For most philosophers, including Kantians of various stripes, the importance of the third Critique rests primarily in its containing a systematic account of Kant’s aesthetics, while others focus their attention on its presentation of his views on teleology and the philosophy of biology, and still others, including myself, pair its two introductions with the Appendix to the Dialectic in the first Critique in order to find therein Kant’s vindication of inductive reasoning against a Humean skepticism.1 But despite this variety of concerns, which speaks to the complexity of the work, it may seem strange to find a full chapter devoted to it in a book supposedly concerned with Kant’s account of free will. The explanation for this is that among the main concerns of the third Critique is the relation between nature and freedom, which we have already seen was a central concern of Kant throughout his philosophical career. The problem takes three forms. The first, which finds its definitive formulation in the first Critique, is to show that freedom, considered as a mode of causality involving absolute spontaneity or a capacity for first beginnings, is compatible with the causality of nature, conceived as mechanistic in a broad sense, wherein every “beginning,” conceived as a coming to be in time, preceded by an occurrence from which it follows necessarily in accordance with a rule. Since these modes of causality are deemed mutually exclusive, the task is to show that they could be predicated simultaneously, without contradiction, of the same action and agent, which Kant does by appealing to transcendental idealism. And we further saw that, while the first Critique is content to establish merely the logical possibility of such predication, since that is all that is thought necessary to resolve the Third Antinomy, the second Critique considers this as a starting point and by appealing to the fact of reason takes the further step of arguing for the reality of such freedom through the practical use of pure reason.