transcendental Aesthetic” (the section dealing with space and time as the forms of our perception).
• The chapter on the distinction between phenomena (things as they appear to us) and noumena (things as they might be in themselves).

Furthermore, these concerns caused him to completely rewrite:

• The preface to the Critique.
• The “Transcendental Deduction” of the categories (the core argument for the validity of those concepts).
• The “Paralogisms of Pure Reason” (the chapter addressing flawed arguments about the soul and self).

PREFACE1,1[A vii]

Our minds have a strange problem. We ask certain kinds of questions that we must explore. These questions come from the way our minds naturally work. But, we find ourselves unable to answer them. The answers are simply beyond what human reason can achieve.

Our minds get into this difficult situation without intending to. We start with basic ideas that we need for everyday experience. These ideas are well-supported by experience. Our minds naturally try to build on these ideas, reaching for more complex and distant explanations. But we soon realize that this process never really finishes. There are always more questions. So, our minds feel forced to rely on ideas that go beyond anything we can experience. These ideas might even seem like common sense at first.

However, this leads to confusion and contradictions. We might guess that we’ve made mistakes somewhere, but we can’t find them. This is because the ideas we are using are outside the realm of experience, so experience can’t help us check them. This constant struggle with these kinds of questions is what we call metaphysics.

Long ago, people called metaphysics “the queen of all sciences.” If good intentions counted as achievements, it would have deserved this honor. This was because the topics metaphysics deals with are incredibly important. But now, things have changed. Metaphysics is looked down upon by many. It’s like a queen who has been overthrown and abandoned, left to grieve her lost importance.

The Troubled History of Metaphysics

In its early days, metaphysics was ruled by thinkers called dogmatists. They confidently declared their ideas as absolute truths, like dictators. But their rules were often flawed, like leftover ideas from a less developed time. This led to many internal disagreements and eventually, complete chaos in the field.

Then came the skeptics. They were like wanderers who disliked any settled system of thought. They questioned everything and sometimes disrupted the dogmatists’ efforts. However, there weren’t many skeptics. So, the dogmatists kept trying to rebuild metaphysics, but they could never agree on a single, unified plan.

More recently, it seemed like these endless arguments might finally be settled. The famous philosopher John Locke proposed a theory based on how the human mind understands things. He suggested that metaphysics came from common, everyday experience. If this were true, the grand claims of metaphysics would seem questionable. However, I believe this explanation of metaphysics’ origins was wrong. So, metaphysics fell back into its old, flawed ways of asserting ideas without proper proof (dogmatism). It remained in the same state of disrespect it was supposed to be rescued from.

Now, after trying so many approaches without success, a feeling of boredom and complete indifference has taken over. This indifference is like the mother of chaos and darkness in the world of knowledge. But, at the same time, it might also be the starting point, or at least the signal, for a new beginning. It could lead to a transformation and new understanding, especially because poorly managed efforts have made metaphysics unclear, confusing, and unhelpful.

Why Indifference Isn’t the Answer

It’s pointless to pretend we don’t care about these deep questions. Human nature itself makes us care about them. Besides, even those who say they are indifferent – the “indifferentists” – often try to hide their ideas by using simple language instead of academic terms. But if they think about anything seriously, they almost always end up making metaphysical claims – the very kind of claims they said they despised.

Still, this widespread indifference is worth thinking about. It’s happening at a time when many other sciences are making great progress. And this indifference is aimed squarely at metaphysics – a field whose answers, if we could find them, would be extremely important to us.

This situation is not a sign that people today are careless thinkers. Instead, it shows that our ability to judge has matured. We are no longer satisfied with make-believe knowledge. This maturity demands that reason take on its most difficult task: to understand itself.

Reason must set up a kind of court. This court will determine what claims of reason are justified and which ones are baseless. It will do this not by making arbitrary rules, but by following reason’s own timeless and unchanging laws. This court is nothing other than the critique of pure reason itself.

The Age of Criticism

Some people complain that thinking today is superficial and that solid science is declining. But I don’t see this in sciences like mathematics and physics, which are built on strong foundations. They have kept their reputation for being well-grounded. In fact, natural science has even improved its standing. This same spirit of careful thinking could also work well in other areas of knowledge, if only we first took care to fix their basic principles.

When principles are not sound, indifference, doubt, and eventually, strict criticism are actually signs of a healthy, well-grounded way of thinking. Our time is truly an age of criticism. Everything must be open to examination. Religion, because of its sacredness, and law-making, because of its authority, often try to avoid this criticism. But by doing so, they only make themselves suspicious. They cannot earn the genuine respect that reason gives only to things that have successfully passed its free and public review.

What This “Critique” Means

When I talk about this “critique,” I don’t mean a review of specific books or philosophical systems. Instead, I mean an examination of our ability to reason in general. This critique looks at all the knowledge that reason might try to achieve without relying on any experience.

Therefore, this critique will help us decide:

• Is metaphysics as a whole even possible?
• If so, where do its ideas come from?
• What is the extent of what it can cover?
• What are its limits? All of this will be determined based on fundamental principles.

My Approach and Goals

This path of examining reason itself is the only one left, and it’s the one I have taken. I believe that by following it, I have managed to clear up all the mistakes that have caused reason to argue with itself when it tries to operate without experience.

I haven’t dodged reason’s difficult questions by simply saying “human reason can’t handle them.” Instead, I have laid out these questions clearly, based on principles. After figuring out exactly where reason misunderstood itself, I have solved these questions to reason’s complete satisfaction.

Of course, the answers I’ve found might not be what someone with a passionate, dogmatic hunger for knowledge would expect. Such a hunger could only be satisfied by some kind of magical insight, which I don’t possess. But obtaining that kind of knowledge was never the natural purpose of our reason. The job of philosophy is to get rid of illusions that arise from misunderstanding, even if this means destroying many cherished and comforting false beliefs along the way.

In this work, my main goal has been to be thorough. I dare to say that there isn’t a single problem in metaphysics that hasn’t been solved in this book, or at least for which the key to its solution hasn’t been provided. In fact, pure reason is such a perfectly unified system that if its basic principle couldn’t handle even one of the questions that reason naturally asks, then that principle would have to be thrown out. Because then, it wouldn’t be able to reliably answer any of the other questions either.

Are My Claims Too Bold?

As I say all this, I can almost see readers reacting with disapproval, perhaps even scorn, at what might seem like very bold and arrogant claims. Yet, my claims are actually far more modest than those made by any author who tries to prove things like the simple nature of the soul, or that the world must have had a first beginning.

Such authors promise to expand human knowledge far beyond all possible limits of experience. I humbly admit that doing so is completely beyond my abilities. Instead, my work deals only with reason itself and its own pure thinking. To understand these things thoroughly, I don’t need to look far beyond myself, because I find them within me. Basic logic already gives us an example of how the simple operations of reason can be fully and systematically listed. The real question here is: how much can I achieve using only these simple operations of reason, if I take away all information and help from experience?

So, that explains my goal of being complete in achieving each specific aim, and also comprehensive in achieving all of them together. These aims are not just chosen randomly. They are given to us by the very nature of knowledge itself, and they form the subject of our critical investigation.

The Importance of Certainty and Clarity

Beyond completeness, two other things are crucial for this kind of investigation: certainty and clarity. These concern the way the investigation is presented. They are essential requirements that readers have a right to expect from an author who takes on such a difficult and tricky task.

Regarding certainty, I have firmly stated that in this type of inquiry, there is absolutely no room for mere opinions. Anything that even resembles a hypothesis is like forbidden goods – it shouldn’t be offered for sale at any price but must be seized immediately if found. This is because any knowledge that claims to be certain before experience (a priori) also claims that it must be considered absolutely necessary. This is even more true for a system that defines all pure a priori knowledge. Such a system should be the very standard, and even the prime example, of all provable (philosophical) certainty.

Whether I have lived up to this promise is entirely for the reader to judge. It is an author’s job to present the arguments, not to decide how those arguments will affect the judges. However, to avoid unintentionally weakening my own points, I may be allowed to point out certain passages that could lead to some doubt. These passages might relate only to secondary goals of the work. My purpose in doing this would be to address any potential negative influence that even the slightest hesitation from the reader on these minor points might have on their judgment of the main goal of the book.

I know of no investigations more important than the ones I have carried out in the second chapter of the “Transcendental Analytic,” titled “Deduction of the Pure Concepts of the Understanding.” These inquiries are vital for truly understanding the mental ability we call the understanding. They are also key for defining the rules and limits of its use. These investigations cost me the most effort, but I hope that effort was worthwhile.

This deep inquiry has two parts:

1. One part relates to the objects of pure understanding. Its purpose is to show and explain that the understanding’s concepts, known before experience (a priori concepts), are genuinely valid when applied to objects. This part is essential to my main goals.
2. The other part deals with the pure understanding itself. It looks at how the understanding is possible and the mental powers it relies on. So, this part considers the understanding from a subjective viewpoint (related to the thinking mind itself). Although this explanation is very important for my main goal, it’s not an essential part of it.

The main question always remains: “What and how much can our understanding and reason know without any help from experience?” It’s not: “How is the ability to think itself possible?”

This second question (about how thinking is possible) is somewhat like searching for the cause of an existing effect. Therefore, it might seem like a hypothesis (though I will show elsewhere that this is not actually the case). Because of this appearance, it might look like I am just offering an opinion here, and that the reader could therefore be free to hold a different opinion.

With this in mind, I must tell the reader beforehand: even if my “subjective deduction” (the explanation of how the understanding is possible) does not completely convince you as I hope it will, the “objective deduction” (which shows the validity of the concepts) is my primary concern. This objective deduction would still be fully valid. The arguments presented earlier in this work should be enough on their own to support it.

Finally, regarding clarity, the reader has a right to expect two kinds:

1. First, logical clarity. This means the ideas are explained clearly through concepts.
2. Second, intuitive clarity. This means clarity through examples or other specific illustrations.

I have taken great care to provide logical clarity. This was essential for my project. But this also unintentionally caused me to not fully meet the second demand for examples, which is a less strict but still fair expectation.

As I worked on this book, I was almost constantly unsure how to handle this issue of examples. Examples and illustrations always seemed necessary to me. In fact, they were included in the right places in my first draft.

But then I considered the huge size of my task and the many topics I had to cover. I realized that just dealing with these topics in a dry, purely academic way would already fill a very large book. So, I decided it wasn’t wise to make it even larger by adding examples and illustrations. These are mainly needed for a popular audience. This work, however, could never really be suitable for popular reading. True experts in this science don’t need things to be made overly simple for them, even though that might be pleasant. In this case, adding too many examples could even have been unhelpful.

The Abbé Terrasson once said something interesting. If you measure a book’s length not by its number of pages but by the time it takes to understand it, then many books “would be much shorter if they were not so short.” In other words, a short, dense book can take more time to grasp than a longer one that explains things more.

But on the other hand, if we think about understanding a whole system of complex philosophical knowledge – a system that is broad yet connected by principles – we could just as rightly say that many a book “would have been much clearer if it had not been made quite so clear.” This means that things intended to help clarity in individual parts can often confuse the reader when it comes to the whole. The reader might not be able to get a quick overview of the entire system. All the “bright colors” from too many examples can paint over and hide the structure of the system. Yet, it’s this very structure that is most important when judging the system’s unity and how sound it is.

It seems to me that readers should feel quite motivated to join their efforts with mine. They have the chance to carry out a great and important piece of work, based on the outline I’ve provided. And this work can be done in a complete and lasting way.

Now, metaphysics, as I will define it here, is unique among all sciences. It’s the only one that can promise that a small but focused effort can complete it, and quickly too. After this, all that will be left for future generations is to present it in an educational way for their own purposes. They won’t be able to add anything new to its core content.

Why is this? Because metaphysics, as I see it, is simply an inventory of everything we possess through pure reason, all arranged systematically. Nothing can escape our notice here. What reason produces entirely from itself cannot stay hidden. Reason itself brings it to light as soon as reason’s common, underlying principle is discovered.

The perfect unity of this kind of knowledge makes this absolute completeness not only possible but also necessary. This knowledge comes only from pure concepts. It is not influenced by experience, nor by any specific intuition that leads to a particular experience, which might expand or change it. As an ancient writer once suggested, if you look closely at what’s inside your own mind, you’ll realize the nature and extent of your built-in “mental toolkit” before experience. Understanding this helps us map out completely what pure reason alone contains.

I hope to present such a system of pure (speculative) reason myself. It will be titled Metaphysics of Nature. That book will not be half as long as this current Critique, but it will be far richer in content. This Critique first had to lay out the sources of metaphysics and the conditions that make it possible. It needed to clear and prepare the ground, which was completely overgrown with confusion.

For this current work, the Critique, I expect the reader to have the patience and fairness of a judge. But for the future Metaphysics of Nature, I will look for the cooperative spirit and help of a fellow worker.

Here’s why: no matter how completely the principles of the system are explained in this Critique, the full scope of the system itself also requires that no secondary concepts are missing. These secondary concepts cannot all be figured out in one go before experience; they must be sought out gradually. Also, just as this Critique has fully explored the combination (synthesis) of concepts, the Metaphysics of Nature will additionally require that the same thoroughness is applied to their breakdown (analysis). This analysis will be an easy and enjoyable task, more like entertainment than hard work.

A Note on the Printing

I have only a few more comments about the printing of this book. The start of the printing was delayed a bit. As a result, I was only able to review about half of the proof pages before publication. In those pages, I found a few printing errors. However, only one of them might confuse the meaning: on one page, the word “skeptical” was printed where it should have said “specific.”

Also, the section called “The Antinomy of Pure Reason” is arranged like a table. Everything related to the main argument (the thesis) is on the left side. Everything related to the counter-argument (the antithesis) is on the right side. I did this to make it easier for readers to compare each proposition with its opposing counter-proposition.

Preface to the second edition

We can usually tell if a field of study is on the right track to becoming a true science by looking at its success.

• Does it get stuck right when it’s about to reach its goal, even after a lot of groundwork?
• Does it have to keep going back to the beginning and try a new path?
• Can the different people working in that field not agree on how to achieve their common aim? If these things are happening, we can be sure the field is just stumbling around. It is far from being a secure science. It’s actually a service to human reason if we can find the correct path for such a study, even if we have to give up many ideas that were part of its earlier, poorly thought-out goals.

Logic: A Secure But Limited Science

We can see that logic has been on a secure path since ancient times. Since the time of Aristotle, it hasn’t really needed to take any steps backward. The only changes have been minor things, like removing some unnecessary details or making its explanations clearer. These are more about making logic look elegant than about changing its core security. What’s also remarkable about logic is that it hasn’t been able to take any significant steps forward either. For all intents and purposes, it seems finished and complete.

Some modern thinkers have tried to expand logic. They’ve added chapters from:

• Psychology: about our different mental abilities like imagination or wit.
• Metaphysics: about where knowledge comes from, or the different kinds of certainty depending on the subject (like idealism or skepticism).
• Anthropology: about our prejudices, their causes, and how to fix them. But these attempts come from not understanding the special nature of logic.

Allowing the boundaries of sciences to blur into one another doesn’t improve them; it deforms them. The boundaries of logic, however, are very clear. Logic is the science that fully lays out and strictly proves only the formal rules of all thinking. It doesn’t matter if this thinking is based on experience or known before experience (a priori). It doesn’t matter what its origin or subject is, or what accidental or natural obstacles it faces in our minds.

Logic’s success and advantage come from its very limitation. It is allowed – and indeed, required – to ignore all actual objects of knowledge and the differences between them. In logic, therefore, the understanding deals only with itself and its own structure.

The Challenge for Other Sciences

Naturally, it must be much harder for reason to find the secure path of a science when it has to deal with objects, not just with itself. So, logic acts like a basic introduction, an outer courtyard, to the other sciences. When we want to gain actual information, we might use logic to judge it. But we must seek the information itself in the sciences that deal directly with objects.

If these other sciences are to involve reason, then something in them must be known a priori (before or without experience). This a priori knowledge can relate to its object in two ways:

1. Theoretical knowledge: This simply defines the object and its concept (which must come from somewhere else).
2. Practical knowledge: This also makes the object real or brings it into existence.

In both theoretical and practical knowledge, the pure part – where reason defines its object entirely a priori – must be explained on its own. It doesn’t matter how much or how little this pure part contains. It must not be mixed with what comes from other sources. It’s like bad financial management to spend all your income blindly. Later, when things get tight, you won’t be able to tell which part of your income can cover expenses and which part needs to be cut.

Mathematics and physics are two theoretical sciences that aim to define their objects a priori. Mathematics does this in a completely pure way. Physics does it at least partly in a pure way, but it also follows standards from sources of knowledge other than pure reason.

Science Revolutions: Mathematics

Mathematics has traveled the secure path of a science from the earliest times of human history, starting with the ancient Greeks. Yet, we shouldn’t think it was as easy for mathematics as it was for logic (where reason only deals with itself). Mathematics didn’t just find this “royal road”; it had to create it. I believe mathematics involved a lot of trial and error for a long time, especially among the Egyptians. Its transformation into a secure science was due to a revolution. This revolution was sparked by the brilliant idea of a single person. From that attempt onward, the correct path could no longer be missed. The secure course of a science was established and set for all time, with infinite possibilities for extension.

The history of this revolution in thinking – which was far more important than discovering the sea route around Africa – and the name of the lucky person who brought it about, haven’t been preserved. But a story passed down by Diogenes Laertius (who names the supposed inventor of even the simplest elements of geometric proofs, things most people think don’t need proof) shows something important. It proves that the memory of the change brought by this new path, even in its earliest stages, must have seemed extremely important to mathematicians. That’s why it was never forgotten.

A new light dawned upon the first person (whether he was called Thales or something else) who demonstrated a property of a shape, like the isosceles triangle. He found that he didn’t have to just look at the figure, or even analyze its concept, to understand its properties. Instead, he had to produce the properties from what he himself thought into the object and presented (through construction) according to a priori concepts. He realized that to know something securely a priori, he had to attribute to the thing nothing except what necessarily followed from what he himself had put into it according to its concept.

Science Revolutions: Natural Science (Physics)

Natural science (physics) took much longer to find the main road of science. It was only about a century and a half ago that the suggestions of the brilliant Francis Bacon partly caused this discovery and partly encouraged it further, as people were already close to finding it. This discovery, therefore, can also be explained by a sudden revolution in the way of thinking. Here, I will only consider natural science as it is based on principles from experience.

When scientists like Galileo rolled balls of a chosen weight down a sloped surface, or when Torricelli made air support a weight he had figured was equal to a known column of water, or when later, Stahl turned metals into powders (calx) and then back into metal by removing something and then putting it back – a light dawned on all students of nature. They understood that reason only has insight into what it itself produces according to its own plan. Reason must take the lead. It must use its principles for judgments, according to constant laws. It must compel nature to answer its questions. Reason cannot just let nature lead it around, like a child on a leash. If it does, accidental observations, made without any prior plan, can never be connected into a necessary law. Yet, such necessary laws are precisely what reason seeks and requires.

Reason must approach nature to be taught by it. But it must do so with two things:

1. In one hand, its principles, according to which alone consistent observations can count as laws.
2. In the other hand, experiments designed according to these principles. Reason acts not like a student who just repeats whatever the teacher says. Instead, it acts like an appointed judge who forces witnesses to answer the questions put to them. So, even physics owes its beneficial revolution in thinking to this insight: reason has to seek in nature what it itself puts into nature, based on what reason would not be able to know on its own and has to learn from nature. This is how natural science was finally set on the secure path of a science, after so many centuries of just groping in the dark.

Metaphysics: Still Searching for Its Path

Metaphysics is a completely isolated, speculative type of knowledge from reason. It raises itself entirely above anything that experience can teach. It works only through concepts (not, like mathematics, by applying concepts to our perceptions or intuitions). In metaphysics, reason is supposed to be its own student. So far, metaphysics has not been lucky enough to enter the secure path of a science. This is true even though it is older than all other sciences and would likely remain even if all other sciences were destroyed by some overwhelming barbarism. In metaphysics, reason continually gets stuck. This happens even when it claims to have a priori insight (as it pretends to) into laws that are confirmed by the most common experiences. In metaphysics, we have to go back and retrace our path countless times because we find it doesn’t lead where we want to go. Metaphysics is so far from achieving agreement among its followers that it’s more like a battlefield. This battlefield seems specially designed for people to test their powers in pretend fights. On this field, no fighter has ever gained the smallest piece of ground. No one has ever been able to build any lasting claim based on a victory. Therefore, there is no doubt that up to now, the method of metaphysics has been mere groping. And worst of all, it has been a groping just among concepts.

Why Has Metaphysics Failed So Far?

Now, why is it that the secure path of science still hasn’t been found in metaphysics? Is it perhaps impossible? If so, why has nature burdened our reason with a restless striving for such a path, as if finding it were one of reason’s most important tasks? Even more, how little reason do we have to trust our own reason if, in one of the most important areas of our desire for knowledge, it not only abandons us but even tricks us with illusions and, in the end, betrays us! Or, if the path has merely been missed so far, what signs can we look for that might give us hope that in new attempts, we will be luckier than those who came before us?

A New Approach for Metaphysics: The “Copernican Revolution”

I believe the examples of mathematics and natural science are remarkable enough. They became what they are now through a sudden revolution in their way of thinking. We should reflect on the key element in this advantageous change. We should, at least as an experiment, try to imitate it in metaphysics, as much as the similarity between metaphysics and these other rational forms of knowledge allows.

Up to now, people have assumed that all our knowledge must match up with objects. But based on this assumption, all attempts to find out something about objects a priori (before experience) through concepts, in a way that would expand our knowledge, have failed. So, let us try something different. Let’s assume that objects must match up with our knowledge. This idea might fit better with the possibility of having a priori knowledge of objects – that is, knowledge that tells us something about objects before they are actually given to us.

This is like the first thoughts of Copernicus. He wasn’t making good progress in explaining the movements of the planets by assuming that all the stars and planets revolved around the observer (Earth). So, he tried to see if he might have better success if he made the observer (Earth) revolve and left the stars at rest.

We can try a similar approach in metaphysics regarding our intuition (our direct perception or sensing) of objects.

• If our intuition has to match the nature of the objects themselves, then I don’t see how we can know anything about them a priori.
• But, if the object (as an object of our senses) matches the nature of our faculty of intuition (our way of perceiving), then I can very well imagine this possibility.

How the New Approach Works

However, I cannot stop with just these intuitions if they are to become actual knowledge. I must relate them, as mental representations, to something as their object and define that object through them. Here, I can assume one of two things:

1. The concepts through which I define the object also match the objects themselves. If so, I’m back in the same difficulty: how could I know anything about them a priori?
2. Or, I can assume that the objects – or what amounts to the same thing, the experience in which alone they can be known (as given objects) – match those concepts. In this case, I immediately see an easier way out of the difficulty. Experience itself is a kind of knowledge that requires the understanding. I must presuppose the rule of this understanding in myself before any object is given to me – therefore, a priori. This rule is expressed in a priori concepts. All objects of experience must therefore necessarily match these concepts and agree with them.

As for objects that are thought merely through reason, and thought of as necessary, but that cannot be given in experience at all (at least not as reason thinks them) – the attempt to think about them (for they must be thinkable) will provide an excellent test of our new proposed method. This method suggests that we can know a priori about things only what we ourselves have put into them.

Success and a Surprising Outcome

This experiment works as well as we could wish. It promises to set metaphysics on the secure course of a science, at least in its first part. This first part deals with a priori concepts to which corresponding objects can be given in experience. After this change in our way of thinking, we can very well explain the possibility of a priori knowledge. What’s more, we can provide satisfactory proofs of the laws that are the a priori foundation of nature (nature understood as the sum total of all objects of experience). Both of these things were impossible according to the earlier way of thinking.

But from this explanation of our ability to know things a priori (in the first part of metaphysics), a very strange result emerges. This result appears very unhelpful for the main goal of the second part of metaphysics. The result is that with this faculty of a priori knowing, we can never get beyond the boundaries of possible experience. Yet, going beyond experience is precisely the most essential task of metaphysics.

The Meaning of This Limitation: Appearances and Things in Themselves

However, this very limitation provides a way to check the truth of our first assessment of our a priori rational knowledge. This assessment is that such knowledge only reaches appearances (things as they appear to us). It leaves the thing in itself (the thing as it is independently of our perception) as something real in itself but not known by us.

What necessarily drives us to try to go beyond the boundaries of experience and all appearances is the unconditioned. Reason necessarily and rightly demands the unconditioned in things in themselves for everything that is conditioned (dependent on other things). In doing so, reason demands the complete series of conditions.

Now, let’s consider two assumptions:

1. If we assume that our knowledge from experience matches objects as things in themselves, then the unconditioned cannot be thought at all without contradiction.
2. However, if we assume that our representation of things as they are given to us does not match these things as they are in themselves, but rather that these objects as appearances match our way of representing them, then the contradiction disappears.

Therefore, the unconditioned must not be found in things as far as we are acquainted with them (as they are given to us). Instead, it must be found in things as far as we are not acquainted with them – as things in themselves. This would show that what we initially assumed only as an experiment (that objects conform to our cognition) is well-grounded.

The Role of Practical Reason

Now, after speculative reason (reason used for theoretical knowledge) has been denied all progress in this field beyond the senses, what remains for us is to try something else. We need to see if there isn’t information in reason’s practical data (data related to moral action and duty) that can help us define that transcendent rational concept of the unconditioned. This might allow us to reach beyond the boundaries of all possible experience, in line with the wishes of metaphysics. It might make a priori knowledge possible, but only from a practical standpoint.

By using these methods, theoretical reason has at least created space for such an expansion of our understanding, even if it had to leave that space empty for now. We are free – indeed, reason itself calls on us – to try to fill this space, if we can, using information from practical reason (reason related to moral action).

The Goal of This Critique: A Revolution in Method

The main purpose of this critique of pure theoretical reason is to try to change the usual way metaphysics is done. It aims to start a complete revolution, following the example of geometers and natural scientists. This book is a guide to the method of metaphysics, not a complete system of the science itself. However, it does map out the entire plan for the science of metaphysics. This includes its boundaries and its whole internal structure.

Pure theoretical reason has a special quality:

• It can and should measure its own abilities according to the different ways it chooses the objects of its thought.
• It can also fully list the many ways it sets up problems for itself. In this way, it can map out the entire preliminary sketch of a complete system of metaphysics.

This is possible for two reasons:

1. Regarding knowledge we have before experience (a priori knowledge), nothing can be said about objects except what the thinking mind itself contributes.
2. Regarding principles of knowledge, pure theoretical reason is a completely separate and self-contained system. Like an organized body, every part exists for the sake of all the other parts, and all other parts exist for its sake. No principle can be accepted with certainty in one area unless its connection to the entire use of pure reason has been thoroughly examined.

The Unique Potential of Metaphysics

Because of this, metaphysics also has a rare piece of good fortune. No other science based on reason that deals with objects has this (logic, for instance, only deals with the general form of thinking). If this critique successfully sets metaphysics on the secure path of a science, then metaphysics can fully cover its entire field of knowledge. It can then complete its work and leave it for future generations as a foundational structure that can never be expanded. This is because metaphysics deals only with principles and the limits on their use – limits that are determined by the principles themselves. Therefore, as a fundamental science, metaphysics is also required to achieve this completeness. We must be able to say of it, as the old saying goes: “consider nothing done if anything remains to be done,” emphasizing the need for absolute thoroughness.

The True Value of This Critical Work

But, people will ask: What kind of treasure are we planning to leave for the future with a metaphysics that has been purified by criticism, and by that process, made unchanging?

Initial Negative Use: Limiting Speculative Reason Looking quickly at this work, one might think its only use is negative. It seems to teach us never to try to go beyond the boundaries of experience with theoretical reason. And indeed, that is its first useful purpose.

Positive Use: Protecting Practical Reason But this usefulness soon becomes positive. We realize that the principles that theoretical reason uses when it tries to go beyond its boundaries don’t actually extend our use of reason. Instead, if you look at them closely, they inevitably narrow it. They do this by threatening to stretch the boundaries of sense-experience (where these principles truly belong) over everything. This can even push aside the use of pure practical reason (reason related to morality).

So, a critique that limits the theoretical use of reason is, in that respect, certainly negative. But, because it also removes an obstacle that limits or even threatens to destroy the practical use of reason, this critique is actually of positive and very important use. This becomes clear as soon as we convince ourselves that there is an absolutely necessary practical use of pure reason – the moral use. In this moral use, reason unavoidably extends itself beyond the limits of sense-experience. It doesn’t need any help from theoretical reason for this, but it must be protected from any interference from theoretical reason, so it doesn’t end up contradicting itself.

To deny that this service of criticism has any positive value would be like saying that the police have no positive value because their main job is just to stop the violence that people might fear from others. By stopping violence, the police allow everyone to go about their business in peace and safety, which is a positive outcome.

Key Discoveries of the Critique

Our Knowledge Is Limited to Appearances In the analytical part of this critique, it is proven that:

• Space and time are only forms of our sensory perception, and therefore only conditions for the existence of things as appearances.
• We have no concepts in our understanding, and thus no elements for knowing things, unless a perception corresponding to these concepts can be given.
• Consequently, we cannot know any object as a thing in itself (as it is independently of our perception). We can only know it as an object of sensory perception, that is, as an appearance. From this, it follows that all possible theoretical knowledge of reason is limited to mere objects of experience.

Thinking Beyond Appearances: Things in Themselves Yet, we must also carefully note this reservation: even if we cannot know these same objects as things in themselves, we must at least be able to think of them as things in themselves. Otherwise, the absurd idea would follow that there can be an appearance without anything that actually appears.

Resolving the Conflict Between Freedom and Natural Necessity Now, imagine if we didn’t make the distinction that our critique has shown to be necessary – the distinction between things as objects of experience (appearances) and the very same things as things in themselves. If we didn’t make this distinction, then the principle of causality (cause and effect), and therefore the mechanism of nature in determining causes, would apply to all things generally as active causes. In that case, I couldn’t say of the same thing (for example, the human soul) that its will is free and, at the same time, that it is subject to natural necessity (meaning it is not free), without falling into an obvious contradiction. This is because in both statements, I would have understood the soul in exactly the same way – namely, as a thing in general (as a thing in itself). Without prior critique, I could not have understood it otherwise.

But, if the critique is not mistaken in teaching that an object should be understood in a twofold way – namely, as an appearance or as a thing in itself; and if its explanation of the pure concepts of the understanding is correct, meaning the principle of causality applies only to things in the first sense (as objects of experience), while things in the second sense (as things in themselves) are not subject to it; then the following is possible: The very same will can be thought of in its appearance (in visible actions) as necessarily subject to the law of nature, and in this respect, not free. Yet, on the other hand, the same will can be thought of as belonging to a thing in itself, as not subject to that law of nature, and therefore free. This can be thought without any contradiction.

The Importance for Morality Now, although I cannot know my soul (when considered as a thing in itself) through any theoretical reason (and certainly not through empirical observation), and therefore I cannot know freedom as a property of any being to which I attribute effects in the world of sense (because then I would have to know such a being as determined by cause and effect in time, which is impossible since I have no perception to support such a concept of the soul), I can nevertheless think freedom to myself. That is, the idea of freedom at least contains no contradiction in itself, as long as our critical distinction between the two ways of representing things (sensory and intellectual) remains, along with the resulting limitation of the pure concepts of the understanding and the principles that flow from them.

Now, suppose that morality necessarily presupposes freedom (in the strictest sense) as a property of our will. Suppose morality cites, as evidence for this freedom, certain original practical principles that lie in our reason – principles that would be absolutely impossible without presupposing freedom. Yet, suppose theoretical reason had proven that freedom cannot be thought at all. In that case, the moral presupposition of freedom would have to give way to the theoretical claim (whose opposite, the denial of freedom, would seem to contain a clear contradiction with the proof). Consequently, freedom, and with it morality (for morality would not be contradictory if freedom were not already presupposed), would have to yield to the mechanism of nature.

But, since for morality I need nothing more than for freedom not to contradict itself, for it to be at least thinkable that it doesn’t block the mechanism of nature in the same action (when that action is considered in a different relation), without needing any further insight into freedom: the doctrine of morality can assert its place, and the doctrine of nature can assert its own. This, however, would not have been possible if this critique had not first taught us about our unavoidable ignorance regarding things in themselves and limited everything we can know theoretically to mere appearances.

The same kind of explanation of the positive usefulness of the critical principles of pure reason can be given for the concepts of God and of the simple nature of our soul. However, I will skip this for the sake of brevity.

Denying Knowledge to Make Room for Faith Thus, I cannot even assume God, freedom, and immortality for the sake of the necessary practical use of my reason unless I simultaneously deprive theoretical reason of its claims to extravagant insights. This is because, to achieve such insights, theoretical reason would have to use principles that actually only reach objects of possible experience. If these principles were applied to what cannot be an object of experience, they would always transform it into an appearance, and thus declare any practical extension of pure reason to be impossible. Therefore, I had to deny knowledge in order to make room for faith. The dogmatism of metaphysics – that is, the prejudice that reason can make progress in metaphysics without criticism – is the true source of all unbelief that conflicts with morality. This kind of unbelief is always very dogmatic itself.

Benefits of a Critically Grounded Metaphysics So, even if it may not be all that difficult to leave future generations the legacy of a systematic metaphysics, built according to the critique of pure reason, this is still a gift deserving of no small respect. To see this, we only need to:

• Compare the culture of reason that is set on the secure path of a science with reason’s unfounded groping and aimless wandering about without critique.
• Consider how much better young people hungry for knowledge might spend their time than in the usual dogmatism. This dogmatism so early and so much encourages them to quibble complacently about things they do not understand, and things into which neither they nor anyone else in the world will ever have any insight. It even encourages them to start inventing new thoughts and opinions, and thus to neglect learning the well-grounded sciences. But we see the value of critique above all when we consider how it puts an end, for all future time, to objections against morality and religion in a Socratic way – namely, by the clearest proof of the ignorance of those who make the objections.

For there has always been some kind of metaphysics to be found in the world, and there will always continue to be one. And with it, there will always be a dialectic of pure reason (reason’s natural tendency to create illusions and contradictions when it misapplies its concepts). Therefore, it is the first and most important task of philosophy to deprive this dialectic, once and for all, of all its harmful influence by blocking off the source of the errors.

No Real Loss to Humanity

With this important change in the field of the sciences, and with the loss of its previously imagined possessions that theoretical reason must accept, everything still remains in the same advantageous state as before regarding universal human concerns and the usefulness that the world has so far drawn from the teachings of pure reason. The loss only affects the monopoly of the academic schools and in no way the genuine interests of human beings. I ask the most inflexible dogmatist:

• Has the proof of the continuation of our soul after death (drawn from the idea of the soul as a simple substance)…
• Or the proof of the freedom of the will against universal mechanism (drawn from subtle though powerless distinctions between different kinds of practical necessity)…
• Or the proof of the existence of God (drawn from the concept of a most real being, or from the contingency of changeable things and the necessity of a first mover)… …have any of these proofs, after starting in the academic schools, ever been able to reach the public or have the slightest influence on its convictions?

If those complicated academic proofs have never truly reached the public, and if we can’t expect them to (because the common human understanding isn’t suited for such subtle thinking), then people’s strong beliefs, when they are based on rational grounds, must have come about in other ways:

• Regarding the hope for a future life: This comes from a remarkable tendency in our nature, which everyone notices. We are never fully satisfied by temporary things, because such things are always insufficient for the deeper purposes of our lives.
• Regarding the consciousness of freedom: This comes from a clear understanding of our duties, which often oppose our desires.
• Regarding faith in a wise and great creator: This comes from the wonderful order, beauty, and care evident everywhere in nature.

So, these widely held beliefs not only remain undisturbed by our critical work, but they even gain more respect. This is because the academic schools are now instructed not to claim any higher or deeper insight on these universal human concerns than what is available to the general public (who always deserve our highest respect). The schools should limit themselves to developing only those reasons for proof that everyone can grasp and that are sufficient from a moral viewpoint.

The change, therefore, only affects the arrogant claims of these schools. They like to present themselves as the sole experts and guardians of such truths (as they rightly can be in many other areas of knowledge). They might share the use of such truths with the public, but they try to keep the key to understanding them for themselves.

The Role of Philosophers and the Critique

However, care is also taken to ensure a more fair role for the speculative philosopher (the philosopher who deals with theoretical reason). This philosopher remains the exclusive guardian of a science that is useful to the public even if the public doesn’t know about it. This science is the critique of reason. This critique can never become popular, and it doesn’t need to be. Most people don’t want to fill their heads with very detailed arguments for useful truths. Likewise, equally detailed objections against these truths rarely enter their minds. But, because academic thinkers (and anyone who delves into deep speculation) inevitably encounter both these detailed arguments and objections, the critique of reason is essential. By thoroughly investigating the rights of theoretical reason, it aims to prevent, once and for all, the scandal that eventually arises in public disputes. These are disputes that metaphysicians (and sometimes even clergy) get into when there’s no criticism, and in which they later even distort their own teachings.

Only through criticism can we cut away the very roots of:

• Materialism (the idea that only matter exists)
• Fatalism (the idea that events are predetermined)
• Atheism
• Free-thinking unbelief
• Enthusiasm (excessive, unreasoned religious fervor) and superstition (which can harm society generally)
• And finally, idealism (the idea that reality is fundamentally mental) and skepticism (the idea that certain knowledge is impossible), which are more dangerous to the academic schools and hardly spread to the public.

If governments think it’s good to be involved in the affairs of scholars, it would better suit their wisdom and concern for both science and humanity if they supported the freedom of such a critique. Only through this critique can the discussions of reason be placed on a firm footing. This is much better than supporting the ridiculous dictatorship of the schools, which loudly cry “public danger!” whenever someone tears apart their intellectual cobwebs – cobwebs that the public has never noticed and whose loss it would never feel.

Guiding Principles for a Reformed Metaphysics

Criticism vs. Dogmatism in Science Criticism is not opposed to the dogmatic procedure of reason when reason is used in its pure knowledge as a science. Science must always be dogmatic; that is, it must prove its conclusions strictly, based on secure principles known before experience (a priori principles). Instead, criticism is opposed only to dogmatism. Dogmatism is the arrogant assumption that one can get along just fine with pure knowledge derived from (philosophical) concepts according to principles that reason has used for a long time, without first asking how and by what right reason obtained them. Dogmatism, therefore, is the dogmatic procedure of pure reason without a prior critique of its own ability.

This opposition to dogmatism should not be seen as supporting superficial chattering that pretends to be popular thinking, or even skepticism that quickly dismisses all metaphysics. Rather, criticism is the necessary preparatory work for advancing metaphysics as a well-grounded science. This science must be dogmatic, carried out systematically according to the strictest requirements – meaning, with academic rigor, not in a popular style. It cannot neglect this requirement because it aims to conduct its business entirely a priori and thus to the complete satisfaction of theoretical reason.

Learning from Past Methods, Adding Critique In someday carrying out the plan that this critique lays out – that is, in the future system of metaphysics – we will have to follow the strict method of the famous Wolff. He was the greatest among all dogmatic philosophers and gave us the first example of how to pursue the secure path of a science. (His example created a spirit of well-grounded thinking in Germany that still exists.) This method involves:

• Regularly identifying the principles.
• Clearly defining the concepts.
• Attempting to be strict in proofs.
• Preventing bold leaps in reasoning.

For these reasons, Wolff had the skills to bring a science like metaphysics to this secure state. If only it had occurred to him to prepare the ground for it by a critique of the tool itself, namely, pure reason! This oversight is not so much his fault as it is the fault of the dogmatic way of thinking common in his era. For this, the philosophers of his time, and of all previous times, have nothing to blame themselves for. Those who reject Wolff’s kind of teaching and, at the same time, reject the procedure of the critique of pure reason can only have one goal in mind: to throw off the chains of science altogether. They want to transform serious work into mere play, certainty into opinion, and philosophy into philodoxy (the mere love of holding opinions, rather than the love of wisdom).

Changes Made in This Second Edition

Core Ideas Remain Unchanged Regarding this second edition, I wanted, as is proper, to use the opportunity to remove, as much as possible, those difficulties and unclear points that may have caused several misunderstandings. Intelligent people fell into these misunderstandings when judging this book, perhaps partly due to my own fault. I have found nothing to change in:

• The main propositions themselves.
• Their grounds of proof.
• The form and completeness of the book’s plan.

This is partly due to the long period of careful examination I subjected them to before publishing. It’s also partly due to the nature of the subject itself – that is, the nature of a pure theoretical reason. Pure reason contains a truly interconnected structure of parts, where each part is an organ. This means everything exists for the sake of each part, and each individual part exists for the sake of all the others. As a result, even the smallest weakness, whether it’s a mistake or something missing, must inevitably show itself when the system is used. I hope this system will continue to stand in this unchangeable form. It’s not self-praise that gives me this confidence. Rather, it’s the evidence from the experiment: the result is the same whether we start from the smallest elements and build up to the whole of pure reason, or if we return from the whole (which is also given through the final aim of pure reason in practical matters) to every part. Attempting to change even the smallest part directly introduces contradictions, not just into the system, but into universal human reason.

Improvements in Presentation However, in the way the material is presented, there is still much to do. This is where I have tried to make improvements in this edition. These improvements should remove:

1. Misunderstanding of the “Aesthetic” (the part about sensibility), especially regarding the concept of time.
2. Lack of clarity in the “Deduction of the Concepts of the Understanding.”
3. The supposed lack of sufficient evidence in the proofs of the “Principles of Pure Understanding.”
4. Finally, the misinterpretation of the “Paralogisms” (flawed arguments) made against rational psychology.

My revisions to the style of presentation extend only to this point (that is, only to the end of the first chapter of the “Transcendental Dialectic”) and no further. This was because time was too short. Also, regarding the rest of the book, no misunderstandings were brought to my attention by expert and impartial examiners (whom I haven’t been able to name with the praise they deserve). However, they will see in the relevant passages that I have paid attention to their reminders.

A Small Trade-off for Clarity This improvement, however, comes with a small loss for the reader. This loss could not be avoided without making the book too large. Specifically, various things that are not absolutely essential for the completeness of the whole book had to be left out or shortened. Some readers may not like doing without them, as they could still be useful in other ways. Only by doing this could I make room for what I hope is a more understandable presentation. This new presentation fundamentally changes absolutely nothing regarding the propositions or even their grounds of proof. However, it departs so far from the previous edition in its method of presentation that the changes could not have been managed simply by inserting new material. This small loss, which anyone can make up for by comparing the first and second editions if they wish, is, I hope, more than compensated for by greater clarity.

Hope for the Future of the Critique

Trust in Other Scholars In various public writings (partly in reviews of some books, partly in special articles), I have noticed with gratitude and enjoyment that the spirit of well-grounded thinking has not died out in Germany. It has only been temporarily drowned out by the fashionable noise of a so-called freedom of thought that fancies itself clever. I see that the difficult paths of criticism – leading to a science of pure reason that is academically rigorous but, as such, the only lasting and therefore most necessary science – have not stopped courageous and clear minds from mastering them. To these deserving individuals, who so fortunately combine deep insight with a talent for clear presentation (something I am aware I do not have myself), I leave the task of completing my work, which may be lacking in clarity here and there.

Kant’s Own Future Work In this case, the danger is not that I will be refuted, but that I will not be understood. For my own part, from now on I cannot get involved in controversies. However, I will pay careful attention to all suggestions, whether they come from friends or opponents, so that I may use them, in line with this introductory work, in the future development of the system. Since I have become rather advanced in age during these labors (this month I will reach my sixty-fourth year), I must use my time carefully if I am to carry out my plan of providing both the metaphysics of nature and the metaphysics of morals. These works will serve as confirmation of the correctness of the critique of both theoretical and practical reason. I must rely on those deserving individuals who have made this critique their own to shed light on those unclear points that are hard to avoid at the beginning of such a work, as well as to defend the whole.

On Understanding New and Complex Systems

Any philosophical work may face criticism on particular passages, as it cannot be as perfectly protected as a mathematical treatise. However, the whole structure of the system, considered as a unified whole, can proceed without the slightest danger. When a system is new, few people have the mental skill to get an overview of it. And because all innovation is an inconvenience to them, even fewer have the desire to try. Also, in any piece of writing, apparent contradictions can be found if individual passages are torn out of context and compared with each other. This is especially true in a work of informal discussion. In the eyes of those who rely on the judgment of others, such out-of-context comparisons can cast a negative light on the writing. However, these apparent contradictions can be very easily resolved by someone who has mastered the idea of the whole. Meanwhile, if a theory is truly durable, then in time, the criticisms and reactions that at first seemed to threaten it greatly will only serve to polish away its rough spots. If people of impartiality, insight, and true ability to communicate make it their business to do this, then in a short time they will produce even the required elegance.

Introduction

I. The Idea of a Special Kind of Philosophy (Transcendental Philosophy)

Where Our Knowledge Begins Experience is undoubtedly the first thing our understanding produces. It does this by working on the raw material of what our senses tell us. For this very reason, experience is our first teacher. As we go through life, experience offers so much new information that future generations will always continue to learn new things from it. However, experience is far from the only area our understanding is limited to. Experience tells us what is, but it never tells us that things must be a certain way and not otherwise. Because of this, experience doesn’t give us true, universal knowledge. Our reason strongly desires this kind of universal knowledge, so experience stimulates reason more than it satisfies it.

Knowledge Beyond Experience (A Priori Knowledge) Such universal knowledge, which also has the character of being internally necessary, must be clear and certain on its own, without relying on experience. This is why we call such knowledge a priori knowledge (knowledge known before or independently of experience). In contrast, knowledge that is simply borrowed from experience is called a posteriori knowledge, or empirical knowledge (knowledge known after or through experience).

Hidden A Priori Elements in Experience What’s especially remarkable is that even within our everyday experiences, there are elements of knowledge that must have come from a priori sources. These elements perhaps help us connect the various pieces of information our senses give us. If we mentally remove from our experiences everything that comes from our senses, some original concepts and judgments based on them still remain. These concepts and judgments must have arisen entirely a priori, independently of experience. This is because they allow us to say more about the objects we sense than mere experience could teach us. Or, at least, they make us believe we can say more. They allow us to make statements that have true universality and strict necessity – qualities that purely empirical knowledge can never provide.

Knowledge That Leaves Experience Behind But there’s something even more significant. Certain kinds of knowledge even leave the field of all possible experiences. They seem to expand what we can judge beyond all limits of experience. They do this through concepts for which no corresponding object can ever be found in experience.

It is precisely in these latter kinds of knowledge – those that go beyond the world of the senses, where experience can offer no guidance or correction – that we find the investigations of our reason. We believe these investigations are far more important and have a much higher ultimate goal than anything our understanding can learn from the world of appearances. We would rather risk everything, even the chance of being wrong, than give up such important investigations due to any doubts, or out of contempt and indifference.

Why We Haven’t Questioned A Priori Knowledge Sooner Now, it might seem natural that as soon as we venture beyond experience, we wouldn’t immediately start building theories with knowledge whose source we don’t know. It seems natural we wouldn’t rely on principles whose origins are unknown, without first carefully checking if our foundation is secure. So, one might think we would have long ago asked:

• How does our understanding arrive at all this a priori knowledge?
• What is its scope, its validity, and its value?

And indeed, this would be the natural course of action, if by “natural” we mean what properly and reasonably ought to happen. But if by “natural” we mean what usually happens, then, conversely, nothing is more natural and understandable than the fact that this investigation has been neglected for so long.

Reasons for This Neglect There are several reasons for this neglect:

1. One part of this a priori knowledge, namely mathematics, has been reliable for a very long time. This creates a favorable expectation for other kinds of a priori knowledge, even if they are of a completely different nature.
2. Furthermore, once you are beyond the circle of experience, you are safe from being contradicted by experience.
3. The thrill of expanding one’s knowledge is so great that progress is usually only stopped by encountering a clear contradiction. However, one can often avoid such contradictions by making one’s claims carefully, even if those claims are still just inventions.

Mathematics gives us a brilliant example of how far we can go with a priori knowledge, independently of experience. It’s true that mathematics deals with objects and knowledge only insofar as these can be shown in an intuition (a direct, immediate representation, like seeing a shape or imagining one). However, this point is easily overlooked because the intuition in question can itself be given a priori (e.g., we can imagine a triangle without needing to see a physical one). Thus, it can hardly be distinguished from a mere pure concept. Encouraged by such proof of the power of reason, our drive to expand our knowledge sees no limits.

The Dove and Plato: A Lesson in Limits Imagine a light dove, flying freely and cutting through the air. It feels the air’s resistance. It might get the idea that it could fly even better in a space with no air at all. Similarly, the philosopher Plato left the world of the senses because it presented so many difficulties for the understanding. He dared to go beyond it on the “wings of ideas,” into the empty space of pure understanding. He didn’t notice that he made no progress with his efforts. He had no resistance, no support, so to speak, against which he could push and use his powers to get his understanding to achieve anything.

Building First, Checking Foundations Later It is a common fate of human reason in its speculations to finish building its theories as quickly as possible. Only then does it investigate whether the ground for these theories was adequately prepared. At that point, all sorts of excuses are sought to reassure us of the theory’s sturdiness, or to refuse such a late and dangerous examination. What keeps us free from worry and suspicion during the construction, and flatters us with a false sense of thoroughness, is this: A large part, perhaps the largest part, of our reason’s business consists in analyzing the concepts we already have of objects. This gives us a lot of knowledge. This knowledge, however, is nothing more than illumination or clarification of what is already thought in our concepts (though perhaps in a confused way). At least in its form, this knowledge is treasured as if it were new insight. But it doesn’t actually extend the concepts we have in terms of their matter or content; it only separates them from each other or makes them clearer. Now, since this analytical procedure does yield real a priori knowledge that makes secure and useful progress, reason, without noticing it, uses this as a cover. It sneakily makes assertions of a quite different sort. In these assertions, it adds something entirely foreign to given concepts a priori, without anyone knowing how it was able to do this, and without this question even being allowed to come to mind. I will therefore deal with the distinction between these two kinds of knowledge right at the outset.

On the Difference Between Analytic and Synthetic Judgments

In all judgments where we think about the relationship between a subject and a predicate (I’ll focus on affirmative judgments for now, as applying this to negative ones is easy), this relationship is possible in two different ways:

1. Either the predicate B belongs to the subject A as something that is (hiddenly) contained within the concept of A.
2. Or, the predicate B lies entirely outside the concept of A, though it is certainly connected with it.

In the first case, I call the judgment analytic. In the second, I call it synthetic.

• Analytic judgments (when affirmative) are those where the connection of the predicate to the subject is thought through identity (the predicate is already part of the subject’s definition). One could also call these “judgments of clarification.” They don’t add anything new to the concept of the subject. They only break the subject concept down into its component parts, which were already thought in it (though perhaps confusedly).

  • Example: If I say, “All bodies are extended (take up space).” This is an analytic judgment. I don’t need to go outside the concept of “body” to find that “extension” is connected with it. I only need to analyze the concept of “body” – that is, become aware of the various aspects I always think of as part of “body” – to find this predicate within it.

• Synthetic judgments are those where this connection (between predicate and subject) is thought without identity (the predicate is not part of the subject’s definition). One could also call these “judgments of amplification” (or expansion). They add a predicate to the concept of the subject that was not thought in it at all and could not have been found by analyzing it.

  • Example: If I say, “All bodies are heavy.” In this case, the predicate “heavy” is something entirely different from what I think in the mere concept of “body” in general. Adding such a predicate creates a synthetic judgment.

Key Differences: From this, it’s clear that:

1. Through analytic judgments, our knowledge is not expanded at all. Instead, the concept I already have is just laid out and made more understandable to me.
2. In synthetic judgments, I must have something else (let’s call it X) in addition to the concept of the subject. The understanding relies on this X to recognize that a predicate, which does not lie within the subject’s concept, nevertheless belongs to it.

Where Do We Find “X” in Empirical Judgments? In the case of empirical judgments (judgments of experience), there’s no difficulty finding this X. Here, X is the complete experience of the object that I am thinking about through concept A (where concept A is only part of this experience). For example, although I don’t include the predicate “weight” in the general concept of a “body,” the concept “body” still refers to the complete experience through a part of that experience. I can therefore add other parts of that same experience (like weight) as belonging to the initial concept. I can first understand the concept of “body” analytically through features like extension, impenetrability, shape, etc., which are all thought in this concept. But now I expand my knowledge. Looking back at the experience from which I derived this concept of “body,” I find that weight is also always connected with these other features. Therefore, experience is that X that lies outside the concept A (“body”) and on which the possibility of combining the predicate “weight” (B) with the concept A is based.

The Problem of “X” in Synthetic A Priori Judgments But in synthetic a priori judgments, this help from experience is entirely missing. If I am to go outside concept A to know another concept B as combined with it, what do I depend on? What makes this combination (synthesis) possible, since I don’t have the advantage of looking around for it in the field of experience? Take the proposition: “Everything that happens has its cause.” In the concept of “something that happens,” I am certainly thinking of an existence that was preceded by a time, etc., and analytic judgments can be drawn from that. But the concept of a “cause” means something different from the concept of “something that happens,” and it’s not contained in the idea of “something that happens” at all. How, then, do I come to say something quite different about “that which happens in general”? How do I recognize the concept of “cause” as belonging to it, even though it’s not contained in it? What is the X here, on which the understanding depends when it believes it has discovered a predicate (like “cause”) that is foreign to concept A (“something that happens”) but is still connected with it? It cannot be experience. The principle “Everything that happens has its cause” adds the idea of a cause to the idea of something happening with greater generality than experience can provide. It also adds it with an expression of necessity. Therefore, this principle is entirely a priori and comes from mere concepts. The entire final goal of our theoretical a priori knowledge rests on such synthetic (or ampliative) principles. Analytic judgments are certainly very important and necessary, but only for achieving the clarity of concepts that is required for a secure and extended synthesis – a truly new construction of knowledge.

The Hidden Mystery: How Are Synthetic A Priori Judgments Possible? So, a certain mystery lies hidden here. Only by clearing up this mystery can we make secure and reliable progress in the boundless field of the pure knowledge of the understanding. The task is:

• To uncover the ground for the possibility of synthetic a priori judgments in general.
• To gain insight into the conditions that make every kind of them possible.
• Not merely to give a quick outline of this entire kind of knowledge (which is its own distinct type), but to define it completely and adequately for every use in a system, according to its primary sources, divisions, scope, and boundaries. So much for now about the specific characteristics of synthetic judgments.

The Idea of a Critique of Pure Reason From all of this, the idea of a special science emerges. This science could serve as the critique of pure reason. Any knowledge is called pure if it is not mixed with anything foreign to it. But knowledge is called absolutely pure, in particular, if no experience or sensation at all is mixed into it, making it completely a priori. Now, reason is the faculty that provides the principles of a priori knowledge. Therefore, pure reason is what contains the principles for knowing something absolutely a priori. An organon of pure reason would be a complete set of those principles by which all pure a priori knowledge could be acquired and actually brought about. The full application of such an organon would create a system of pure reason. But that is a very large task. It is still an open question whether such an expansion of our knowledge is possible at all, and in what cases it might be possible. So, we can consider a science that merely evaluates pure reason, its sources, and its boundaries, as a propaedeutic (a preparatory study) to the system of pure reason. Such a thing would not be a doctrine (a body of teachings). It must be called only a critique of pure reason. Its usefulness would initially be only negative: it would serve not for the expansion of our reason, but only for its purification, and for keeping it free from errors. This itself is already a great achievement.

I call all knowledge transcendental that is concerned not so much with objects themselves, but rather with our a priori concepts of objects in general. A system of such concepts would be called transcendental philosophy. But this, again, is too much for a beginning. Such a science would have to completely contain both analytic and synthetic a priori knowledge. As far as our current aim is concerned, that is too broad. We only need to take the analysis as far as is absolutely necessary to understand the principles of a priori synthesis in their entire scope, which is our only concern here. This investigation, which we can properly call not a doctrine but only a transcendental critique, does not aim at expanding knowledge itself but only at correcting it. It is intended to supply the touchstone for judging the value or worthlessness of all a priori knowledge. This is what we are concerned with now. Such a critique is therefore a preparation, if possible, for an organon. If an organon cannot be achieved, then it is at least a preparation for a canon (a set of fundamental principles). In accordance with this canon, the complete system of the philosophy of pure reason – whether it is to consist in expanding its knowledge or merely limiting it – can at least someday be presented both analytically and synthetically.

That such a system should be possible, and indeed that it should not be too large in scope for us to hope to complete it entirely, can be judged in advance. This is because our object is not the nature of things (which is inexhaustible). Our object is the understanding itself, which judges the nature of things. And we are concerned with the understanding only regarding its a priori knowledge. The supply of this a priori knowledge, since we do not need to search for it outside ourselves, cannot remain hidden from us. In all likelihood, it is small enough to be completely recorded, its worth or worthlessness assessed, and subjected to a correct appraisal.

II. Division of Transcendental Philosophy

Transcendental philosophy is, at this stage, only an idea. The critique of pure reason is intended to outline the entire plan for this philosophy architectonically – that is, from principles – with a full guarantee for the completeness and certainty of all the parts that make up this structure. The reason this critique is not itself already called transcendental philosophy rests solely on this: to be a complete system, it would also have to contain an exhaustive analysis of all human a priori knowledge. Now, our critique must certainly lay before us a complete list of all the fundamental concepts that make up the pure knowledge in question.

Introduction (Continued)

II. How This Special Philosophy (Transcendental Philosophy) is Divided (Continued)

What This Critique Will and Won’t Analyze in Detail This critique, however, properly avoids a fully exhaustive analysis of these fundamental concepts themselves. It also doesn’t provide a complete review of all the concepts derived from them. There are two main reasons for this:

1. Such a detailed analysis wouldn’t serve our main purpose. The real difficulty we are tackling in this whole critique is found in synthesis – how different pieces of knowledge are combined – not in the detailed analysis of individual concepts.
2. Trying to achieve complete analysis and derivation of all concepts would go against the unified plan of this work. It’s a responsibility we can be freed from, given our specific goal.

However, this complete analysis of concepts, as well as the derivation of further concepts from these a priori ones, will be easy to do in the future. This will be possible once the principles of synthesis are established as thorough and complete, and if they fully address our essential aim in this critique.

The Critique as an Idea, Not the Full Science Therefore, everything that makes up transcendental philosophy is part of the critique of pure reason. This critique represents the complete idea of transcendental philosophy, but it is not yet that science itself. This is because the critique only goes as far in its analysis as is necessary for the complete evaluation of synthetic a priori knowledge (knowledge that expands our understanding and is known independently of experience).

Keeping Transcendental Philosophy Pure The main goal when dividing up such a science is that absolutely no concepts containing anything empirical (from experience) must be included. The a priori knowledge it deals with must be entirely pure. For this reason, even though the highest principles of morality and its fundamental concepts are a priori knowledge, they do not belong in transcendental philosophy. This is because to discuss morality, one must assume concepts like pleasure and displeasure, desires and inclinations, choice, and so on. All of these concepts originate from experience.

Therefore, transcendental philosophy is a philosophy of pure, merely speculative reason (reason used for theoretical thinking, not practical action). This is because everything practical, insofar as it involves motives for action, is related to feelings. Feelings belong among the empirical sources of knowledge.

Main Parts of This Science Now, if we want to lay out the division of this science from the general viewpoint of any system, the one we will now present must contain two main parts:

1. First, a Doctrine of Elements of pure reason.
2. Second, a Doctrine of Method of pure reason. Each of these main parts will have its own subdivisions, but the reasons for these subdivisions cannot be explained here.

Two Basic Sources of Human Knowledge For now, all that seems necessary for an introduction is to state that there are two sources or “stems” of human knowledge. These may perhaps come from a common root that is unknown to us. These two stems are:

1. Sensibility: This is the faculty through which objects are given to us.
2. Understanding: This is the faculty through which objects are thought by us.

Now, if sensibility were to contain a priori representations (ways of perceiving that exist in the mind before any specific experience), and these representations form the conditions under which objects are given to us, then sensibility would belong to transcendental philosophy.

The transcendental doctrine of the senses (how we perceive things a priori) will have to be the first part of the Doctrine of Elements. This is because the conditions under which the objects of human knowledge are given to us (through sensibility) come before the conditions under which those objects are thought (by the understanding).

Introduction

I. On the Difference Between Pure and Empirical Cognition

How Our Knowledge Begins There is no doubt at all that all our knowledge begins with experience. How else could our ability to know things be awakened and put into action? It happens through objects that stimulate our senses. These objects partly produce our mental images (representations) themselves. They also partly get our understanding moving to compare these images, to connect them, or to separate them. In this way, our understanding works up the raw material of sensory impressions into a knowledge of objects that we call experience. So, as far as time is concerned, no knowledge we have comes before experience. All our knowledge begins when experience begins.

But Does All Knowledge Come From Experience? However, even though all our knowledge starts with experience, it does not therefore mean that all of it comes from or arises out of experience. It could very well be that even our knowledge from experience is a mixture. It might be composed of what we receive through sensory impressions and what our own ability to know (our cognitive faculty) provides from itself. This faculty is merely prompted into action by these sensory impressions. We cannot distinguish this addition from our mind from the fundamental material of our senses until long practice has made us pay attention to it and skilled in separating the two.

The Question of Knowledge Independent of Experience (A Priori Knowledge) Therefore, it is a question that needs closer investigation and should not be dismissed lightly: Is there any knowledge that is independent of all experience, and even independent of all impressions from our senses? We call such knowledge a priori knowledge (meaning knowledge known before or independently of experience). We distinguish it from empirical knowledge, which has its sources a posteriori (meaning after or through experience).

What “A Priori” Truly Means However, the term “a priori” is not yet specific enough to capture the full meaning of the question we are asking. It’s common for people to say that we know many things “a priori” even if that knowledge originally came from experience. This happens when we don’t get the knowledge directly from a new experience, but rather from a general rule that we have, nevertheless, borrowed from experience. For example, someone who digs away the foundation of his house could be said to “know a priori” that it will collapse. He doesn’t need to wait for the actual experience of it falling down. Yet, he could not have known this entirely a priori. He first had to learn from experience that bodies are heavy and therefore fall if their support is removed.

So, in what follows, when we talk about a priori knowledge, we will not mean knowledge that happens independently of this or that specific experience. Instead, we will mean knowledge that occurs absolutely independently of all experience. The opposite of this is empirical knowledge, which is only possible a posteriori, that is, through experience.

Among a priori knowledge, we call knowledge pure if it has absolutely nothing empirical mixed in with it. For example, the statement “Every change has its cause” is an a priori statement. However, it is not pure because “change” is a concept that can only be derived from experience.

II. We Possess Certain A Priori Knowledge, and Even Common Understanding Uses It

Identifying Pure A Priori Knowledge: Necessity and Strict Universality The issue here is finding a way to reliably tell pure knowledge apart from empirical knowledge. Experience teaches us that something is a certain way, but it does not teach us that it could not be otherwise.

So, here are two key indicators:

1. Necessity: If we think of a statement along with its necessity (meaning it must be true), it is an a priori judgment. If, furthermore, this statement is not derived from any other statement except one that is also valid as a necessary statement, then it is absolutely a priori.
2. Strict Universality: Experience never gives its judgments true or strict universality. It only gives us an assumed and comparative universality (based on what we’ve seen so far, through induction). So, properly speaking, experience only allows us to say: “as far as we have observed, there is no exception to this or that rule.” Therefore, if a judgment is thought of with strict universality – meaning no exception whatsoever is considered possible – then it is not derived from experience. Instead, it is valid absolutely a priori.

Empirical universality is therefore just an arbitrary extension of validity. We go from something that holds true in most cases to something that holds true in all cases (for example, the statement “All bodies are heavy”). Strict universality, on the other hand, belongs essentially to a judgment. This points to a special source of knowledge for it: a faculty of a priori knowledge. Necessity and strict universality are therefore secure signs of a priori knowledge, and they always belong together. However, in practice, it is sometimes easier to show that a judgment has empirical limitations (lacks strict universality) than to show it is contingent (lacks necessity). Or, it is often more convincing to show the unrestricted universality we attribute to a judgment than its necessity. Therefore, it is a good idea to use these two criteria – necessity and strict universality – separately, as each one is, by itself, a foolproof indicator.

Examples of Pure A Priori Judgments Now, it is easy to show that such necessary and, in the strictest sense, universal – and therefore pure a priori – judgments actually exist in human knowledge.

• If you want an example from the sciences, you only need to look at any proposition in mathematics.
• If you want an example from the most common use of understanding, the proposition that every change must have a cause will do. Indeed, in this latter case, the very concept of a “cause” so obviously contains the concept of a necessary connection with an “effect” and a strict universality of the rule, that the idea of cause would be entirely lost if one tried, as David Hume did, to derive it from frequent association (seeing one thing happen after another many times) and a resulting habit of connecting ideas (which would only be a subjective, not objective, necessity).

Even without needing such examples to prove that pure a priori principles are real in our knowledge, one could establish their indispensability for the very possibility of experience itself. One could, therefore, establish this a priori. For where would experience itself get its certainty if all the rules it follows were themselves always empirical, and therefore contingent (could be otherwise)? We could hardly allow such contingent rules to count as first principles. For now, however, we can be content with having shown that the pure use of our ability to know is a fact, along with its indicators.

A Priori Concepts It’s not just in judgments, but even in some concepts, that an a priori origin is revealed.

• Think about your concept of a body from experience. Gradually remove everything empirical from it – the color, the hardness or softness, the weight, even its impenetrability (its ability to prevent other things from passing through it). What still remains is the space that was occupied by the body (which has now entirely disappeared). You cannot get rid of the idea of this space.
• Likewise, if you take your empirical concept of any object, whether physical or non-physical, and remove all the properties that experience teaches you about it, you still could not take away from it that by which you think of it as a substance or as something dependent on a substance (even though this concept of substance is more specific than just the concept of an object in general).

Thus, convinced by the necessity with which this concept of substance forces itself upon you, you must admit that it has its origin in your faculty of knowing a priori.

III. Philosophy Needs a Science of A Priori Knowledge

Going Beyond Experience: The Realm of Metaphysics But what is even more significant than all of this is that certain kinds of knowledge even leave the field of all possible experiences. They seem to expand the range of our judgments beyond all limits of experience, using concepts to which no corresponding object can ever be given in experience.

And it is precisely in these latter kinds of knowledge – those that go beyond the world of the senses, where experience can offer neither guidance nor correction – that we find the investigations of our reason. We believe these investigations are far more outstanding in their importance and have a much higher ultimate goal than anything the understanding can learn in the field of appearances. We would rather risk everything, even the chance of being wrong, than give up such important investigations due to any doubts, or out of contempt and indifference. These unavoidable problems of pure reason itself are God, freedom, and immortality. The science whose final aim, in all its preparations, is directed properly only to solving these problems is called metaphysics. The procedure of metaphysics, in the beginning, is dogmatic. That is, it confidently takes on the task of solving these problems without first examining whether reason is capable or incapable of such a great undertaking.

The Neglected Question of Foundations Now, it might seem natural that as soon as one has left the terrain of experience, one would not immediately start building a system with knowledge whose source is unknown. One would not build on the credit of principles whose origin is unknown, without first having made sure of the foundation through careful investigations. Thus, it seems all the more natural that the question should have been raised long ago: How could the understanding come to all this a priori knowledge, and what scope, validity, and value might it have? And indeed, nothing is more natural, if by the word “natural” one means what properly and reasonably ought to happen. But if one means by it what usually happens, then, conversely, nothing is more natural and understandable than that this investigation should have been neglected for so long.

Reasons for Neglecting the Foundations For one part of this a priori knowledge, mathematics, has long been reliable. This creates a favorable expectation about other kinds of a priori knowledge as well, even though these others may be of an entirely different nature. Furthermore, if one is beyond the circle of experience, then one is sure of not being refuted by experience. The charm of expanding one’s knowledge is so great that one can be stopped in one’s progress only by running into a clear contradiction. This, however, one can avoid if one makes one’s inventions carefully, even though they are no less inventions for that. Mathematics gives us a splendid example of how far we can go with a priori knowledge, independently of experience. Now, it is true that mathematics deals with objects and knowledge only so far as these can be presented in intuitions (direct perceptions or mental images). This fact, however, is easily overlooked, since the intuition in question can itself be given a priori (e.g., we can imagine a triangle), and thus can hardly be distinguished from a mere pure concept.

The Drive for Expansion and Plato’s Error Captivated by such a proof of the power of reason, the drive for expansion sees no limits. Imagine a light dove, flying freely and cutting through the air whose resistance it feels. It could get the idea that it could fly even better in empty space, without air. Likewise, Plato abandoned the world of the senses because it set such narrow limits for the understanding. He dared to go beyond it on the “wings of ideas,” into the empty space of pure understanding. He did not notice that he made no headway with his efforts. He had no resistance, no support, so to speak, against which he could brace himself and apply his powers to get his understanding moving.

Building First, Checking Foundations Later: The Role of Analysis It is, however, a common fate of human reason in its theoretical speculations to finish its intellectual building as early as possible. Only then does it investigate whether the ground has been adequately prepared for it. But at that point, all sorts of excuses will be sought to assure us of the building’s sturdiness or, even better, to refuse such a late and dangerous examination. What keeps us free of all worry and suspicion during the construction, however, and flatters us with an appearance of thoroughness, is this: A great part, perhaps the greatest part, of our reason’s business consists in analyzing the concepts that we already have of objects. This provides us with a multitude of pieces of knowledge. Although these are nothing more than illuminations or clarifications of what is already thought in our concepts (though still in a confused way), they are, at least as far as their form is concerned, treasured as if they were new insights. However, they do not extend the concepts that we have in either their matter or content; they only set them apart from each other or make them clearer. Now, since this analytical procedure does yield real a priori knowledge that makes secure and useful progress, reason, without noticing it, uses this as a cover. It sneakily makes assertions of quite another sort. In these assertions, reason adds something entirely alien to given concepts, and indeed does so a priori, without anyone knowing how it was able to do this, and without such a question even being allowed to come to mind. I will therefore deal with the distinction between these two sorts of knowledge right at the outset.

IV. On the Difference Between Analytic and Synthetic Judgments

In all judgments where we think about the relationship between a subject and a predicate (if I consider only affirmative judgments for now, since applying this to negative ones is easy), this relation is possible in two different ways:

1. Either the predicate B belongs to the subject A as something that is (hiddenly) contained within this concept A.
2. Or, the predicate B lies entirely outside the concept A, though it certainly stands in connection with it.

In the first case, I call the judgment analytic. In the second, synthetic.

• Analytic judgments (when affirmative) are thus those in which the connection of the predicate is thought through identity (the predicate is already part of the subject’s meaning). One could also call these judgments of clarification. Through the predicate, they do not add anything new to the concept of the subject. They only break it up by means of analysis into its component concepts, which were already thought in it (though perhaps confusedly).

  • For example, if I say: “All bodies are extended (take up space).” This is an analytic judgment. I do not need to go beyond the concept that I associate with “body” to find that extension is connected with it. Rather, I only need to analyze that concept – that is, become conscious of the various elements that I always think in it – to find this predicate there. It is therefore an analytic judgment.

• Synthetic judgments, on the other hand, are those where this connection is thought without identity. They add to the concept of the subject a predicate that was not thought in it at all, and could not have been extracted from it through any analysis. One could also call these judgments of amplification (or expansion).

  • For example, if I say: “All bodies are heavy.” Here, the predicate (“heavy”) is something entirely different from what I think in the mere concept of a “body” in general. Adding such a predicate creates a synthetic judgment.

Judgments of Experience are All Synthetic Judgments of experience, as such, are all synthetic. It would be absurd to base an analytic judgment on experience. This is because I do not need to go beyond my concept at all to formulate an analytic judgment, and therefore I need no evidence from experience for that. That a body is extended is a proposition that is established a priori; it is not a judgment of experience. Before I even go to experience, I already have all the conditions for my judgment in the concept of “body.” From this concept, I merely draw out the predicate “extended” according to the principle of contradiction (a body that doesn’t take up space is a contradiction). By doing this, I can also become aware of the necessity of the judgment – something experience could never teach me.

On the contrary, although I do not at all include the predicate “weight” in the general concept of a “body,” that concept (“body”) nevertheless refers to an object of experience through some of its features. To this, I can therefore add still other parts of the same experience as belonging with the original features. I can first understand the concept of “body” analytically through the characteristics of extension, impenetrability, shape, etc., all of which are thought in this concept. But now I expand my knowledge. Looking back to the experience from which I originally formed this concept of “body,” I find that weight is also always connected with those other characteristics. I therefore add “weight” synthetically as a predicate to that concept of “body.” It is thus experience on which the possibility of combining the predicate “weight” with the concept “body” is based. This is because both concepts (“body” and “weight”), though one is not contained in the other, nevertheless belong together (though only as a matter of contingent fact, not logical necessity) as parts of a whole. That whole is experience itself, which is a synthetic combination of intuitions (perceptions).

The Challenge of Synthetic A Priori Judgments But in synthetic a priori judgments, this help from experience is entirely lacking. If I am to go beyond concept A to recognize another concept B as combined with it, what do I depend on? By what means does this combination (synthesis) become possible, since I do not have the advantage here of looking around for it in the field of experience? Consider the proposition: “Everything that happens has its cause.” In the concept of “something that happens,” I am certainly thinking of an existence that was preceded by a time, etc., and analytic judgments can be drawn from that. But the concept of a “cause” lies entirely outside that concept of “something that happens.” It indicates something different and is not contained in the representation of “something that happens” at all. How then do I come to say something quite different about “that which happens in general”? How do I recognize the concept of “cause” as belonging to it – indeed, as necessarily belonging to it – even though “cause” is not contained in “something that happens”? What is the unknown = X here, on which the understanding depends when it believes it has discovered, beyond the concept of A, a predicate B that is foreign to A yet which it nevertheless believes to be connected with A? It cannot be experience. The principle “Everything that happens has its cause” adds the idea of cause to the idea of something happening not only with greater generality than experience can provide, but also with the expression of necessity. Therefore, this principle is entirely a priori and comes from mere concepts. Now, the entire final aim of our theoretical a priori knowledge rests on such synthetic (that is, ampliative or knowledge-expanding) principles. Analytic judgments, to be sure, are most important and necessary, but only for achieving that clarity of concepts which is required for a secure and extended synthesis – that is, for a really new acquisition of knowledge.

This study doesn’t try to analyze every single concept in exhaustive detail. It also doesn’t review every idea derived from those concepts. There are two main reasons for this.

First, such a deep analysis of every concept isn’t the main goal here. The real challenge, and the reason for this entire work, is understanding how we combine ideas to form knowledge. The difficulty isn’t in the individual concepts themselves, but in how they come together.

Second, trying to completely analyze and explain the origin of every concept would make this project too big and unfocused. It would go against the plan’s unity. The current aim is more specific, so we don’t need to take on that massive task.

However, this complete analysis of concepts and their origins can still be done easily in the future. This will be possible if the fundamental principles for combining ideas (which this study will provide) are clear and effective. As long as these principles achieve their main goal, filling in the details later won’t be hard.

So, everything that makes up transcendental philosophy is included in this critique of pure reason. This critique represents the complete idea of transcendental philosophy. However, it isn’t the entire science of transcendental philosophy itself. That’s because the critique only goes as deep into analysis as needed to fully understand a specific kind of knowledge: synthetic a priori cognition. This is knowledge that expands our understanding and is gained through reason, not direct experience.

Keeping Knowledge Pure

When we organize a science like this, a primary rule is to include no concepts that have anything empirical (learned from experience). The knowledge must be entirely a priori – meaning it comes from reason alone, pure and untainted by experience.

This has an important consequence. Even though the highest principles of morality and its basic concepts are known through reason (a priori), they don’t belong in transcendental philosophy. Here’s why:

• Moral principles don’t use ideas like pleasure, pain, desires, or inclinations (which all come from experience) as their foundation.
• However, when building a system of pure morality, these empirical ideas must be included in the concept of duty. Duty often involves overcoming an obstacle (like a desire) or resisting an attraction that shouldn’t become a motive.

Therefore, transcendental philosophy is a philosophy of pure, purely theoretical reason. It’s not about practical matters. Anything practical, especially if it involves incentives or motivations, is connected to feelings. Feelings come from our experiences, so they are empirical sources of knowledge, not pure reason.

Structuring This Science

If we want to outline this science systematically, like any organized system, it must have two main parts:

1. First, a Doctrine of Elements: This part will explore the basic building blocks of pure reason.
2. Second, a Doctrine of Method: This part will explain how to use pure reason correctly.

Each of these main parts will have its own subdivisions. However, the reasons for these specific subdivisions cannot be explained just yet.

For now, as an introduction, it’s enough to say this: human knowledge seems to come from two main sources. These might even grow from a single, common root that we don’t yet know. These two sources are:

• Sensibility: This is how objects are given to us, how we perceive them.
• Understanding: This is how objects are thought by us, how we make sense of them.

Now, if our capacity for sensing things (sensibility) involves any a priori concepts – fundamental ideas that are necessary conditions for us to even perceive objects – then sensibility will be part of transcendental philosophy. If this is the case, the study of these a priori aspects of our senses (the transcendental doctrine of the senses) will belong to the first part of our science, the Doctrine of Elements. This is because the ways we receive information about objects (the conditions of sensibility) come before the ways we think about those objects (the conditions of understanding).

I. Transcendental Doctrine of Elements

This is the first main part of our study. It’s called the Transcendental Doctrine of Elements.

In this section, we will explore the basic building blocks of our knowledge. We’re specifically looking at the “transcendental” components. This means we are focusing on parts of knowledge that don’t come from our senses or everyday experiences. Instead, they come from the way our minds are structured to understand things. These are the fundamental “elements” that make our knowledge possible in the first place.

The Transcendental Doctrine of Elements First Part The Transcendental Aesthetic1,1[A 19/B 33]

We are now entering the first part of the Transcendental Doctrine of Elements. This part is called the Transcendental Aesthetic. “Aesthetic” here refers to our senses and how we perceive things, not art or beauty. “Transcendental” means we’re looking at the conditions that make our experience possible, specifically those that exist in our minds before any particular experience. So, the Transcendental Aesthetic studies the basic principles of how we sense and perceive the world a priori (independently of experience).

How We Connect with Objects: Intuition and Sensibility

No matter how we gain knowledge about objects, the most direct way our minds connect with them is through intuition. Think of intuition as an immediate, direct awareness of something. All our thinking, in some way, aims at this direct awareness as its final goal.

However, this intuition only happens if an object is actually given to us. This, in turn, is only possible if the object affects our mind in a certain way. The ability of our mind to receive mental representations when we are affected by objects is called sensibility. Sensibility is like our mind’s capacity to be open to receiving information from the world.

So, objects are given to us through our sensibility. Sensibility alone provides us with these direct awarenesses or intuitions. Once we have intuitions, we then think about them using our understanding. It’s from our understanding that concepts arise.

But all thinking, whether it’s straightforward or takes a more roundabout path, must ultimately connect back to intuitions. For us humans, this means all our thoughts must connect back to our sensibility. Why? Because there’s no other way for objects to be given to us.

Sensation and Appearance

When an object affects our ability to have representations, this effect is called sensation. For example, the feeling of warmth from the sun is a sensation. An intuition that is related to an object through sensation is called an empirical intuition (meaning it’s based on experience). The object of an empirical intuition, before our understanding has fully defined it with concepts, is called an appearance. It’s how the object appears to us.

Matter and Form in Appearances

In any appearance, we can distinguish two aspects:

1. Matter: This is the part of the appearance that corresponds to sensation. It’s the raw data from our senses, like the colors, sounds, or textures we experience. Matter is given to us a posteriori – meaning through experience.
2. Form: This is what allows the variety of an appearance (its manifold) to be perceived as organized or ordered in certain ways. For example, seeing multiple objects arranged in a particular layout. Since the “container” or structure in which sensations are ordered cannot itself be another sensation, this form must not come from sensation. Instead, the form of all appearances must already be present in our mind a priori – before any specific experience. Therefore, we can think about this form separately from all sensation.

Pure Intuition: Form Without Sensation

I call any mental representation pure (in a transcendental sense) if it contains nothing that comes from sensation. Following this, the pure form of our sensible intuitions – the underlying structure for how we sense things – must exist in our mind a priori. This pure form is where all the diverse content of appearances gets ordered. This pure form of sensibility is also called pure intuition.

Let’s make this clearer: Imagine you have a representation of a physical object, like a ball.

• First, mentally remove everything your understanding thinks about it: concepts like “substance,” “force,” “divisibility.”
• Next, mentally remove everything that belongs to sensation: qualities like “impenetrable,” “hard,” “red.”

Even after removing all these, something from your original empirical intuition of the ball is still left: its extension (the space it takes up) and its shape. These aspects – extension and form – belong to pure intuition. Pure intuition happens a priori, even without a real object currently present to our senses or any active sensation. It exists as a fundamental way our sensibility is structured in our minds.

Transcendental Aesthetic: The Science of Pure Sensibility

I call the science that studies all the a priori principles of our sensibility the transcendental aesthetic. Such a science must exist. It forms the first part of the broader “Transcendental Doctrine of Elements.” It stands in contrast to the part that deals with the principles of pure thinking, which is called “Transcendental Logic.”

What We Do in Transcendental Aesthetic

In the Transcendental Aesthetic, our investigation will proceed in two steps:

1. First, we will isolate sensibility. We do this by separating everything that the understanding thinks using its concepts. After this, only empirical intuition (raw, sensed experience) remains.
2. Second, from this empirical intuition, we will detach everything that belongs to sensation (like color, hardness, etc.). When we do this, nothing is left except pure intuition and the mere form of appearances. This form is the only thing that our sensibility can provide a priori.

Through this investigation, we will find that there are two pure forms of sensible intuition. These act as a priori principles for our knowledge. These two forms are space and time. We will now examine these.

The Transcendental Aesthetic: First Section – On Space

How We Represent Objects in Space

We have something called outer sense, which is a property of our mind. By means of this outer sense, we represent objects as being outside of ourselves. Crucially, we represent all of them as existing in space. It is in space that their shape, size, and relationship to one another are determined or can be determined.

We also have an inner sense. Through inner sense, our mind is aware of itself or its own internal state. Inner sense doesn’t give us an intuition of the soul itself as an object. However, it does provide a specific form under which we can be aware of our inner state. This means everything related to our inner thoughts and feelings is represented in relationships of time.

Just as time cannot be perceived externally (as something outside us), space cannot be perceived as something inside us (like a thought or feeling).

What Are Space and Time?

So, what exactly are space and time?

• Are they actual existing things, like objects?
• Are they just properties or relations of things that would exist even if we weren’t perceiving them?
• Or, are they relations that only belong to the form of our intuition – meaning they are part of the subjective makeup of our own minds, without which we couldn’t attribute these properties (like “being in space”) to anything at all?

To figure this out, let’s first consider space.

Arguments About Space

1. Space is not learned from experience. Space is not an empirical concept that we get from outer experiences. For me to relate certain sensations to something outside of me (meaning, to something in a different place in space from where I am), I must already have a representation of space. For me to see objects as outside one another, and not just different but in different places, the idea of space must already be there as a foundation. Therefore, we don’t get the representation of space from observing the relations between outer appearances through experience. Instead, outer experience itself is only possible because we already have this representation of space.

2. Space is a necessary, a priori foundation for perception. Space is a necessary representation that exists a priori (before experience). It is the ground for all our outer intuitions (our direct awareness of external things). You can never imagine that there is no space. However, you can easily think of space as empty, with no objects in it. Therefore, space should be seen as the condition that makes appearances possible, not as some feature that depends on them. It is an a priori representation that necessarily underlies all outer appearances.

3. The certainty of geometry depends on space being a priori. The absolute certainty of all geometrical principles (like “the shortest distance between two points is a straight line”) and the possibility of constructing geometrical figures a priori (without needing to measure actual objects) are based on this a priori necessity of space. If our representation of space were a concept we learned a posteriori (from general outer experience), then the basic principles of mathematics and geometry would just be observations. They would be as uncertain as any perception. It wouldn’t be necessarily true that only one straight line lies between two points; experience would just teach us that it usually does. Things learned from experience only have a kind of general truth based on what we’ve seen so far (inductive reasoning). We could only say, “as far as we’ve observed, no space has been found with more than three dimensions.” But geometry claims its truths are absolutely necessary.

4. Space is a pure intuition, not a general concept. Space is not a discursive (or general) concept about how things relate in general. It is a pure intuition. Here’s why: First, you can only represent one single space. When we talk about “many spaces,” we just mean parts of one and the same unique, all-encompassing space. These parts don’t come before the single, whole space as if they were components that could be assembled to make it. Instead, parts are only thought of within the one space. Space is essentially single. The variety within it (and thus the general concept of “spaces”) comes from imposing limitations on this single space. From this, it follows that an a priori intuition (one that is not empirical) is the foundation for all our concepts about space. This is also why all geometrical principles (e.g., in a triangle, any two sides added together are always greater than the third side) are never derived from general concepts like “line” or “triangle.” Instead, they are derived from intuition, and specifically, they are derived a priori with absolute certainty.

5. Space is represented as infinitely large. Space is represented as a given, infinite magnitude. A general concept of “space” (which could apply equally to a small area like a foot, or a larger one like a mile) cannot tell us anything about its overall size. If our intuition of space didn’t have this characteristic of being boundless as we explore it in our minds, then no concept of relationships between spaces could ever give us a principle that these relationships are infinite.

Conclusions About Space

From these points, we can draw the following conclusions:

a)  **Space is not a property of things in themselves.**
    Space does not represent any property of things as they are in themselves, nor does it represent any relation between them as they are in themselves. It’s not a characteristic that attaches to objects themselves and that would remain even if we were to ignore all the subjective conditions of how we perceive (our intuition). This is because neither absolute properties (like "this thing *is* X") nor relative properties (like "A is next to B") can be intuited *before* the existence of the things they belong to. So, such properties cannot be intuited *a priori*.

b)  **Space is the form of our outer sense.**
    Space is nothing other than the form of all appearances of our outer sense. It is the subjective condition of our sensibility, under which alone outer intuition is possible for us.
    Now, because our capacity to be affected by objects (our receptivity) must necessarily exist *before* any intuitions of these objects, we can understand something crucial: The form of all appearances (space) can be present in our mind *before* any actual perceptions, meaning it's there *a priori*. And as a pure intuition in which all objects must be arranged, it can contain the principles of their relationships *before* we have any experience of them.

The Human Standpoint on Space

Therefore, we can talk about space, extended objects, and so on, only from a human standpoint. If we set aside the subjective condition under which alone we can have outer intuition – namely, our particular way of being affected by objects – then the representation of space means nothing at all. This characteristic (being “in space”) is attributed to things only insofar as they appear to us, meaning they are objects of our sensibility.

The constant form of this receptivity, which we call sensibility, is a necessary condition for all the relationships in which objects can be perceived as outside us. If we mentally subtract these objects, what remains is this pure intuition, which we call space.

We cannot make the special conditions of our sensibility (like space) into conditions for the possibility of things in themselves. We can only make them conditions for the possibility of their appearances to us. So, we can correctly say that space includes all things that may appear to us externally. But we cannot say that space includes all things in themselves, whether they are intuited or not, or by whatever kind of mind they might be intuited. We simply cannot judge whether the intuitions of other thinking beings (if they exist) are bound by the same conditions that limit our intuition and that are universally valid for us.

If we add a limitation to a judgment related to the subject experiencing it, then the judgment becomes unconditionally valid. For example, the statement “All things are next to one another in space” is valid only under the limitation that these things are taken as objects of our sensible intuition. If I refine this and say: “All things, as outer intuitions, are next to one another in space,” then this rule is valid universally and without any further limitation.

Our explanations, therefore, show the reality (meaning, objective validity) of space concerning everything that can come before us externally as an object. But at the same time, they show the ideality of space concerning things when they are considered in themselves by reason (that is, without taking into account the structure of our sensibility). So, we assert the empirical reality of space (it’s real with respect to all possible outer experience). However, we also assert its transcendental ideality (it’s nothing as soon as we leave out the condition of the possibility of all experience – our sensibility – and consider space as something that grounds things in themselves).

Space Compared to Other Subjective Perceptions

Besides space, there is no other subjective representation that relates to something external that could be called a priori objective. Therefore, this subjective condition for all outer appearances (space) cannot be compared with just any other subjective perception.

For example:

• The pleasant taste of a wine doesn’t belong to the objective properties of the wine itself (even if we consider the wine as an appearance). Instead, it belongs to the particular way the sense of taste is constituted in the person enjoying it.
• Colors are not objective qualities of the physical objects to which they are attached when we see them. They are only modifications of our sense of sight, which is affected by light in a certain way.

Space, however, is different. As a condition for outer objects, it necessarily belongs to their appearance or intuition. Taste and colors are by no means necessary conditions under which alone objects can be objects of the senses for us. They are only combined with an appearance as contingently added effects of our particular biological organization. So, they are not a priori representations; they are based on sensation. A pleasant taste is even based on feeling (pleasure or displeasure) as an effect of sensation.

No one can have an a priori representation of a color or any taste. But space concerns only the pure form of intuition. It includes no sensation (nothing empirical) in itself. All kinds and determinations of space (like shapes and relations) can and even must be able to be represented a priori if concepts of shapes and relations are to arise. It is only through space that it’s possible for things to be outer objects for us.

The Purpose of This Distinction

The point of this discussion is to prevent anyone from trying to illustrate the asserted ideality of space with completely inadequate examples. Things like colors and taste are correctly considered not as qualities of things, but as mere alterations of our subjective experience, which can even be different in different people. In such examples, that which is originally itself only an appearance (e.g., a rose) is treated in an empirical sense as a thing in itself, even though it can appear different to every eye regarding its color.

The transcendental concept of appearances in space, on the other hand, is a critical reminder: absolutely nothing that is intuited in space is a thing in itself. Space is not a form that belongs to anything in itself. Rather, objects in themselves are not known to us at all. What we call outer objects are nothing other than mere representations of our sensibility. The form of this sensibility is space. The true correlate of these representations – the thing in itself – is not and cannot be known through them, nor is it ever something we inquire about in experience.

The Transcendental Aesthetic: Second Section – On Time

Now, let’s consider time.

Arguments About Time

1. Time is not learned from experience. Time is not an empirical concept that is somehow drawn from experience. For the perceptions of things happening at the same time (simultaneity) or one after another (succession) wouldn’t even occur if the representation of time did not ground them a priori. Only by presupposing time can one represent that several things exist at one and the same time (simultaneously) or in different times (successively).

2. Time is a necessary, a priori foundation for all intuitions. Time is a necessary representation that grounds all intuitions (both inner and outer). Regarding appearances in general, you cannot remove time, though you can very well take appearances away from time (imagine time passing with nothing happening). Therefore, time is given a priori. In time alone is all actuality of appearances possible. Appearances could all disappear, but time itself, as the universal condition of their possibility, cannot be removed.

3. The a priori necessity of time grounds principles about time. This a priori necessity of time also grounds the possibility of absolutely certain principles about the relations of time, or axioms of time in general. Time has only one dimension: different times are not simultaneous but successive (just as different spaces are not successive but simultaneous). These principles could not be drawn from experience, because experience would give us neither strict universality nor absolute certainty. We would only be able to say: “This is what common perception teaches,” but not: “This is how matters must stand.” These principles are valid as rules under which experiences are possible at all. They instruct us before experiences, not through them.

4. Time is a pure form of sensible intuition, not a general concept. Time is not a discursive or, as one calls it, general concept. It is a pure form of sensible intuition. Different times are only parts of one and the same time. However, a representation that can only be given through a single object (or in this case, a single, all-encompassing framework) is an intuition. Furthermore, the proposition that different times cannot be simultaneous cannot be derived from a general concept. This proposition is synthetic (it adds new information not contained in the concept of “different times”) and cannot arise from concepts alone. It is therefore immediately contained in the intuition and representation of time.

5. The infinitude of time means it’s a single, grounding framework. The infinitude of time means nothing more than that every specific, determined length of time (like an hour or a day) is only possible through limitations of a single, grounding time. The original representation, time, must therefore be given as unlimited. When the parts themselves and every magnitude of an object can only be definitely represented through limitation, then the entire representation cannot be given through concepts (because then the partial representations would come first). Instead, their immediate intuition must be the ground.

Conclusions About Time

From these concepts, we can draw the following conclusions:

a)  **Time is not something that exists by itself or as an objective property of things.**
    Time is not something that would exist on its own, nor does it attach to things as an objective determination that would remain if one abstracted from all subjective conditions of our intuition of them. If time were something existing on its own (the first case), it would be something that was actual yet without any actual object filling it.

Okay, let’s continue our conclusions about time.

Previously, in point (a), we said that if time were something existing on its own, it would be actual without any actual object in it. Now, regarding the second possibility (that time is an objective property or order attaching to things themselves): Time could not come before objects as their own built-in condition or order, and then be known and directly perceived a priori through propositions that expand our knowledge. However, this can happen if time is nothing more than the subjective condition under which all direct awareness (intuitions) can take place in us. If this is true, then this form of our inner intuition (time) can be represented before we experience objects, and therefore a priori.

b)  **Time is the form of our inner sense.**
    Time is nothing other than the form of our **inner sense**. This means it's the structure of how we are aware of ourselves and our own inner state (our thoughts, feelings, etc.).
    Time cannot be a characteristic of outer appearances. It doesn't belong to a shape or a position in space. Instead, time determines the relationship between representations *within our inner state*.
    And precisely because this inner awareness (our inner intuition) doesn't provide us with any shape, we try to make up for this lack by using analogies. We often represent the sequence of time as a line progressing infinitely. On this line, the variety of moments forms a series that has only one dimension (length). We then infer all the properties of time from the properties of this line. There's only one key difference: the parts of the line exist all at once (simultaneously), but the parts of time always exist one after another (successively).
    From this, it's also clear that the representation of time is itself an **intuition** (a direct awareness), because all its relations can be expressed in an outer intuition (like the line).

c)  **Time is the *a priori* formal condition for all appearances in general.**
    Space, as the pure form of all *outer* intuitions, is limited as an *a priori* condition only to those outer intuitions.
    However, *all* our representations – whether they have outer things as their object or not – belong to our inner state because they are, after all, determinations of our mind. This inner state, in turn, falls under the formal condition of inner intuition, which is **time**.
    Therefore, time is an *a priori* condition for *all appearance in general*. It is the immediate condition for inner appearances (of our souls or minds). And because outer appearances eventually become representations in our inner state, time is also the indirect (mediate) condition for outer appearances.
    So, if I can say *a priori* that "all outer appearances are in space and are determined *a priori* according to the relations of space," then, based on the principle of inner sense, I can say more broadly: "all appearances in general (i.e., all objects of the senses) are in time, and necessarily exist in relations of time."

Time is Real for Experience, but Not for Things in Themselves

If we could step away from our particular way of inwardly sensing ourselves – and through this inner sense, also processing all outer intuitions – and if we could thus consider objects as they might be in themselves, then time would be nothing.

Time only has objective validity when it comes to appearances – because appearances are already things we perceive as objects of our senses. But time is no longer objective if we ignore the sensibility of our intuition (our specific way of perceiving, which is unique to us) and speak of “things in general” or “things in themselves.”

So, time is merely a subjective condition of our human intuition. Our intuition is always “sensible,” meaning it happens when we are affected by objects. In itself, outside of the subject (us), time is nothing.

Nevertheless, time is necessarily objective concerning all appearances. This means it’s objective for all things that can ever come before us in experience. We cannot say, “All things are in time,” because when we talk about “things in general,” we are abstracting away from any particular kind of intuition of them. But our specific kind of intuition is the very condition that makes time relevant to our representation of objects. Now, if we add this condition to the concept, and state the principle as: “All things as appearances (as objects of sensible intuition) are in time,” then this principle has solid objective correctness and a priori universality.

Our statements, accordingly, teach the empirical reality of time. This means time has objective validity concerning all objects that may ever be given to our senses. And since our intuition is always sensible, no object can ever be given to us in experience that does not fall under the condition of time. But, on the other hand, we reject any claim that time has absolute reality. We deny that it would attach to things absolutely, as a condition or property, even without considering the form of our sensible intuition. Such properties, which would belong to things in themselves, can never be given to us through the senses.

This, therefore, is what we mean by the transcendental ideality of time. According to this idea, if one ignores the subjective conditions of sensible intuition, time is nothing at all. It cannot be counted as either existing on its own (subsisting) or as a property within objects themselves (inhering), separate from their relation to our intuition. Yet, this ideality of time should not be compared to misperceptions of sensation (like thinking the greenness of a leaf is in the leaf itself apart from our seeing it), just as the ideality of space shouldn’t be. In those cases of misperception, one assumes that the appearance itself (like the green leaf) has objective reality as a thing in itself, which is not what we’re saying here about time in a transcendental sense. Here, the object itself is regarded merely as an appearance. (You can refer to the remark in the previous section about space for more on this.)

Further Explanation (Elucidation) on Time

Some insightful people have unanimously raised an objection against this theory, which grants empirical reality to time but disputes its absolute and transcendental reality. I conclude that this objection must naturally occur to every reader who is not used to these kinds of considerations.

The objection goes like this: “Changes are real. (This is proven by the change of our own mental representations, even if one were to deny all outer appearances and their changes.) Now, changes are possible only in time. Therefore, time is something real.”

There is no difficulty in answering this. I admit the entire argument. Time is certainly something real; namely, it is the real form of inner intuition. It therefore has subjective reality with regard to inner experience. That is, I really do have the representation of time and of my own states (my determinations) within it. Therefore, time should be regarded not as an object itself, but as the way of representing myself as an object.

But if I, or any other being, could be aware of myself without this condition of sensibility (time), then these very same states, which we now represent to ourselves as changes, would give us a kind of knowledge in which the representation of time, and therefore also of change, would not occur at all. So, its empirical reality remains as a condition of all our experiences. Only absolute reality cannot be granted to it, based on what we’ve discussed. Time is nothing except the form of our inner intuition. If one removes the special condition of our sensibility from it, then the concept of time also disappears. It does not stick to the objects themselves, but only to the subject that intuits them.

The reason this objection is made so unanimously, even by those who don’t have convincing arguments against the ideality of space, is this: They didn’t expect to be able to prove the absolute reality of space with complete certainty because they were faced with idealism. Idealism suggests that the reality of outer objects cannot be strictly proven. On the contrary, the reality of the object of our inner sense (of myself and my state) seems immediately clear through consciousness. Outer objects could be mere illusions, but our inner state, in their opinion, is undeniably something real.

However, they didn’t consider that both inner and outer states, while their reality as representations isn’t disputed, still belong only to appearance. Appearance always has two sides:

1. One side where the object is considered in itself (without regard to the way it is intuited; the nature of this object in itself must therefore always remain problematic and unknown).
2. The other side where the form of the intuition of this object is considered. This form must not be sought in the object in itself, but in the subject to whom it appears. Nevertheless, this form really and necessarily pertains to the representation of this object.

Space and Time as Sources of Knowledge

Accordingly, space and time are two sources of knowledge from which different kinds of synthetic knowledge (knowledge that expands our understanding) can be drawn a priori. Pure mathematics provides a splendid example of this, especially concerning knowledge of space and its relations.

Taken together, space and time are the pure forms of all sensible intuition. They thereby make synthetic a priori propositions possible. But these a priori sources of knowledge also determine their own boundaries by the very fact that they are merely conditions of sensibility. Their boundary is that they apply to objects only as far as objects are considered as appearances. They do not present things as they are in themselves. Appearances alone are the field of their validity; beyond this field, no further objective use of them can take place.

This reality of space and time (as forms of our intuition) leaves the certainty of experiential knowledge untouched. We are just as certain of our experiences whether these forms necessarily stick to the things in themselves or only to our intuition of these things.

However, those who assert the absolute reality of space and time (whether they assume space and time exist on their own or are just properties inherent in things) must come into conflict with the principles of experience.

• If they choose the first option (that space and time exist on their own – generally the position of mathematical investigators of nature), then they must assume two eternal and infinite self-subsisting non-entities (space and time). These non-entities supposedly exist (yet without there being anything real in them) only to contain everything real within themselves.
• If they adopt the second position (as some metaphysicians of nature do), and hold that space and time are relations of appearances (next to or successive to one another) that are abstracted from experience (though confusedly represented in this abstraction), then they must dispute the validity, or at least the absolute certainty, of a priori mathematical doctrines concerning real things (e.g., things in space). They must do this because this certainty does not come from experience (a posteriori). On their view, the a priori concepts of space and time are only creations of the imagination. The origin of these concepts would really have to be sought in experience, from whose abstracted relations the imagination has made something that, while containing what is general in them, cannot exist without the restrictions that nature has attached to them.

The first group (mathematical investigators) succeeds in opening the field of appearances for mathematical statements. However, they themselves become very confused by these very conditions (space and time as self-subsisting non-entities) if the understanding tries to go beyond this field of appearances. The second group (metaphysicians of nature) succeeds, with respect to going beyond appearances, in that their representations of space and time do not stand in their way if they want to judge objects not as appearances but merely in relation to the understanding. However, they can neither offer any ground for the possibility of a priori mathematical knowledge (since they lack a true and objectively valid a priori intuition for space and time), nor can they bring the propositions of experience into necessary agreement with those mathematical assertions.

On our theory of the true nature of these two original forms of sensibility (space and time), both these difficulties are resolved.

Why Only Space and Time?

Finally, it is clear that the transcendental aesthetic cannot contain more than these two elements, namely space and time. This is because all other concepts belonging to sensibility – even the concept of motion, which unites both elements – presuppose something empirical. Motion, for instance, presupposes the perception of something movable. In space considered in itself, there is nothing movable. Therefore, the movable must be something that is found in space only through experience; it is an empirical datum. In the same way, the transcendental aesthetic cannot count the concept of alteration among its a priori data. Time itself does not alter; only something that is within time alters. For this, the perception of some existence and the succession of its states (its determinations) is required – in other words, experience.

General Remarks on the Transcendental Aesthetic

First, it will be necessary to explain our opinion about the fundamental nature of sensible knowledge in general as clearly as possible, to prevent any misinterpretation.

We have wanted to say that all our intuition is nothing but the representation of appearance.

• The things that we intuit are not, in themselves, what we intuit them to be.
• Nor are their relations constituted in themselves as they appear to us.
• If we remove our own subject (our mind), or even just the subjective constitution of our senses in general, then all the constitution, all relations of objects in space and time – indeed space and time themselves – would disappear.
• As appearances, they cannot exist in themselves, but only in us.

What may be the case with objects in themselves, abstracted from all this receptivity of our sensibility, remains entirely unknown to us. We are acquainted with nothing except our way of perceiving them. This way is peculiar to us, and therefore does not necessarily pertain to every being, though it certainly pertains to every human being. We are concerned solely with this. Space and time are its pure forms; sensation in general is its matter.

• We can know the pure forms (space and time) a priori, i.e., before any actual perception. They are therefore called pure intuition.
• The matter (sensation), however, is what makes our knowledge a posteriori cognition, i.e., empirical intuition. The pure forms adhere to our sensibility absolutely necessarily, whatever sort of sensations we may have. The sensations themselves can be very different.

Even if we could bring this intuition of ours to the highest degree of distinctness, we would not thereby come any closer to the constitution of objects in themselves. We would, in any case, still only completely know our own way of intuiting, i.e., our sensibility. And this knowledge would always be only under the conditions originally depending on the subject: space and time. What the objects may be in themselves would still never be known through the most enlightened cognition of their appearance, which is all that is ever given to us.

Therefore, the idea that our entire sensibility is nothing but a confused representation of things, which solely contains what pertains to them in themselves but only under a heap of marks and partial representations that we can never consciously separate, is a falsification of the concept of sensibility and of appearance. It renders the entire theory of them useless and empty. The difference between an indistinct and a distinct representation is merely logical; it does not concern the content or origin. Without doubt, the concept of “right” (as in justice) that is used by common sense contains the very same things that the most subtle speculation can develop out of it. It’s just that in common and practical use, one is not conscious of these many underlying representations within these thoughts. Thus, one cannot say that the common concept of right is “sensible” and contains a mere “appearance,” because right cannot appear at all. Rather, its concept lies in the understanding and represents a constitution (the moral constitution) of actions that pertains to them in themselves. The representation of a physical body in intuition, on the contrary, contains nothing at all that could pertain to an object in itself. It merely contains the appearance of something and the way in which we are affected by it. This receptivity of our cognitive capacity is called sensibility, and it remains worlds apart from the cognition of the object in itself, even if one might see through to the very bottom of the appearance.

The Leibnizian-Wolffian philosophy, therefore, directed all investigations of the nature and origin of our cognitions to an entirely incorrect point of view. It did so by considering the distinction between sensibility and the intellectual (or understanding) as merely logical (a matter of clearness or confusion). However, the distinction is obviously transcendental. It does not concern merely the form of distinctness or indistinctness, but its origin and content. So, through sensibility, we do not cognize the constitution of things in themselves merely indistinctly; rather, we do not cognize them at all. As soon as we take away our subjective constitution (our specific way of sensing), the represented object, along with the properties that sensible intuition attributes to it, is nowhere to be found, nor can it be encountered. This is because it is precisely this subjective constitution that determines its form as an appearance.

We ordinarily distinguish quite well between that which is essentially attached to the intuition of appearances and is valid for every human sense in general, and that which pertains to them only contingently (by chance). The contingent kind is not valid for sensibility in general but only for a particular situation or organization of this or that sense. And so, one calls the first kind of cognition one that represents the object in itself, but the second kind only its appearance. This distinction, however, is only empirical.

Let’s continue our general remarks on the Transcendental Aesthetic (our study of how we sense things).

If you stick with the common way of thinking, you might not realize that our everyday, empirical intuition (our direct awareness of things through the senses) is itself just an appearance. If you don’t see that this appearance doesn’t actually show you anything about a “thing in itself,” then our important transcendental distinction is lost. We would then mistakenly believe we are getting to know things as they truly are in themselves. But the truth is, in the world of sense, we only ever deal with appearances, even when we are deeply researching objects.

For example, we would certainly call a rainbow a mere appearance that occurs during a sun-shower. We might then call the rain itself “the thing in itself.” This is correct, as long as we understand “thing in itself” here in a purely physical sense. In this physical sense, the rain is something that, in universal experience and from all different viewpoints relative to our senses, is always perceived in a consistent way.

But let’s consider this empirical object (the rain) in a more general way. Without focusing on whether it appears the same way to every human sense, let’s ask: does this rain represent an object in itself? (We’re not talking about the individual raindrops here, because as appearances, they are already empirical objects.) This question – about the relationship between our representation (our idea of rain) and the object in itself – is a transcendental question. From this transcendental viewpoint, not only are the raindrops mere appearances, but even their round form, and indeed even the space through which they fall, are nothing in themselves. They are only modifications or fundamental structures of our sensible intuition (our way of sensing). The transcendental object – the underlying thing in itself – however, remains unknown to us.

The Certainty of Our Theory

The second important goal of our Transcendental Aesthetic is not just to gain some acceptance as a believable hypothesis. It must be as certain and unquestionable as can ever be demanded of a theory that is meant to be a fundamental tool for understanding (an “organon”). To make this certainty fully convincing, we will choose a case where its validity can become obvious.

Geometry as Proof

Let’s suppose for a moment that space and time are objective in themselves and are conditions for the possibility of things as they are in themselves. If this were true, we would first see that there are many propositions about both space and time – but especially about space – that are known a priori (without experience), are absolutely certain (“apodictic”), and expand our knowledge (“synthetic”). We will use space as our main example here. The propositions of geometry are known synthetically, a priori, and with absolute certainty. So, I ask: Where do you get such propositions from? And what does our understanding rely on to reach such absolutely necessary and universally valid truths?

There are only two ways:

1. Through concepts.
2. Through intuitions (direct awareness). Both of these are given either a priori (before experience) or a posteriori (from experience).

Let’s look at a posteriori sources: Empirical concepts, along with what they are based on (empirical intuition), cannot produce any synthetic proposition except one that is also merely empirical – an observation from experience. Such a proposition can never contain the kind of necessity and absolute universality that is characteristic of all propositions in geometry.

So, geometric knowledge must come from a priori sources – either through mere concepts or through a priori intuitions. It’s clear that from mere concepts alone, no synthetic knowledge (knowledge that expands understanding) can be achieved, only analytic knowledge (knowledge that clarifies concepts).

• Take the proposition: “With two straight lines, no space at all can be enclosed, so no figure is possible.” Try to derive this from just the concept of “straight lines” and the number “two.”
• Or take the proposition: “A figure is possible with three straight lines.” Try to derive this from these concepts alone.

All your effort will be in vain. You will see that you are forced to turn to intuition, as geometry always does. So, you give yourself an object in intuition. But what kind of intuition is this? Is it a pure a priori intuition or an empirical one?

• If it were empirical, then no universally valid, let alone absolutely certain, proposition could ever come from it. Experience can never provide that kind of certainty.

Therefore, you must give yourself the object a priori in intuition, and base your synthetic proposition on this. This leads to some crucial points:

• If there wasn’t a built-in capacity in you for intuiting a priori;
• If this subjective condition related to form (how you intuit) were not at the same time the universal a priori condition under which alone the object of this (outer) intuition (like a triangle) is itself possible;
• If the object (the triangle) were something existing in itself, without any relation to you as the subject (the observer); …then how could you say that what necessarily lies in your subjective conditions for constructing a triangle must also necessarily belong to the triangle in itself? You couldn’t add something new (the figure) to your concept (of three lines) that must then necessarily be found in the object, because this object would be given before your knowledge of it and not through your act of knowing.

Therefore, if space (and time as well) were not a mere form of your intuition – a form that contains a priori conditions under which alone things could be outer objects for you, and these objects are nothing in themselves without these subjective conditions – then you could make absolutely no synthetic and a priori statements about outer objects.

It is therefore indubitably certain, and not merely possible or even probable, that space and time, as the necessary conditions of all experience (both outer and inner), are merely subjective conditions of all our intuition. In relation to these subjective conditions, therefore, all objects are mere appearances, and not things given “for themselves” or “as they are in themselves.” Furthermore, much can be said a priori about the form of these appearances, but nothing whatsoever about the things in themselves that may ground them.

The Transcendental Doctrine of Elements First Part The Transcendental Aesthetic 1[A 19/B 33]

We are now looking at the first main part of the Transcendental Doctrine of Elements. This part is called the Transcendental Aesthetic. The term “aesthetic” here relates to our senses and how we perceive things. “Transcendental” means we’re studying the basic conditions in our minds that make experience possible, conditions that exist before any specific experience. So, the Transcendental Aesthetic is the study of the fundamental principles of how we sense the world, known a priori (independently of experience).

How We Connect with Objects: Intuition and Sensibility

No matter how we learn about objects, our minds connect with them most directly through intuition. Think of intuition as an immediate, direct awareness of something. All our thinking, in one way or another, aims for this direct awareness as its ultimate goal.

However, this intuition only happens if an object is actually given to us. This, in turn, is only possible if the object affects our mind in a certain way. The ability of our mind to receive mental pictures or ideas (representations) when we are affected by objects is called sensibility. Sensibility is like our mind’s capacity to be open and receptive to information from the world.

So, objects are given to us through our sensibility. Sensibility alone provides us with these direct awarenesses, or intuitions. Once we have intuitions, we then think about them using our understanding. It is from our understanding that concepts (general ideas) arise.

But all thinking, whether it’s straightforward or more indirect, must ultimately connect back to intuitions. For us humans, this means all our thoughts must connect back to our sensibility. Why? Because there’s no other way for objects to be given to us.

Sensation and Appearance

When an object affects our ability to form representations, this effect is called sensation. For instance, the warmth you feel from the sun is a sensation. An intuition that is related to an object through sensation is called an empirical intuition. “Empirical” means it’s based on experience. The object of an empirical intuition, before our understanding has fully defined it with concepts, is called an appearance. It’s how the object appears to us.

Matter and Form in Appearances

In any appearance, we can identify two aspects:

1. Matter: This is the part of the appearance that corresponds to sensation. It’s the raw data from our senses – like the colors, sounds, or textures we experience. Matter is given to us a posteriori, meaning through experience.
2. Form: This is what allows the variety of an appearance (its diverse elements) to be perceived as organized or ordered in certain ways. For example, seeing several items arranged in a particular pattern. The structure or “container” in which sensations are ordered cannot itself be another sensation. So, this form must not come from sensation. Instead, the form of all appearances must already be present in our mind a priori – before any specific experience. Therefore, we can think about this form separately from all sensation.

Pure Intuition: Form Without Sensation

I call any mental representation pure (in the transcendental sense) if it contains nothing that comes from sensation. Following this, the pure form of our sensible intuitions – the underlying structure for how we sense things – must exist in our mind a priori. This pure form is where all the diverse content of appearances gets ordered. This pure form of sensibility itself is also called pure intuition.

Let’s make this clearer with an example: Imagine you have a mental picture of a physical object, like a ball.

• First, mentally remove everything your understanding thinks about it: concepts like “substance,” “force,” “divisibility,” and so on.
• Next, mentally remove everything that belongs to sensation: qualities like “impenetrable,” “hard,” “red,” and so on.

Even after removing all these, something from your original empirical intuition of the ball is still left: its extension (the space it occupies) and its shape. These aspects – extension and form – belong to pure intuition. Pure intuition happens a priori, even without a real object currently present to our senses or any active sensation. It exists as a fundamental way our sensibility is structured in our minds.

Transcendental Aesthetic: The Science of Pure Sensibility

I call the science that studies all the a priori principles of our sensibility the Transcendental Aesthetic. Such a science must exist. It forms the first part of the broader “Transcendental Doctrine of Elements.” It is different from the part that deals with the principles of pure thinking, which is named “Transcendental Logic.”

Outer Sense, Inner Sense, Space, and Time

We have something called outer sense. This is a property of our mind through which we represent objects as being outside of ourselves. Importantly, we represent all of them as existing in space. It is in space that their shape, size, and relationship to one another are determined or can be determined.

We also have an inner sense. Through inner sense, our mind is aware of itself or its own internal state. Inner sense doesn’t give us an intuition of the “soul” itself as an object. However, it does provide a specific form under which we can be aware of our inner state. This means everything related to our inner thoughts and feelings is represented in relationships of time.

Time cannot be perceived externally (as something outside us), just as space cannot be perceived as something inside us (like a thought or feeling).

So, what exactly are space and time?

• Are they actual existing things, like physical objects?
• Are they just properties or relations of things that would exist even if we weren’t perceiving them?
• Or, are they relations that only belong to the form of our intuition? This would mean they are part of the subjective makeup of our own minds. Without this mental structure, we couldn’t attribute these properties (like “being in space”) to anything at all.

To understand this, let’s first consider space.

Arguments About Space

1. Space is not learned from experience. Space is not an empirical concept that we get from outer experiences. For me to relate certain sensations to something outside of me (that is, to something in a different place in space from where I am), I must already have a representation of space. For me to see objects as outside one another—not just as different, but as in different places—the idea of space must already be there as a foundation. Therefore, we don’t get the representation of space from observing the relations between outer appearances through experience. Instead, outer experience itself is only possible because we already have this representation of space.

2. Space is a necessary, a priori foundation for perception. Space is a necessary representation that exists a priori (before experience). It is the ground for all our outer intuitions (our direct awareness of external things). You can never imagine that there is no space. However, you can easily think of space as empty, with no objects in it. Therefore, space should be seen as the condition that makes appearances possible, not as some feature that depends on them. It is an a priori representation that necessarily underlies all outer appearances.

3. Space is a pure intuition, not a general concept. Space is not a discursive (or general) concept about how things relate in general. It is a pure intuition. Here’s why: First, you can only represent one single space. When we talk about “many spaces,” we just mean parts of one and the same unique, all-encompassing space. These parts don’t come before the single, whole space as if they were components that could be assembled to make it. Instead, parts are only thought of within the one space. Space is essentially single. The variety within it (and thus the general concept of “spaces”) comes from imposing limitations on this single space. From this, it follows that an a priori intuition (one that is not empirical) is the foundation for all our concepts about space. This is also why all geometrical principles (e.g., in a triangle, any two sides added together are always greater than the third side) are never derived from general concepts like “line” or “triangle.” Instead, they are derived from intuition, and specifically, they are derived a priori with absolute certainty.

Conclusions About Space

From these points about space, we can draw the following conclusions:

a)  **Space is not a property of things in themselves.**
    Space does not represent any property of things as they are in themselves, nor does it represent any relation between them as they are in themselves. It’s not a characteristic that attaches to objects themselves and that would remain even if we were to ignore all the subjective conditions of how we perceive (our intuition). This is because neither absolute properties (like "this thing *is* X") nor relative properties (like "A is next to B") can be intuited *before* the existence of the things they belong to. So, such properties cannot be intuited *a priori*.

b)  **Space is the form of our outer sense.**
    Space is nothing other than the form of all appearances of our outer sense. It is the subjective condition of our sensibility, under which alone outer intuition is possible for us.
    Now, because our capacity to be affected by objects (our receptivity) must necessarily exist *before* any intuitions of these objects, we can understand something crucial: The form of all appearances (space) can be present in our mind *before* any actual perceptions, meaning it's there *a priori*. And as a pure intuition in which all objects must be arranged, it can contain the principles of their relationships *before* we have any experience of them.

The Human Standpoint on Space

Therefore, we can talk about space, extended objects, and so on, only from a human standpoint. If we set aside the subjective condition under which alone we can have outer intuition – namely, our particular way of being affected by objects – then the representation of space means nothing at all. This characteristic (being “in space”) is attributed to things only insofar as they appear to us, meaning they are objects of our sensibility.

The constant form of this receptivity, which we call sensibility, is a necessary condition for all the relationships in which objects can be perceived as outside us. If we mentally subtract these objects, what remains is this pure intuition, which we call space.

We cannot make the special conditions of our sensibility (like space) into conditions for the possibility of things in themselves. We can only make them conditions for the possibility of their appearances to us. So, we can correctly say that space includes all things that may appear to us externally. But we cannot say that space includes all things in themselves, whether they are intuited or not, or by whatever kind of mind they might be intuited. We simply cannot judge whether the intuitions of other thinking beings (if they exist) are bound by the same conditions that limit our intuition and that are universally valid for us.

If we add a limitation to a judgment related to the subject experiencing it, then the judgment becomes unconditionally valid. For example, the statement “All things are next to one another in space” is valid only under the limitation that these things are taken as objects of our sensible intuition. If I refine this and say: “All things, as outer intuitions, are next to one another in space,” then this rule is valid universally and without any further limitation.

Our explanations, therefore, show the reality (meaning, objective validity) of space concerning everything that can come before us externally as an object. But at the same time, they show the ideality of space concerning things when they are considered in themselves by reason (that is, without taking into account the structure of our sensibility). So, we assert the empirical reality of space (it’s real with respect to all possible outer experience). However, we also assert its transcendental ideality (it’s nothing as soon as we leave out the condition of the possibility of all experience – our sensibility – and consider space as something that grounds things in themselves).

Besides space, however, there is no other subjective representation related to something external that could be called a priori objective.

The Purpose of Clarifying Space’s Ideality

The aim of this remark is only to prevent anyone from thinking of illustrating the asserted ideality of space with completely inadequate examples. Things like colors, taste, etc., are correctly considered not as qualities of things but as mere alterations of our subject, which can even be different in different people. For in this case, that which is originally itself only appearance (e.g., a rose) counts in an empirical sense as a thing in itself, which yet can appear different to every eye in regard to color. The transcendental concept of appearances in space, on the contrary, is a critical reminder that absolutely nothing that is intuited in space is a thing in itself. Space is not a form that is proper to anything in itself. Rather, objects in themselves are not known to us at all. What we call outer objects are nothing other than mere representations of our sensibility, whose form is space. But their true correlate—that is, the thing in itself—is not and cannot be known through them, nor is it ever asked after in experience.

The Transcendental Aesthetic: Second Section – On Time

Now, let’s consider time.

1. Time is not learned from experience. Time is not an empirical concept that is somehow drawn from experience. For simultaneity (things happening at the same time) or succession (things happening one after another) would not themselves come into perception if the representation of time did not ground them a priori. Only under its presupposition can one represent that several things exist at one and the same time or in different times.

2. Time is a necessary, a priori foundation for all intuitions. Time is a necessary representation that grounds all intuitions. In regard to appearances in general, one cannot remove time, though one can very well take the appearances away from time (imagine time passing with nothing happening). Time is therefore given a priori. In it alone is all actuality of appearances possible. The latter could all disappear, but time itself (as the universal condition of their possibility) cannot be removed.

3. The a priori necessity of time grounds principles about time. This a priori necessity also grounds the possibility of absolutely certain principles of the relations of time, or axioms of time in general. Time has only one dimension: different times are not simultaneous, but successive (just as different spaces are not successive, but simultaneous). These principles could not be drawn from experience, for this would yield neither strict universality nor absolute certainty. We would only be able to say: “This is what common perception teaches,” but not: “This is how matters must stand.” These principles are valid as rules under which alone experiences are possible at all, and instruct us before them, not through them.

4. Time is a pure form of sensible intuition, not a general concept. Time is no discursive or, as one calls it, general concept, but a pure form of sensible intuition. Different times are only parts of one and the same time. That representation, however, which can only be given through a single object (or framework), is an intuition. Further, the proposition that different times cannot be simultaneous cannot be derived from a general concept. The proposition is synthetic (it adds new information) and cannot arise from concepts alone. It is therefore immediately contained in the intuition and representation of time.

5. The infinitude of time means it’s a single, grounding framework. The infinitude of time signifies nothing more than that every determinate magnitude of time (like an hour or a day) is only possible through limitations of a single time grounding it. The original representation, time, must therefore be given as unlimited. But where the parts themselves and every magnitude of an object can be determinately represented only through limitation, there the entire representation cannot be given through concepts (for then the partial representations would come first). Instead, their immediate intuition must be the ground.

Conclusions About Time

From these concepts, we can draw the following conclusions:

a)  **Time is not something that exists by itself or as an objective property of things.**
    Time is not something that would exist on its own, nor does it attach to things as an objective determination that would remain if one abstracted from all subjective conditions of our intuition of them.
    If time were something existing on its own (the first case), it would be something that was actual yet without any actual object filling it.
    As for the second case (time as an objective property of things), time could not precede the objects as a determination or order attaching to the things themselves as their condition and be known and directly perceived *a priori* through propositions that expand our knowledge.
    But the latter (being known *a priori*) *can* very well occur if time is nothing other than the **subjective condition** under which all intuitions can take place *in us*. For then this form of inner intuition (time) can be represented *before* we experience objects, and therefore *a priori*.

b)  **Time is the form of our inner sense.**
    Time is nothing other than the form of our **inner sense**. This means it's the structure of how we are aware of ourselves and our own inner state (our thoughts, feelings, etc.).
    Time cannot be a characteristic of outer appearances; it belongs neither to a shape or a position in space. Instead, time determines the relationship between representations *within our inner state*.
    And precisely because this inner awareness (our inner intuition) doesn't provide us with any shape, we also attempt to make up for this lack through analogies. We often represent the sequence of time as a line progressing infinitely. On this line, the variety of moments forms a series that has only one dimension (length). We then infer all the properties of time from the properties of this line, with the sole difference that the parts of the line exist all at once (simultaneously), but the parts of time always exist one after another (successively).
    From this, it is also apparent that the representation of time is itself an **intuition** (a direct awareness), since all its relations can be expressed in an outer intuition (like the line).

c)  **Time is the *a priori* formal condition for all appearances in general.**
    Space, as the pure form of all *outer* intuitions, is limited as an *a priori* condition merely to those outer intuitions.
    However, *all* our representations – whether they have outer things as their object or not – belong to our inner state because they are, after all, determinations of our mind. This inner state, in turn, falls under the formal condition of inner intuition, which is **time**.
    Therefore, time is an *a priori* condition for *all appearance in general*. It is the immediate condition for inner appearances (of our souls or minds). And because outer appearances eventually become representations in our inner state, time is also the indirect (mediate) condition for outer appearances.
    So, if I can say *a priori* that "all outer appearances are in space and are determined *a priori* according to the relations of space," then, based on the principle of inner sense, I can say more broadly: "all appearances in general (i.e., all objects of the senses) are in time, and necessarily exist in relations of time."

Time is Real for Experience, but Ideal Apart from Us

If we abstract from our way of internally intuiting ourselves – and by means of this intuition also dealing with all outer intuitions in our capacity for representation – and thus take objects as they may be in themselves, then time is nothing. It only has objective validity in regard to appearances, because these are already things that we take as objects of our senses. But it is no longer objective if one abstracts from the sensibility of our intuition (that is, from that kind of representation that is peculiar to us) and speaks of “things in general.” Time is therefore merely a subjective condition of our (human) intuition (which is always sensible; that is, insofar as we are affected by objects). In itself, outside the subject (us), time is nothing. Nonetheless, it is necessarily objective in regard to all appearances, and thus also in regard to all things that can come before us in experience.

We cannot say that “all things are in time.” This is because when we use the concept of “things in general,” we are removing any specific way we might sense or intuit them. But it’s precisely our way of intuiting that makes time relevant to how we represent objects. Now, if we add this condition to our concept and say, “all things as appearances (as objects of our sensible intuition) are in time,” then this principle has solid objective correctness and a priori universality (it’s true before experience and applies universally to all such objects).

Our statements, therefore, teach the empirical reality of time. This means time has objective validity concerning all objects that may ever be given to our senses. And since our intuition is always sensible (related to our senses), no object can ever be given to us in experience that would not fall under the condition of time. But, on the other hand, we reject any claim that time has absolute reality. We deny that it would attach to things absolutely, as a condition or property, even without considering the form of our sensible intuition. Such properties, which would belong to things as they are in themselves, can never be given to us through the senses.

This, therefore, is what we mean by the transcendental ideality of time. According to this idea, if one ignores the subjective conditions of sensible intuition, time is nothing at all. It cannot be counted as either existing on its own (subsisting) or as a property within objects themselves (inhering), separate from their relation to our intuition. Yet, this ideality of time should not be compared to misperceptions of sensation (like thinking the greenness of a leaf is in the leaf itself apart from our seeing it), just as the ideality of space shouldn’t be. In those cases of misperception, one assumes that the appearance itself (like the green leaf) has objective reality as a thing in itself. This kind of objective reality is entirely absent here when we speak of time transcendentally, except insofar as it is merely empirical. That is, the object itself is regarded merely as an appearance. (You can refer to the remark in the previous sections for more on this.)

Further Explanation (Elucidation) on Time

Some insightful people have unanimously raised an objection against this theory. Our theory grants empirical reality to time but disputes its absolute and transcendental reality. I conclude that this objection must naturally occur to every reader who is not used to these kinds of considerations.

The objection goes like this: “Changes are real. (This is proven by the change of our own mental representations, even if one were to deny all outer appearances and their changes.) Now, changes are possible only in time. Therefore, time is something real.”

There is no difficulty in answering this. I admit the entire argument. Time is certainly something real; namely, it is the real form of inner intuition. It therefore has subjective reality with regard to inner experience. That is, I really do have the representation of time and of my own states (my determinations) within it. Therefore, time should be regarded not as an object itself, but as the way of representing myself as an object.

But if I, or any other being, could be aware of myself without this condition of sensibility (time), then these very same states, which we now represent to ourselves as changes, would give us a kind of knowledge in which the representation of time, and therefore also of change, would not occur at all. So, its empirical reality remains as a condition of all our experiences. Only absolute reality cannot be granted to it, based on what we’ve discussed. Time is nothing except the form of our inner intuition. If one removes the special condition of our sensibility from it, then the concept of time also disappears. It does not stick to the objects themselves, but only to the subject that intuits them.

Why This Objection About Time is Common

The reason this objection about time’s reality is made so unanimously, even by those who don’t have convincing arguments against the ideality of space, is this: They didn’t expect to be able to prove the absolute reality of space with complete certainty because they were faced with idealism. Idealism suggests that the reality of outer objects cannot be strictly proven. On the contrary, the reality of the object of our inner sense (of myself and my state) seems immediately clear through consciousness. Outer objects could be mere illusions, but our inner state, in their opinion, is undeniably something real.

However, they didn’t consider that both inner and outer states, while their reality as representations isn’t disputed, still belong only to appearance. Appearance always has two sides:

1. One side where the object is considered in itself (without regard to the way it is intuited; the nature of this object in itself must therefore always remain problematic and unknown).
2. The other side where the form of the intuition of this object is considered. This form must not be sought in the object in itself, but in the subject to whom it appears. Nevertheless, this form really and necessarily pertains to the representation of this object.

Space and Time as Sources of Knowledge

Accordingly, space and time are two sources of knowledge from which different kinds of synthetic knowledge (knowledge that expands our understanding) can be drawn a priori. Pure mathematics provides a splendid example of this, especially concerning knowledge of space and its relations.

Taken together, space and time are the pure forms of all sensible intuition. They thereby make synthetic a priori propositions (statements that are true before experience and expand our knowledge) possible. But these a priori sources of knowledge also determine their own boundaries by the very fact that they are merely conditions of sensibility. Their boundary is that they apply to objects only as far as objects are considered as appearances. They do not present things as they are in themselves. Appearances alone are the field of their validity; beyond this field, no further objective use of them can take place.

This reality of space and time (as forms of our intuition) leaves the certainty of experiential knowledge untouched. We are just as certain of our experiences whether these forms necessarily stick to the things in themselves or only to our intuition of these things.

However, those who assert the absolute reality of space and time (whether they assume space and time exist on their own or are just properties inherent in things) must come into conflict with the principles of experience.

• If they choose the first option (that space and time exist on their own – generally the position of mathematical investigators of nature), then they must assume two eternal and infinite self-subsisting non-entities (space and time). These non-entities supposedly exist (yet without there being anything real in them) only to contain everything real within themselves.
• If they adopt the second position (as some metaphysicians of nature do), and hold that space and time are relations of appearances (next to or successive to one another) that are abstracted from experience (though confusedly represented in this abstraction), then they must dispute the validity, or at least the absolute certainty, of a priori mathematical doctrines concerning real things (e.g., things in space). They must do this because this certainty does not come from experience (a posteriori). On their view, the a priori concepts of space and time are only creations of the imagination. The origin of these concepts would really have to be sought in experience, from whose abstracted relations the imagination has made something that, while containing what is general in them, cannot exist without the restrictions that nature has attached to them.

The first group (mathematical investigators) succeeds in opening the field of appearances for mathematical statements. However, they themselves become very confused by these very conditions (space and time as self-subsisting non-entities) if the understanding tries to go beyond this field of appearances. The second group (metaphysicians of nature) succeeds, with respect to going beyond appearances, in that their representations of space and time do not stand in their way if they want to judge objects not as appearances but merely in relation to the understanding. However, they can neither offer any ground for the possibility of a priori mathematical knowledge (since they lack a true and objectively valid a priori intuition for space and time), nor can they bring the propositions of experience into necessary agreement with those mathematical assertions.

On our theory of the true nature of these two original forms of sensibility (space and time), both these difficulties are resolved.

Why Only Space and Time in Transcendental Aesthetic?

Finally, it is clear that the transcendental aesthetic cannot contain more than these two elements, namely space and time. This is because all other concepts belonging to sensibility – even the concept of motion, which unites both elements – presuppose something empirical. Motion, for instance, presupposes the perception of something movable. In space considered in itself, there is nothing movable. Therefore, the movable must be something that is found in space only through experience; it is an empirical datum. In the same way, the transcendental aesthetic cannot count the concept of alteration among its a priori data. Time itself does not alter; only something that is within time alters. For this, the perception of some existence and the succession of its states (its determinations) is required – in other words, experience.

General Remarks on the Transcendental Aesthetic

First, it will be necessary to explain our opinion about the fundamental nature of sensible knowledge in general as clearly as possible, to prevent any misinterpretation.

We have wanted to say that all our intuition is nothing but the representation of appearance.

• The things that we intuit are not, in themselves, what we intuit them to be.
• Nor are their relations constituted in themselves as they appear to us.
• If we remove our own subject (our mind), or even just the subjective constitution of our senses in general, then all the constitution, all relations of objects in space and time – indeed space and time themselves – would disappear.
• As appearances, they cannot exist in themselves, but only in us.

What may be the case with objects in themselves, abstracted from all this receptivity of our sensibility, remains entirely unknown to us. We are acquainted with nothing except our way of perceiving them. This way is peculiar to us, and therefore does not necessarily pertain to every being, though it certainly pertains to every human being. We are concerned solely with this. Space and time are its pure forms; sensation in general is its matter.

• We can know the pure forms (space and time) a priori, i.e., before any actual perception. They are therefore called pure intuition.
• The matter (sensation), however, is what makes our knowledge a posteriori cognition, i.e., empirical intuition. The pure forms adhere to our sensibility absolutely necessarily, whatever sort of sensations we may have. The sensations themselves can be very different.

Even if we could bring this intuition of ours to the highest degree of distinctness, we would not thereby come any closer to the constitution of objects in themselves. We would, in any case, still only completely know our own way of intuiting, i.e., our sensibility. And this knowledge would always be only under the conditions originally depending on the subject: space and time. What the objects may be in themselves would still never be known through the most enlightened cognition of their appearance, which is all that is ever given to us.

Therefore, the idea that our entire sensibility is nothing but a confused representation of things, which solely contains what pertains to them in themselves but only under a heap of marks and partial representations that we can never consciously separate, is a falsification of the concept of sensibility and of appearance. It renders the entire theory of them useless and empty. The difference between an indistinct and a distinct representation is merely logical; it does not concern the content or origin. Without doubt, the concept of “right” (as in justice) that is used by common sense contains the very same things that the most subtle speculation can develop out of it. It’s just that in common and practical use, one is not conscious of these many underlying representations within these thoughts. Thus, one cannot say that the common concept of right is “sensible” and contains a mere “appearance,” because right cannot appear at all. Rather, its concept lies in the understanding and represents a constitution (the moral constitution) of actions that pertains to them in themselves. The representation of a physical body in intuition, on the contrary, contains nothing at all that could pertain to an object in itself. It merely contains the appearance of something and the way in which we are affected by it. This receptivity of our cognitive capacity is called sensibility, and it remains worlds apart from the cognition of the object in itself, even if one might see through to the very bottom of the appearance.

The Leibnizian-Wolffian philosophy, therefore, directed all investigations of the nature and origin of our cognitions to an entirely incorrect point of view. It did so by considering the distinction between sensibility and the intellectual (or understanding) as merely logical (a matter of clearness or confusion). However, the distinction is obviously transcendental. It does not concern merely the form of distinctness or indistinctness, but its origin and content. So, through sensibility, we do not cognize the constitution of things in themselves merely indistinctly; rather, we do not cognize them at all. As soon as we take away our subjective constitution (our specific way of sensing), the represented object, along with the properties that sensible intuition attributes to it, is nowhere to be found, nor can it be encountered. This is because it is precisely this subjective constitution that determines its form as an appearance.

We ordinarily distinguish quite well between that which is essentially attached to the intuition of appearances and is valid for every human sense in general, and that which pertains to them only contingently (by chance). The contingent kind is not valid for sensibility in general but only for a particular situation or organization of this or that sense. And so, one calls the first kind of cognition one that represents the object in itself, but the second kind only its appearance. This distinction, however, is only empirical.

If one stands by this common distinction (as usually happens) and does not regard that empirical intuition (our everyday perception) as in turn mere appearance (as one ought to), so that there is nothing to be encountered in it that pertains to anything in itself, then our transcendental distinction is lost. We then believe ourselves to be knowing things in themselves, although we have nothing to do with anything except appearances anywhere (in the world of sense), even in the deepest research into its objects. Thus, we would certainly call a rainbow a mere appearance in a sun-shower. But we would call this rain the thing in itself. This is correct, as long as we understand “thing in itself” here in a merely physical sense—as that which in universal experience and all different positions relative to the senses is always determined thus and not otherwise in intuition. But if we consider this empirical object (the rain) in general and, without turning to its agreement with every human sense, ask whether it represents an object in itself (not the raindrops, since these, as appearances, are already empirical objects), then the question of the relation of the representation to the object is transcendental. And not only are these drops mere appearances, but even their round form, indeed even the space through which they fall, are nothing in themselves, but only mere modifications or foundations of our sensible intuition. The transcendental object, however, remains unknown to us.

The Certainty of Our Theory of Sensibility

The second important concern of our transcendental aesthetic is that it not merely earn some favor as a plausible hypothesis. It must be as certain and indubitable as can ever be demanded of a theory that is to serve as an “organon” (a fundamental tool for knowledge). In order to make this certainty fully convincing, we will choose a case in which its validity can become obvious.

Thus, if it were supposed that space and time are in themselves objective, and conditions of the possibility of things in themselves, then it would be shown, first, that there are a large number of a priori (known before experience), absolutely certain (“apodictic”), and knowledge-expanding (“synthetic”) propositions about both, but especially about space. We will therefore investigate space here as our primary example. Since the propositions of geometry are known synthetically, a priori, and with absolute certainty, I ask: Where do you take such propositions from? And on what does our understanding rely in attaining such absolutely necessary and universally valid truths?

There is no other way than through concepts or through intuitions (direct awarenesses). Both of these are given, as such, either a priori or a posteriori (from experience). The latter—namely empirical concepts, together with that on which they are grounded, empirical intuition—cannot yield any synthetic proposition except one that is also merely empirical (i.e., a proposition of experience). Thus, it can never contain necessity and absolute universality of the sort that is nevertheless characteristic of all propositions of geometry.

Let’s continue discussing the first and only remaining way to achieve such knowledge (like the truths of geometry) – namely, through mere concepts or through a priori intuitions (direct awareness that comes before experience).

It is clear that from mere concepts alone, you can only get analytic knowledge, not synthetic knowledge.

• Analytic knowledge only clarifies what is already contained in a concept. For example, saying “a triangle has three sides” just analyzes the concept of a triangle.
• Synthetic knowledge, on the other hand, adds new information that wasn’t in the original concept. Geometric truths are like this; they expand our understanding.

Consider these geometric propositions:

• “With two straight lines, no space at all can be enclosed, so no figure is possible.” Try to derive this conclusion just from the concept of “straight lines” and the concept of “two.”
• Or, take the proposition: “A figure is possible with three straight lines.” Again, try to derive this just from these concepts.

All your effort will be useless. You will find yourself forced to turn to intuition (a direct, immediate awareness), just as geometry always does. So, you give yourself an object in intuition, like imagining or drawing a triangle.

But what kind of intuition is this?

• Is it a pure a priori intuition (one that comes from within your mind, before specific experiences)?
• Or is it an empirical one (based on a particular experience or observation)?

If it were an empirical intuition, then no universally valid, let alone absolutely certain (“apodictic”), proposition could ever come from it. Experience can never provide that kind of absolute necessity and universality.

Therefore, you must present your object (like the triangle) to yourself a priori in intuition, and base your synthetic proposition on this a priori intuition.

This leads to some crucial conclusions:

• If you did not have within you a faculty for intuiting a priori (a built-in way to be directly aware of things like space before any experience);
• If this subjective condition related to the form of your intuition (how you structure what you sense) were not at the same time the universal a priori condition under which alone the object of this (outer) intuition (like a triangle) is itself possible;
• If the object (the triangle, for instance) were something existing entirely in itself, without any relation to you as the perceiving subject; …then how could you say that what necessarily lies in your subjective conditions for constructing a triangle must also necessarily belong to the triangle in itself? You could not add something new (the figure of the triangle) to your concept (of three lines) that must then necessarily be found in the actual object, because this object would be given to you before your act of knowing it, and not through that act.

Therefore, if space (and time as well) were not a mere form of your intuition—a form containing a priori conditions under which alone things can be outer objects for you (and these objects are nothing in themselves without these subjective conditions)—then you could make absolutely no synthetic and a priori statements about outer objects.

It is therefore indubitably certain, and not merely possible or even probable, that space and time, as the necessary conditions of all experience (both outer experience of the world and inner experience of ourselves), are merely subjective conditions of all our intuition. In relation to these subjective conditions, therefore, all objects are mere appearances, and not things given “for themselves” or “as they truly are in themselves.” Furthermore, much can be said a priori that concerns the form of these appearances, but nothing whatsoever can be said about the things in themselves that may ground these appearances.

The Transcendental Doctrine of Elements Second Part The Transcendental Logic[A 50/B 74]

We are now beginning the Second Part of the Transcendental Doctrine of Elements, which is called The Transcendental Logic. This introduction will explain the idea behind it.

I. On Logic in General

Our knowledge comes from two fundamental sources in our minds:

1. The first is our ability to receive representations (the mind’s openness to impressions). This is how an object is given to us.
2. The second is our faculty for knowing an object through these representations (the mind’s active ability to form concepts). This is how an object is thought in relation to that representation (as a mental state).

Therefore, intuition (direct awareness) and concepts (general ideas) are the basic building blocks of all our knowledge. Neither concepts without some corresponding intuition, nor intuition without concepts, can produce knowledge.

Both intuitions and concepts can be either pure or empirical:

• They are empirical if sensation is involved (which assumes the actual presence of the object). For example, seeing a specific red apple involves sensation.
• They are pure if no sensation is mixed into the representation. Sensation can be called the matter (the raw material) of sensible knowledge.
  • Thus, pure intuition contains only the form under which something is directly perceived (like space and time).
  • And a pure concept contains only the form of thinking about an object in general.

Only pure intuitions or pure concepts can exist a priori (before or independent of any specific experience). Empirical ones are only possible a posteriori (after or dependent on experience).

Let’s re-emphasize these terms:

• If we call our mind’s capacity to receive representations (when it’s affected in some way) sensibility, then…
• The faculty for producing representations itself, or the spontaneity of knowledge (our mind’s active power), is the understanding.

It is part of our nature that our intuition can only ever be sensible. This means it only involves the way we are affected by objects. On the other hand, the faculty for thinking about the objects given by sensible intuition is the understanding.

Neither of these abilities is better than the other.

• Without sensibility, no object would be given to us.
• Without understanding, no object would be thought.

Thoughts without content are empty; intuitions without concepts are blind. It is therefore just as necessary to make our mind’s concepts sensible (that is, to add an object to them in intuition) as it is to make its intuitions understandable (that is, to bring them under concepts).

Furthermore, these two faculties or capacities cannot switch their functions:

• The understanding is not capable of directly perceiving or intuiting anything.
• The senses are not capable of thinking anything.

Knowledge can only arise from their unification. Because of this, we must not mix up their roles. Instead, we have good reason to carefully separate them from each other and distinguish them. Hence, we distinguish:

• The science of the rules of sensibility in general, which is Aesthetic (as discussed in the First Part).
• The science of the rules of understanding in general, which is Logic.

Divisions Within Logic

Logic, in turn, can be approached with two different aims:

1. Logic of the General Use of Understanding: This contains the absolutely necessary rules of thinking, without which no use of the understanding can happen. It concerns these rules without regard to the different kinds of objects it might be directed to. This can be called elementary logic.
2. Logic of the Particular Use of Understanding: This contains the rules for correctly thinking about a specific kind of object. This is sometimes called the organon (or instrument) of a particular science. Schools often teach this as an introduction to sciences, though in the development of human reason, these specific logics are usually figured out much later, after the science itself is already well-established and just needs final touches. To create rules for how a science of certain objects should be formed, one must already know those objects quite well.

General Logic: Pure vs. Applied

Now, general logic can be either pure logic or applied logic:

• Pure General Logic: In this, we ignore all empirical conditions under which our understanding operates. For example, we ignore the influence of the senses, the play of imagination, the laws of memory, the power of habit, personal inclinations, and so on. We also ignore the sources of prejudice and, in general, all causes from which certain knowledge might arise or be supposed to arise, because these things only concern the understanding under specific circumstances of its application, and experience is needed to know these circumstances. A general but pure logic, therefore, deals with strictly a priori principles. It is a canon of the understanding and reason – meaning it provides the standard or rule, but only for the formal aspect of their use, whatever the content (empirical or transcendental) may be.

• Applied General Logic: This is general logic directed towards the rules of using the understanding under the subjective empirical conditions that psychology teaches us. It therefore has empirical principles, even though it’s “general” because it concerns the use of the understanding without focusing on specific types of objects. Because of this, it is neither a canon of the understanding in general nor an organon (instrument) for particular sciences. It is merely a cathartic (a cleanser or purifier) of the common understanding.

Pure General Logic as a Science

In general logic, the part that is to form the pure teaching of reason must be entirely separated from the part that forms applied (though still general) logic. The former (pure general logic) alone is properly a science, although it is brief and dry, as a scholastically correct presentation of a doctrine of the elements of the understanding requires. In this, logicians must always keep two rules in view:

1. As general logic, it abstracts from all content of the understanding’s knowledge and from the differences between its objects. It deals with nothing but the mere form of thinking.
2. As pure logic, it has no empirical principles. Thus, it draws nothing from psychology (as some have occasionally been persuaded to think). Psychology, therefore, has no influence at all on the canon of the understanding. Pure logic is a proven doctrine, and everything in it must be completely a priori.

What I call applied logic (which is different from the common meaning of the word, where it might mean exercises for which pure logic provides the rules) is a description of the understanding and the rules for its necessary use in specific situations (in concreto). This means it considers the contingent (changeable) conditions of the person using their understanding, conditions which can hinder or help this use, and which can all only be given empirically. It deals with things like:

• Attention, its obstacles, and its results.
• The cause of errors.
• The state of doubt, of holding back judgment, of conviction, etc.

General and pure logic is related to this applied logic in the same way that pure morality (which contains only the necessary moral laws of a free will in general) is related to the actual doctrine of virtue. The doctrine of virtue assesses these moral laws under the hindrances of feelings, inclinations, and passions to which human beings are more or less subject. Such a doctrine of virtue can never yield a true and proven science, because it requires empirical and psychological principles, just as applied logic does.

II. On Transcendental Logic

General logic, as we have shown, abstracts from all content of knowledge. That is, it ignores any relation of knowledge to its object and considers only the logical form in the relation of different pieces of knowledge to one another – the form of thinking in general.

But, as the Transcendental Aesthetic proved, there are pure intuitions as well as empirical intuitions. So, it’s possible that a distinction between pure and empirical thinking of objects could also be found. If this is the case, there would be a kind of logic that does not abstract from all content of knowledge. A logic that contained merely the rules for the pure thinking of an object would exclude all knowledge that had empirical content. It would therefore concern the origin of our knowledge of objects, specifically when that origin cannot be attributed to the objects themselves. General logic, by contrast, has nothing to do with this origin of knowledge. It considers representations (whether they are originally given a priori in ourselves or only empirically) merely with respect to the laws according to which the understanding brings them into relation with one another when it thinks. Therefore, general logic deals only with the form of the understanding, which can be applied to representations wherever they may have originated.

An Important Remark on “Transcendental”

And here I make a remark that is important for all following discussions, and that we must keep clearly in view: Not every a priori knowledge should be called transcendental. Only that knowledge is transcendental by means of which we know that certain representations (intuitions or concepts) are applied entirely a priori, or how they are possible a priori. This refers to the possibility of such knowledge or its a priori use.

Therefore:

• Neither space itself, nor any a priori geometrical determination of it, is a transcendental representation.
• However, the knowledge that these representations (like space) are not of empirical origin at all, AND the possibility that they can nevertheless be related a priori to objects of experience – this knowledge can be called transcendental.
• Likewise, the use of space for all objects in general would also be transcendental. But if its use is restricted solely to objects of the senses, then it is called empirical.

The difference between the transcendental and the empirical, therefore, belongs only to the critique of knowledge itself (how we examine and understand knowledge) and does not concern the relation of our knowledge to its object.

The Idea of Transcendental Logic

So, in the expectation that there can perhaps be concepts that may be related to objects a priori – not as pure or sensible intuitions, but rather merely as acts of pure thinking (thus, concepts that are of neither empirical nor aesthetic origin) – we provisionally formulate the idea of a science of pure understanding and of pure rational knowledge. By means of this science, we would think objects completely a priori. Such a science, which would determine the origin, the scope, and the objective validity of such knowledge, would have to be called Transcendental Logic. It has to do merely with the laws of the understanding and reason, but only insofar as they are related to objects a priori. This is different from general logic, which deals with empirical as well as pure cognitions of reason without making this distinction about their a priori relation to objects.

III. On the Division of General Logic into Analytic and Dialectic

There’s an old and famous question with which logicians were supposedly driven into a corner. It forced them either to argue in a miserable circle or else confess their ignorance and thus the uselessness of their entire art. The question is this: What is truth?

The common definition of truth – namely, that it is the agreement of knowledge with its object – is granted and presupposed here. But what people demand to know is the general and certain criterion of the truth of any knowledge.

It is already a great and necessary proof of cleverness or insight to know what one should reasonably ask. For if the question is absurd in itself and demands unnecessary answers, then, besides embarrassing the person who proposes it, it also has the disadvantage of misleading the unwary listener into absurd answers. This presents the ridiculous sight (as the ancients said) of one person milking a male goat while another holds a sieve underneath.

If truth consists in the agreement of a piece of knowledge with its object, then this object must thereby be distinguished from others. For a piece of knowledge is false if it does not agree with the specific object to which it is related, even if it contains something that could well be valid for other objects. Now, a general criterion of truth would be one that was valid for all knowledge, without any distinction between their objects. But it is clear that with such a criterion, one abstracts from all content of knowledge (its relation to its object). Yet truth precisely concerns this content. Therefore, it would be completely impossible and absurd to ask for a mark of the truth of this content of knowledge. Thus, it is clear that a sufficient and yet at the same time general sign of truth cannot possibly be provided. Since we have called the content of knowledge its matter, one must say that no general sign of the truth of the matter of knowledge can be demanded, because that is self-contradictory.

However, concerning the mere form of knowledge (setting aside all content), it is equally clear that a logic, so far as it explains the general and necessary rules of understanding, must present criteria of truth in these very rules. For whatever contradicts these rules is false, since the understanding thereby contradicts its general rules of thinking and thus contradicts itself. But these criteria concern only the form of truth (i.e., of thinking in general). To that extent, they are entirely correct but not sufficient. For although a piece of knowledge may be in complete accord with logical form (i.e., not contradict itself), it can still always contradict the object. The merely logical criterion of truth – namely, the agreement of a piece of knowledge with the general and formal laws of understanding and reason – is therefore certainly the conditio sine qua non (the indispensable condition) and thus the negative condition of all truth. Logic, however, cannot go further than this. An error that concerns not form but content cannot be discovered by any test of logic.

General Logic as Analytic and Dialectic

General logic analyzes the entire formal business of the understanding and reason into its elements. It presents these elements as principles for all logical assessment of our knowledge. This part of logic can therefore be called an Analytic. Precisely because of this, it is at least the negative touchstone of truth: one must first of all examine and evaluate the form of all knowledge by means of these rules before investigating its content to find out whether it contains positive truth with regard to the object.

But since the mere form of knowledge, however well it may agree with logical laws, is far from enough to establish the material (objective) truth of the knowledge, nobody can dare to judge objects or assert anything about them merely with logic. One must first draw on well-founded information about them from outside of logic. Only then can one investigate its use and connection in a coherent whole according to logical laws, or, better, solely examine them according to such laws.

Nevertheless, there is something so seductive in possessing an apparent art for giving all our knowledge the form of understanding – even though one may yet be very empty and poor with regard to its content. Because of this, this general logic, which is merely a canon for judging, has been used as if it were an organon (an instrument) for the actual production of at least the semblance of objective assertions. And thus, in fact, it has thereby been misused. Now, general logic, when it is mistakenly used as an organon, is called Dialectic.

However different the meaning of this term “dialectic” (for a science or art) may have been among the ancients, one can still infer from their actual use of it that for them it was nothing other than the logic of illusion. It was a sophistical art for giving ignorance, indeed even intentional tricks, the appearance of truth. It did this by imitating the method of thoroughness that logic generally prescribes, and using logic’s topics for the embellishment of every empty pretension.

Now, one can take it as a certain and useful warning that general logic, considered as an organon, is always a logic of illusion; that is, it is dialectical. For since it teaches us nothing at all about the content of knowledge, but only the formal conditions of agreement with the understanding (which are entirely indifferent with regard to the objects), the audacity of using it as a tool (organon) for an expansion and extension of one’s information, or at least the pretense of doing so, comes down to nothing but idle chatter. One can assert or challenge whatever one wants with some plausibility.

Such instruction by no means befits the dignity of philosophy. For this reason, it would be better to take this designation of “Dialectic” as a critique of dialectical illusion. This critique is counted as part of logic, and that is how we intend it to be understood here.

IV. On the Division of Transcendental Logic into the Transcendental Analytic and Dialectic

In a transcendental logic, we isolate the understanding (just as we isolated sensibility in the Transcendental Aesthetic). We lift out from our knowledge merely that part of our thought that has its origin solely in the understanding. The use of this pure knowledge, however, depends on this as its condition: that objects are given to us in intuition, to which this pure knowledge can be applied. For without intuition, all our knowledge would lack objects and therefore remain completely empty.

The part of transcendental logic, therefore, that explains the elements of the pure knowledge of the understanding, and the principles without which no object can be thought at all, is the Transcendental Analytic. At the same time, this is a logic of truth.

This Transcendental Analytic is a logic of truth because no knowledge can contradict it without, at the same time, losing all its content. If knowledge loses its content, it loses all relation to any object, and therefore, it loses all truth.

However, it is very tempting and seductive to use these pure cognitions (knowledge bits) of the understanding and its principles all by themselves. People are tempted to use them even beyond the limits of experience. But experience alone is what gives us the “matter” – the actual objects – to which those pure concepts of the understanding can be applied.

When the understanding tries to go beyond experience in this way, it falls into the danger of making a “material use” of what are merely “formal principles” of pure understanding. This means it tries to make claims about the actual content or substance of things using only the rules about the structure of thought. This leads to empty, misleading arguments (sophistries) and judging, without proper grounds, about objects that are not given to us – objects which perhaps could not be given to us in any way.

The Transcendental Analytic should properly be only a canon: a set of rules for assessing how we use our understanding empirically (in relation to experience). It is misused if one lets it count as an organon: an instrument for generating knowledge in a general and unrestricted way, daring to synthetically judge, assert, and decide about objects in general using only the pure understanding. The use of the pure understanding in this overreaching way would therefore be dialectical (leading to illusions or deceptive reasoning).

The second part of transcendental logic must therefore be a critique of this dialectical illusion. This part is called Transcendental Dialectic.

• It is not an art of dogmatically (authoritatively and without proof) creating such illusions – an art which, unfortunately, is very common in the many works of “metaphysical jugglery” (clever but deceptive philosophical arguments).
• Rather, Transcendental Dialectic is a critique of the understanding and reason concerning their “hyperphysical” use (their attempt to operate beyond the physical, experiential world).
• Its purpose is to uncover the false illusion of their groundless pretensions (their unjustified claims to knowledge).
• It aims to reduce their claims to invention and expansion of knowledge – supposedly achieved through transcendental principles – to what they really are: a matter for the mere assessment and evaluation of the pure understanding.
• By doing this, it guards the pure understanding against sophistical tricks (clever but false arguments).

Transcendental Logic First Division[B89]

Transcendental Logic: First Division The Transcendental Analytic

This part, the Transcendental Analytic, is like a detailed breakdown of all our knowledge that we have before experience (a priori knowledge). It breaks this knowledge down into the basic elements that come purely from our understanding.

The Transcendental Analytic focuses on several key points about these basic elements, which are concepts:

1. Purity: The concepts must be pure concepts, not empirical ones (concepts learned from experience).
2. Origin: They must belong to thinking and understanding, not to intuition (direct awareness) or sensibility (our capacity to sense).
3. Simplicity: They must be elementary concepts – the most basic building blocks – and clearly different from concepts that are derived from or made up of these basic ones.
4. Completeness: The list or system of these concepts must be complete. It must cover the entire field of the pure understanding without leaving anything out.

Now, achieving such completeness in a science isn’t something we can reliably do just by making a rough guess or by collecting ideas haphazardly. True completeness is possible only if we have an idea of the whole of the understanding’s a priori knowledge. This overall idea helps us determine how to divide and organize the concepts, forming a connected system.

The pure understanding separates itself completely not only from everything empirical but even from all sensibility. Therefore, it is a unity that stands on its own. It is sufficient by itself and does not need any additions from outside. Because of this, the total sum of the pure understanding’s knowledge will form a system. This system is understood and structured under one guiding idea. The completeness and clear organization of this system can then serve as a standard or test to check the correctness and genuineness of all the individual pieces of knowledge that fit into it.

This whole part of transcendental logic, the Transcendental Analytic, consists of two books:

• The first book contains the concepts of pure understanding.
• The second book contains its principles (the fundamental rules or truths based on these concepts).

Transcendental Logic Second Part Transcendental Dialectic[A293/B249]

Transcendental Logic Second Part: Transcendental Dialectic

Introduction

I. Transcendental Illusion

Earlier, we described dialectic in general as a “logic of illusion.” This doesn’t mean it’s a theory about probability. Probability deals with truth that is known through insufficient grounds, so while the knowledge might be flawed, it’s not necessarily deceptive. Therefore, probability doesn’t need to be separated from the analytical (truth-seeking) part of logic. Even less should we confuse appearance with illusion.

Truth and illusion are not found in the object itself as we directly perceive it (intuit it). Instead, they are found in the judgment we make about the object when we think about it. So, it’s correctly said that our senses do not make mistakes. This isn’t because they always judge correctly, but because they do not judge at all. Therefore, truth, as well as error – and also illusion, which leads to error – are found only in judgments. That is, they are found only in the relationship between the object and our understanding.

In knowledge that completely agrees with the laws of the understanding, there is no error. In a representation from our senses (like a raw sight or sound), there is no error because it contains no judgment at all. No force of nature can, on its own, depart from its own laws. Therefore:

• The understanding by itself (without the influence of another cause) cannot make a mistake. This is because when it acts merely according to its own laws, its effect (the judgment) must necessarily agree with these laws. The formal aspect of all truth consists in this agreement with the laws of the understanding.
• The senses by themselves cannot make a mistake, as they make no judgments, neither true nor false.

Since we have no other sources of knowledge besides these two (sensibility and understanding), it follows that error is caused only by the unnoticed influence of sensibility on the understanding. This influence causes the subjective reasons for our judgment to mix with the objective ones, making our judgments deviate from their proper course. Imagine a moving body: by itself, it would always continue in a straight line in the same direction. But it starts to move in a curved line if, at the same time, another force influences it in a different direction. To distinguish the proper action of the understanding from the force that interferes with it, it will be necessary to view an incorrect judgment as a kind of diagonal line resulting from two forces. These two forces pull the judgment in two different directions, forming an angle, so to speak. We then need to break down this combined effect into the simple effects of the understanding and of sensibility. In pure a priori judgments (judgments made before experience), this must happen through transcendental reflection. As we’ve already shown, transcendental reflection assigns every representation to its proper place in our cognitive faculty, and therefore also distinguishes the influence of that faculty on the representation.

Our main concern here is not with empirical illusion (like optical illusions). Empirical illusion occurs in the everyday use of otherwise correct rules of the understanding, where our judgment is misled by the influence of imagination. Instead, we are dealing only with transcendental illusion. This kind of illusion influences principles whose use is never meant for experience. If their use were meant for experience, we would at least have a way to test their correctness. But transcendental illusion, against all warnings of critical thinking, carries us away beyond the empirical use of our conceptual categories. It holds out to us the false appearance of extending the pure understanding beyond its proper limits.

We will call principles whose application stays entirely within the limits of possible experience immanent principles. Those principles that would try to fly beyond these boundaries, we will call transcendent principles. By “transcendent principles,” I don’t mean the transcendental use or misuse of categories. That is just a mistake of judgment when it’s not properly checked by critical thinking and doesn’t pay enough attention to the boundaries of the territory where the pure understanding is allowed to operate. Instead, I mean principles that actually encourage us to tear down all those boundary posts and to lay claim to a wholly new territory that recognizes no demarcations anywhere. Hence, transcendental and transcendent are not the same. The principles of pure understanding we presented earlier should only be used empirically (within experience), not transcendentally (in a way that reaches beyond the boundaries of experience). A principle that removes these limits, or indeed encourages us to overstep them, is called transcendent. If our critical examination can succeed in discovering the illusion in these supposed transcendent principles, then those principles that are of merely empirical use can be called, in contrast to them, immanent principles of pure understanding.

Logical illusion, which consists in merely imitating the form of reason (like the illusion of a misleading argument), arises solely from a failure to pay attention to the logical rule. As soon as this attention is focused on the specific case, logical illusion entirely disappears. Transcendental illusion, on the other hand, does not cease even when it is uncovered and its falsity is clearly seen through transcendental criticism. An example is the illusion in the statement: “The world must have a beginning in time.” The cause of this persistent illusion is that in our reason (considered subjectively as a human faculty of knowledge) there are fundamental rules and maxims for its use. These rules look entirely like objective principles. Because of them, the subjective necessity of a certain connection of our concepts (which is for the benefit of the understanding) is mistaken for an objective necessity (a determination of things in themselves). This is an illusion that cannot be avoided at all. It’s like how we cannot avoid the sea appearing higher in the middle than at the shores (because we see the middle part through higher rays of light than the shores). Or, even better, it’s like how an astronomer cannot prevent the rising moon from appearing larger to him, even when he is not deceived by this illusion in his judgments.

The Transcendental Dialectic will therefore content itself with uncovering the illusion in transcendental judgments, while at the same time protecting us from being deceived by it. However, it can never make transcendental illusion itself disappear and cease to be an illusion (unlike logical illusion). What we are dealing with here is a natural and unavoidable illusion. It rests on subjective principles and passes them off as objective. Logical dialectic, when it dissolves misleading arguments, deals only with an error in following principles or with an artificial illusion that imitates them. Hence, there is a natural and unavoidable dialectic of pure reason. It’s not one in which a clumsy thinker might get entangled through lack of knowledge, or one that some sophist has artfully invented to confuse rational people. Instead, it is one that is incurably attached to human reason. So, even after we have exposed the mirage, it will still not cease to lead our reason on with false hopes, continually propelling it into momentary errors that always need to be removed.

II. On Pure Reason as the Seat of Transcendental Illusion

A. On Reason in General

All our knowledge starts from the senses, goes from there to the understanding, and ends with reason. Beyond reason, there is nothing higher to be found in us to work on the material of intuition and bring it under the highest unity of thinking. Since I am now to give a definition of this supreme faculty of knowledge (reason), I find myself in some difficulty. Just like the understanding, reason has:

1. A merely formal use (which is logical): Here, reason abstracts from all content of knowledge.
2. A real use: Here, reason itself contains the origin of certain concepts and principles, which it derives neither from the senses nor from the understanding.

Logicians have long defined the first faculty (formal/logical use of reason) as that of drawing inferences indirectly (mediately), as distinct from drawing immediate inferences. But this definition gives us no insight into the second faculty, the one that itself generates concepts. Now, since a division of reason into a logical faculty and a transcendental faculty occurs here, we must seek a higher concept for this source of knowledge that includes both these aspects. From our experience with the concepts of the understanding, we can expect two things:

• That the logical concept of reason will give us the key to understanding the transcendental one.
• That the table of functions of the logical use of reason will give us the “family tree” of the concepts of reason.

In the first part of our transcendental logic, we defined the understanding as the faculty of rules. Here, we will distinguish reason from understanding by calling reason the faculty of principles.

The term “a principle” is ambiguous. It commonly means only a piece of knowledge that can be used as a principle, even if in itself and by its own origin it is not a principle. Every universal statement, even if it is taken from experience (by induction), can serve as the major premise in a logical argument (a syllogism); but it is not therefore itself a principle in the stricter sense. Mathematical axioms (e.g., that there can be only one straight line between any two points) are even universal a priori knowledge, and so they are correctly called principles relative to the specific cases that can be included under them. But I cannot therefore say that in general and in itself I know this proposition about straight lines from principles; I only know it in pure intuition.

I would therefore call “knowledge from principles” that knowledge in which I recognize the particular in the universal through concepts. Thus, every syllogism is a way of deriving knowledge from a principle. For the major premise always gives a concept such that everything included under its condition can be known from it according to a principle. Now, since every universal piece of knowledge can serve as the major premise in a syllogism, and since the understanding provides such universal a priori propositions, these propositions can, with respect to their possible use, be called principles.

But if we consider these principles of pure understanding in themselves, looking at their origin, then they are anything but knowledge derived from concepts. They would not even be possible a priori if we did not bring in pure intuition (as in mathematics) or the conditions of a possible experience in general. The statement “everything that happens has a cause” cannot be inferred at all from the concept of “what happens in general.” Rather, it is this very principle that shows how one can first get a definite experiential concept of “what happens.”

Thus, the understanding cannot produce synthetic knowledge (knowledge that expands our understanding) from concepts at all. It is properly these kinds of synthetic knowledge derived from concepts that I call principles absolutely. Nevertheless, all universal propositions in general can be called principles in a comparative sense.

It is an ancient wish – who knows how long it will take until perhaps it is fulfilled – that instead of the endless variety of civil laws, their principles might be sought out. For in this alone, it is said, can consist the secret of simplifying legislation. But in the case of laws, they are only limitations of our freedom to conditions under which it thoroughly agrees with itself. Hence, laws apply to something that is wholly our own work, and of which we can be the cause through that concept. But the idea that objects in themselves, as well as the nature of things, should stand under principles and be determined according to mere concepts is something that, if not impossible, is at least very paradoxical in what it demands. However that may be (for the investigation of this still lies before us), this much at least is clear: knowledge from principles (in themselves) is something entirely different from mere knowledge of the understanding. The understanding’s knowledge can, of course, come before other knowledge in the form of a principle, but in itself (insofar as it is synthetic) it still neither rests on mere thought nor contains in itself a universal truth according to concepts.

If the understanding can be called a faculty for creating unity in appearances by means of rules, then reason is the faculty for creating unity in the rules of understanding by means of principles. Thus, reason never applies directly to experience or to any object. Instead, it applies to the understanding, in order to give an a priori unity through concepts to the understanding’s diverse knowledge. This unity may be called “the unity of reason,” and it is of an altogether different kind than any unity that can be achieved by the understanding.

This is the universal concept of the faculty of reason, as far as that concept can be made understandable without specific examples (which will be given later).

B. On the Logical Use of Reason

We draw a distinction between what is known immediately and what is only inferred.

• That there are three angles in a figure enclosed by three straight lines is known immediately.
• But that these angles together equal two right angles is only inferred.

Because we constantly need to make inferences, we eventually become so accustomed to them that we no longer even notice this distinction. Often, as in so-called deceptions of the senses, we take something as immediately perceived when we have actually only inferred it.

In every inference, there is:

1. A proposition that serves as a ground (a reason or basis).
2. Another proposition, the conclusion, that is drawn from the first.
3. Finally, the inference itself (the logical consequence) according to which the truth of the conclusion is unfailingly connected with the truth of the first proposition.

If the inferred judgment already lies within the first one, so that it can be derived from it without needing a third, mediating representation, then this is called an “immediate inference.” I would rather call it an inference of the understanding. Examples of immediate inferences from “All humans are mortal”:

• “Some humans are mortal.”
• “Some mortal beings are human beings.”
• “Nothing immortal is a human being.” These propositions are thus immediate conclusions from the first one.

But if, in addition to the knowledge that serves as the ground, yet another judgment is necessary to produce the conclusion, then the inference is called a “syllogism” (a formal logical argument). On the other hand, the proposition “All scholars are mortal” does not lie directly within the underlying judgment “All humans are mortal” (because the concept “scholar” does not occur in it at all). It can be concluded from it only by means of an intermediate judgment (e.g., “All scholars are human”).

In every syllogism:

1. I first think a rule (the major premise) through the understanding.
2. Second, I subsume a piece of knowledge under the condition of the rule (the minor premise) by means of the power of judgment.
3. Finally, I determine my knowledge through the predicate of the rule (the conclusion), and this happens a priori through reason.

Thus, the relationship between a piece of knowledge and its condition, which the major premise represents as the rule, constitutes the different kinds of syllogisms. They are therefore threefold – just as are all judgments in general – distinguished by the way they express the relation of knowledge to the understanding: namely, categorical, hypothetical, or disjunctive syllogisms.

If, as usually happens, the conclusion is a judgment given as a problem (we want to see if it flows from already given judgments, through which a wholly different object is thought), then I look to see if the assertion of this conclusion can be found in the understanding under certain conditions, according to a universal rule. If I find such a condition, and if the object of the conclusion can be subsumed under the given condition, then this conclusion is derived from the rule that is also valid for other objects of knowledge. From this, we see that reason, in the process of inferring, seeks to bring the greatest variety of the understanding’s knowledge to the smallest number of principles (universal conditions). By doing so, it aims to create the highest possible unity within that variety of knowledge.

C. On the Pure Use of Reason

Can we isolate reason? And if so, is it then a genuine source of concepts and judgments that arise solely from it, and thereby refer to objects? Or is reason only a merely subordinate faculty that gives a certain form, called “logical” form, to already given knowledge? Through this logical form, different pieces of knowledge from the understanding are subordinated to one another, and lower rules are subordinated to higher ones (whose condition includes the condition of the lower rules in its scope), as far as this can be achieved through comparing them. This is the question with which we will now concern ourselves, though only provisionally for now.

Indeed, the variety of rules and the unity of principles is a demand of reason. Reason wants to bring the understanding into a complete and thorough connection with itself, just as the understanding brings the variety of intuition under concepts and connects them through concepts. Yet, such a principle of reason does not dictate any law to objects themselves. It does not contain the basis for the possibility of knowing and determining objects as such in general. Rather, it is merely a subjective law of efficiency for our understanding. Its purpose is to help our understanding, through the comparison of its concepts, reduce their universal use to the smallest possible number. This principle does not justify us in demanding that objects themselves possess such uniformity (which might make things easier for our understanding or help it extend itself). Nor does it give objective validity to our reason’s guiding maxims. In a word, the question is: Does reason in itself – that is, pure reason – contain a priori synthetic principles and rules (knowledge-expanding rules known before experience)? And what might such principles consist of?

The formal and logical procedure of reason in syllogisms (logical arguments) already gives us enough guidance about where the basis of its transcendental principle will be found when it comes to synthetic knowledge gained through pure reason.

First, regarding syllogisms: A syllogism does not deal directly with intuitions (direct sensory awareness) in order to bring them under rules, as the understanding does with its categories. Instead, a syllogism deals with concepts and judgments. Therefore, if pure reason also deals with objects, it does not have an immediate reference to them and their intuition. It deals only with the understanding and its judgments. These judgments, in turn, apply directly to the senses and their intuition in order to determine their object. The unity of reason is therefore not the unity of a possible experience. It is essentially different from that unity, which is the unity of understanding. The principle that “everything which happens must have a cause” is not a principle known or prescribed by reason at all. It makes the unity of experience possible and borrows nothing from reason. Reason, working with mere concepts, could not have imposed any such synthetic unity without this reference to possible experience.

Second, regarding reason’s logical use: In its logical use, reason seeks the universal condition of its judgment (its conclusion). The syllogism is nothing but a judgment made by bringing its condition under a universal rule (the major premise). Now, since this rule is, in turn, subjected to this same attempt by reason (to find the condition of its condition, by means of further syllogisms, as far as we can go), we see very well that the proper principle of reason in general (in its logical use) is to find the unconditioned for the conditioned knowledge of the understanding. With this unconditioned, the unity of reason will be completed.

But this logical maxim (to seek the unconditioned) cannot become a principle of pure reason unless we assume something further: that when the conditioned is given, then the entire series of conditions subordinated one to another – a series which is itself unconditioned – is also given (i.e., it is contained in the object and its connection to other things).

Such a principle of pure reason, however, is obviously synthetic. The conditioned is analytically (by definition) related to some condition, but it is not analytically related to the unconditioned. Different synthetic propositions must arise from this principle. The pure understanding knows nothing of these propositions, since it only deals with objects of a possible experience, whose knowledge and synthesis (combination) are always conditioned. But the unconditioned, if it actually occurs, needs to be considered particularly according to all the characteristics that distinguish it from everything conditioned. It must thereby give us material for many synthetic a priori propositions.

The principles arising from this supreme principle of pure reason (to seek the unconditioned) will, however, be transcendent with respect to all appearances. This means that no adequate empirical use can ever be made of that principle. It will therefore be entirely distinct from all principles of the understanding (whose use is completely immanent, meaning it stays within the bounds of experience, because it only has the possibility of experience as its subject matter).

But several critical questions arise:

• Does the principle – that the series of conditions (in the combining of appearances, or even in the thinking of things in general) reaches to the unconditioned – actually have objective correctness or not?
• What consequences follow from it for the empirical use of the understanding?
• Or, does it instead yield no such objectively valid propositions at all? Is it only a logical instruction that tells us, in our ascent to ever higher conditions, to approach completeness in them and thus to bring the highest possible unity of reason into our knowledge?
• Has this need of reason, I ask, been misunderstood as a transcendental principle of pure reason, which too hastily assumes such an unlimited completeness in the series of conditions within the objects themselves?
• And if so, what other kinds of misinterpretations and delusions may have crept into the inferences of reason? These are inferences whose major premise (which is perhaps more a wish than a proven starting point) is taken from pure reason and ascends from experience to its conditions.

All this will be our concern in the Transcendental Dialectic. We will now develop this Dialectic from its sources hidden deep in human reason. We will divide it into two main parts:

1. The first part will discuss the transcendent concepts of pure reason.
2. The second part will discuss reason’s transcendent and dialectical inferences of reason.

II. Transcendental Doctrine of Method

This is the second main part of our larger study. It is called the Transcendental Doctrine of Method.

Previously, in the “Transcendental Doctrine of Elements,” we looked at the basic building blocks of pure reason – things like the forms of our sensibility (space and time) and the pure concepts of our understanding.

Now, the Doctrine of Method will focus on something different. It will determine the formal conditions for creating a complete system of pure reason. Think of it as the “how-to” guide for using these elements. It will outline the plan and procedures for organizing our pure, a priori knowledge (knowledge independent of experience) into a structured and secure system. This part will explore how pure reason should proceed to build its own edifice correctly.