Critique of Pure Reason

Lore & Background

In the preface to the first edition, Kant explains that by a "critique of pure reason" he means a critique "of the faculty of reason in general, in respect of all knowledge after which it may strive independently of all experience" and that he aims to decide on "the possibility or impossibility of metaphysics". Kant argues through transcendental idealism that objects are mere representations and not things in themselves, and that their form of appearance consists only of sensible forms of our intuition. This grants the possibility of a priori knowledge, since objects as appearance must conform to our cognition.

Kant distinguishes between analytic and synthetic judgments. A proposition is analytic if the predicate-concept is already contained within the subject-concept; for example, "All bodies are extended" is analytic. A proposition is synthetic if the predicate-concept is not contained within the subject-concept, as in "All bodies are heavy".

Before Kant, philosophers held that all a priori knowledge must be analytic. Kant, however, argues that knowledge of mathematics, first principles of natural science, and metaphysics is both a priori and synthetic. The central problem of the Critique is therefore to answer the question: "How are synthetic a priori judgments possible?"

Reader's Guide

The Critique of Pure Reason is considered a culmination of several centuries of early modern philosophy and an inauguration of late modern philosophy. Though it received little attention when first published, it later attracted attacks from both empiricist and rationalist critics and became a source of controversy. It has exerted an enduring influence on Western philosophy and helped bring about the development of German idealism.

Kant's work was stimulated by his decision to take seriously Hume's skeptical conclusions about basic principles such as cause and effect, which had implications for Kant's grounding in rationalism. Kant rejected analytical methods for deriving cause and effect, arguing that analytic reasoning cannot tell us anything not already self-evident, and sought to demonstrate how synthetic a priori knowledge is possible. This question is central because Kant contends that all important metaphysical knowledge is of synthetic a priori propositions; if it is impossible to determine which such propositions are true, then metaphysics as a discipline is impossible.

Did You Know?

• Kant uses the example '7 + 5 = 12' to argue that pure mathematics is synthetic though a priori, since no analysis of 7 or 5 will find 12.
• The work was set down in written form in just four to five months, while Kant was also lecturing and teaching, but is a summation of twelve years of philosophical development.
• Kant states that it was the remembrance of David Hume which first interrupted his 'dogmatic slumber' and gave his investigations a completely different direction.