Among Immanuel Kant’s (1724–1804) most influential contributions to philosophy is his development of the transcendental argument. In Kant’s conception, an argument of this kind begins with a compelling premise about our thought, experience, or knowledge, and then reasons to a conclusion that is a substantive and unobvious presupposition and necessary condition of this premise. The crucial steps in this reasoning are claims to the effect that a subconclusion or conclusion is a presupposition and