Hume begins the Treatise of Human Nature by announcing the goal of developing a science of man; by the end of Book 1 of the Treatise, the science of man seems to founder in doubt. Underlying the tension between Hume's constructive ambition – his ‘naturalism’– and his doubts about that ambition – his ‘skepticism’– is the question of whether Hume is justified in continuing his philosophical project. In this paper, I explain how this question emerges in the final section of Book 1 of the Treatise, the ‘Conclusion of this Book’, then examine Janet Broughton's and Don Garrett's answers to it, and conclude by sketching a different approach to this question.