Critique of Pure Reason: Encyclopedia - Critique of Pure Reason

Critique of Pure Reason

The Critique of Pure Reason (Kritik der reinen Vernunft), first published in 1781 with a second edition in 1787, is widely regarded as the most influential and widely read work of the German philosopher Immanuel Kant and one of the most influential and important in the entire history of Western philosophy. It is often referred to as Kant's "first critique", and was followed by the Critique of Practical Reason and the Critique of Judgment.

Regarded as a ground-breaking work in Western philosophy, Kant saw the first critique as an attempt to bridge the gap between rationalism and empiricism and, in particular, to counter the radical empiricism of David Hume.

Critique of Pure Reason - Kant's rejection of Hume's empiricism

Hume's conclusions, Kant realized, rested on the premise that knowledge is empirical at its root. The problem that Hume identified was that basic principles like cause and effect cannot be empirically derived. Kant's goal, then, was to find some way to derive cause and effect without relying on empirical knowledge. Kant rejects analytical methods for this, arguing that analytic reasoning can't tell you anything that isn't already self-evident. Instead, Kant argued that we would need to use synthetic reasoning. But this posed a new problem—how can one have synthetic knowledge that is not based on empirical observation—that is, how can we have synthetic a priori truths.

Kant concluded that there are synthetic a priori truths. He reasoned that geometry and Newtonian physics are synthetic a priori knowledges and are fundamentally true and wanted to establish how this could be possible. This also led him to inquire whether it could be possible to ground synthetic a priori knowledge for a study of metaphysics, because most of the principles of metaphysics from Plato through Kant's immediate predecessors made assertions about the world or about God or about the soul that were not self-evident but which could not be derived from empirical observation. This led to his most influential contribution to metaphysics: the abandonment of the quest to try to know the world as it is "in itself" independent of our sense experience. He demonstrated this with a thought experiment, showing that we cannot meaningfully conceive of an object that exists outside of time and has no spatial components and isn't structured in according with the categories of the understanding, such as substance and causality. Although we cannot conceive of such an object, Kant argues, there is no way of showing that such an object does not exist. Therefore, Kant says, metaphysics must not try to talk about what exists, but instead about what is experienced and how it is experienced.

This provided Kant with the basis to distinguish between phenomena -- things as they appear to our senses (including the inner sense of time) -- and noumena -- things that are purely objects of thought independently of sense perception, which, by definition, we can never experience -- in Kant's words, "thoughts without content [are] empty, and intuitions without concepts [are] blind". The phenomenon is only the representation of the noumenon that a person receives through their sensibilities and structures in accordance with the categories of the understanding. The noumenon exists as the horizon of our experience of a thing, a horizon that can only be circumscribed with philosophical concepts. Kant's whole metaphysical system, which is based on the operations of cognitive faculties, was meant to describe the world as we experience it—a much more modest task than describing the world as it is beyond our experience of it, which, according to Kant, is what all previous philosophy was mistakenly trying to do.

Kant termed his critical philosophy "transcendental idealism", which for him is intimately linked with empirical realism. That is, our empirical knowledge is real, but it cannot know what transcends the operations of our cognitive faculties. Transcendental idealism describes Kant's method of seeking the conditions of the possibility of our knowledge of the world and recognizes that there are things that transcend the limits of our cognitive faculties. It is because of taking into account the role of our cognitive faculties in structuring the known and knowable world that in the second preface to the "Critique of Pure Reason" Kant compares his critical philosophy to Copernicus' revolution in astronomy. Kant writes: "Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge" [Bxvi]. Just as Copernicus revolutionized astronomy by changing the point of view and taking the position of the observer into account, Kant's critical philosophy takes into account the position of the knower of the world in general and reveals its impact on the structure of his known world.

Kant's transcendental idealism should be distinguished from idealistic systems such as Berkeley's. While Kant claimed that phenomena depend upon the conditions of sensibility, space and time, and on the synthesizing activity of the mind manifested in the rule-based structuring of perceptions into a world of objects, this thesis is not equivalent to mind-dependence in the sense of Berkeley's idealism. For Berkeley, something is an object only if it can be perceived. For Kant, on the other hand, perception does not provide the criterion for the existence of objects. Rather, the conditions of sensibility (space and time) and the categories of the understanding provide the "epistemic conditions", to borrow a phrase from Henry Allison, required for us to know objects in the phenomenal world.

Critique of Pure Reason - Kant's approach

The Critique of Pure Reason is an attempt to answer two questions: "What do we know?" and "How do we know it?".

Kant approaches the questions by looking at the relationship between knowledge based on reason (what we know purely logically, prior to or independently of experience, or a priori) and knowledge based on experience (what we know based on the input of our senses or a posteriori).

In Kant's view, a priori intuitions and concepts provide us with some a priori knowledge, which also provides the framework for our a posteriori knowledge. For example, Kant argues that space and time are not part of what we might regard as objective reality, but are part of the apparatus of perception, and causality is a conceptual organizing principle that we impose upon nature.

In other words, space and time are a form of seeing and causality is a form of knowing. Both space and time and our conceptual principles and processes pre-structure our experience.

When we see a box as three-dimensional, the shape of the box may not be part of the box's nature. Kant argues that the spatio-temporal aspect of our perception of the shape of the box comes from us, in interaction with the box, not just from the box itself. When we experience events as causing other events, it is because we have a concept of causality in nature into which we fit our experience.

Things as they are "in themselves" are unknowable. For something to become an object of knowledge, it must be experienced, and experience is prestructured by the activity of our own minds -- both space and time as the forms of our intuition or perception, and the unifying, structuring activity of our concepts. These two aspects of our minds turn things-in-themselves into the world of our experience. We are never passive observers or knowers.

Kant's I—the Transcendental Unity of Apperception—is similarly unknowable. I am aware that there is an "I", subject, or self that accompanies all of my experience and consciousness. But since I only experience it in time, which is a "subjective" form of perception, I can never know directly that "I" that is appearing in time as it might be "in itself", outside of time. Thus we can never truly know ourselves as we might be outside of or prior to the forms through which we perceive and conceive ourselves.

Critique of Pure Reason - Transcendental Aesthetic

Kant separates the mind into two faculties, intuition and understanding. The Transcendental Aesthetic is that part of the CPR that considers the contribution of intuition to our knowledge or cognition. In discussing intuition Kant says: "In whatever manner and by whatever means a mode of knowledge may relate to objects, intution is that through which it is in immediate relation to them" (A19/B33). Intuition is responsible for providing the mind with objects, or what Kant calls "appearances". Kant then goes on to distinguish between the matter and the form of appearances. The matter is "that in the appearance which corresponds to sensation" (A20/B34). The form is "that which so determines the manifold of appearance that it allows of being ordered in certain relations" (A20/B34). Kant's revolutionary claim is that the form of appearances — which he later identifies as space and time — is a contribution made by the faculty of intuition to cognition, rather than something that exists independently of the mind. This is Kant's doctrine that space and time are transcendentally ideal.

Kant's arguments for this conclusion are widely debated amongst Kant scholars. Some see the argument as based on Kant's conclusions that our representation of space and time is an a priori intuition. From here Kant is thought to argue that our representation of space and time as a priori intuitions entails that space and time are transcendentally ideal (see Henry Allison, "Kant's Transcendental Idealism"). Others see the argument as based upon the question of whether synthetic a priori judgments are possible. Kant is taken to argue that the only way synthetic a priori judgments, such as those made in geometry, are possible is if space is transcendentally ideal.

Critique of Pure Reason - Transcendental Logic

The Transcendental Logic is that part of the CPR where Kant investigates the understanding and its role in constituting our knowledge. The understanding is defined as the faculty of the mind which deals with concepts (A51-52/B75-76). The Logic is divided into two parts: the Analytic and the Dialectic. In the Analytic Kant investigates the contributions of the understanding to knowledge. In the Dialectic Kant investigates the limits of the understanding.

The idea of a transcendental logic is that of a logic which gives an account of the origins of our knowledge as well as its relationship to objects. This is contrasted by Kant with the idea of a general logic, which abstracts from the conditions under which our knowledge is acquired, and from any relation that knowledge has to objects.

Critique of Pure Reason - Transcendental Analytic

The Transcendental Analytic is divided into an Analytic of Concepts and an Analytic of Principles, as well as a third section concerned with the distinction between phenomena and noumena. The main sections of the Analytic of Concepts are The Metaphysical Deduction and the Transcendental Deduction of the Categories. The main sections of the Analytic of Principles are the Schematism, Axioms of Intuition, Anticipations of Perception, Analogies of Experience, Postulates and The Refutation of Idealism.

In the Metaphysical Deduction Kant aims to derive the pure concepts of the understanding (what he also calls "categories") from the logical forms of judgment. In the Metaphysical Deduction Kant introduces his table of judgments which he uses to guide the derivation of the table of categories.

In the Transcendental Deduction Kant aims to show that the categories are applicable to the objects of experience which are given to us through intuition. Kant rewrote the entire Transcendental Deduction for the second edition of the Critique, published 6 years after the first edition.

In order to answer criticisms of the Critique of Pure Reason that Transcendental Idealism denied the reality of external objects, Kant added a section to the second edition (1787) entitled "The Refutation of Idealism" that turns the "game" of idealism against itself by arguing that self-consciousness presupposes external objects in space. Defining self-consciousness as a determination of the self in time, Kant argues that all determinations of time presuppose something permanent in perception and that this permanent cannot be in the self, since it is only through the permanent that one's existence in time can itself be determined. This argument inverted the supposed priority of inner over outer experience that had dominated philosophies of mind and knowledge since Descartes.

Critique of Pure Reason - Transcendental Dialectic

Critique of Pure Reason - Terms

Critique of Pure Reason - Intuition

"Intuition" is "the faculty or power of receiving representations"(see Second Part, Transcendental Logic, Of Logic in General). Objects are given to use through intuition. Intuition can be pure or empirical.

Pure intuition contains the a priori forms under which objects of senses can be intuited—such as the space and time. Without these a priori forms, objects of senses cannot be perceived or thought of. Pure intuition is only possible a priori.

Empirical intuition includes sensation—which presupposes the actual presence of an object. It is only possible a posteriori.

See also

• Norman Kemp Smith, author of the most commonly-used English translation of the Critique.
• Arthur Schopenhauer, The World as Will and Representation, Volume I, Appendix "Criticism of the Kantian Philosophy", Dover, ISBN 486-21761-2

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