The Transcendental Deduction of the categories is the heart of the Critique of Pure Reason. Here Kant argues that we are justified in applying pure concepts of the understanding to objects of experience. His strategy is to show that the categories are necessary conditions for experiencing objects given in intuition. Kant completely revised this section in the B edition; here we shall examine both the A and B edition versions, to understand what was lacking in the 1781 version. As many readers are disappointed to discover, both deductions treat the categories as a group. Not until the Principles of Pure Understanding does Kant defend individual categories.

In the A edition Preface to the Critique, Kant says the deduction of the categories “has two sides,” one objective, the other subjective. The objective side must “demonstrate and make comprehensible the objective validity of its concepts a priori” and thus is essential to his project. The subjective side is less essential and concerns “the powers of cognition on which [the understanding] rests” (Axvi–xvii). Many commentators have assumed that Kant is referring to two distinct proofs, one concerning conditions for experiencing objects, the other the subjective sources of experience. As we shall see, there is reason to reject this reading.

This chapter proceeds as follows. Section 1 treats the introduction, common to both editions, and then considers the question of the objective and subjective deductions.