In this paper I argue that Kant's claims about conscience in his moral writings of the 1790s reveal a fundamental instability in his moral philosophy. The central issue is the relationship between the moral law as the form of universality and the judgment of individuals about specific cases. Against Thomas Hill's claim that Kant has only a limited role for conscience, I argue that conscience has a comprehensive role in Kantian deliberation. I unpack the claims about conscience in the Metaphysics of Morals to show that they describe conscience as both a basic act of self-consciousness and as an all-things-considered judgment. I outline the role of conscience in moral motivation, and argue that taken together Kant's writings about conscience reveal a way to rethink Kant's conception of the Fact of Reason.