The “Striking Similarity” Between Kant’s Prolegomena and the Groundwork

When working on the Prolegomena , Kant remarked that there was a “striking similarity” between the central problem of his transcendental philosophy and that of moral philosophy, adding that he would present the solution to the latter shortly. Given that the Prolegomena deals with transcendental philosophy and his next book, the Groundwork , deals with moral philosophy, one might reasonably expect striking parallels between the two. At first glance, however, they appear quite dissimilar, and in the literature, they are not treated as closely related. In this essay, I argue that there are, in fact, remarkable similarities between the two works. They concern not only their central problems but also the method Kant uses to solve them, the types of arguments he develops in doing so, and even the terminology he uses to mark his steps. These similarities highlight both that Kant’s transcendental philosophy in the Prolegomena lays the groundwork for a metaphysics of nature and that his Groundwork for the metaphysics of morals is the moral counterpart to his transcendental philosophy. Moreover, they shed new light on crucial arguments of the Groundwork , especially on the beginning of the second section and the aim and argument of the third, thereby illuminating the structure of the argument of the book as a whole.