 Prichard is mainly known for his work in moral philosophy, but the first of his very few publications were in epistemology. His main intellectual debt was to his teacher John Cook Wilson, whose thinking centered on topics in epistemology and what would now be called philosophical logic, rather than in ethics. In 1909 Prichard published his only book, Kant’s Theory of Knowledge, which was an account of Kant’s Transcendental Idealism. This book criticized Kant severely, and Prichard acknowledges that his main arguments against Kant originated from Cook Wilson. The book’s main conclusion is that ‘Knowledge is sui generis and therefore a ‘theory’ of knowledge is impossible. Knowledge is knowledge, and any attempt to state it in terms of something else must end in describing something which is not knowledge’ (p. 245). This view that a ‘theory’ of knowledge is impossible has its analogue in Prichard’s later argument that there can be no philosophical account of moral obligation of the sort that moral philosophers have traditionally tried to provide.