In the Critique of Pure Reason, Kant argues that traditional metaphysics inevitably leads to contradictions that can be resolved only by accepting Kant’s critical philosophy. However, Kant does not limit his discussion of such contradictions (which he calls “antinomies”) to the 1st Critique; instead, Kant continues to present and resolve new antinomies throughout his mature writings. My dissertation analyzes Kant’s overall antinomy theory, emphasizing the overlooked philosophical and historical importance of antinomies presented in Kant’s writings after the 1st Critique. These later discussions develop a theory of teleological purposiveness that substantially refines and clarifies the relationship between morality and nature in Kant’s philosophy. My dissertation critically evaluates this mature antinomy theory and, then, examines its reinterpretation and adaptation in the writings of Schelling and Hegel.