In the introductions to his third Critique, the Critique of Judgment, Kant claims that this work completes his critical project, for here he articulates and defends the principle of purposiveness without a purpose as the a priori, transcendental principle of judgment, the third and last main cognitive faculty to be treated in the critical philosophy. This principle is a necessary, transcendental principle of judgment, Kant argues, because it governs, justifies, and makes possible our aspirations to empirical knowledge, from its most basic form – our ability to formulate any empirical concepts – to its most sophisticated form – a complete, systematic science of empirical laws. This principle is, Kant claims moreover, “exhibited” paradigmatically in two forms of judgment: teleological judgment concerning organic behavior, and aesthetic judgment of natural beauty. In teleological judgment, we judge organisms to be “natural purposes” we judge that they function purposively. In aesthetic judging, we find objects to be purposive “for cognition,” or to be characterized by “purposive form.” The main text of the CJ comprises, correspondingly, two subsidiary Critiques, the Critique of Teleological Judgment (CTJ) and the Critique of Aesthetic Judgment (CAJ), devoted to these two forms of judgment.

As in the other Critiques, then, the argument of the third Critique comprises a justification of an a priori principle, as one that does and must govern activity of one of our fundamental cognitive capacities.