In his early writings, Kant says that the solution to the puzzle of how morality can serve as a motivating force in human life is nothing less than the “philosophers’ stone.” In this dissertation I show that for years Kant searched for the philosophers’ stone in the concept of “respect” (Achtung), which he understood as the complex effect practical reason has on feeling. -/- I sketch the history of that search in Chapters 1-2. In Chapter 3 I show that Kant’s (...) analysis in Groundwork I is incomplete because it does not explain how respect functions as a feeling in motivating choice. In Chapter 4 I argue that Kant’s subsequent attempt to sidestep this explanation in Groundwork III is unsuccessful, and that his position remains open to a skeptical threat. The argument in the second Critique, which I reconstruct in Chapters 5-6, overcomes this threat, and in doing so explains how the feeling of respect is both painful and pleasurable. -/- In the course of defending these claims, I provide an alternative reading of the shift in Kant’s ethical project from the Groundwork of 1785 to the second Critique of 1788 Against a common view in the literature, I argue that the shift does not concern the direction of Kant’s deduction (from freedom to morality, or morality to freedom); rather, it concerns his view of human sensibility and the resources he thinks we have to make our practical self-understanding intelligible. In the second Critique, I argue, Kant develops a novel approach to moral feeling from the perspective of the human agent; and this in turn clears room in his ethics for a new kind of a priori knowledge—namely, knowledge of what the activity of practical reason must feel like. By way of conclusion, I offer a few reasons for why the form of Kant’s argument in the second Critique is still relevant today, as it shows why we can only address moral skepticism from a first-personal perspective. (shrink)