Hume’s Treatise of Human Nature pursues a naturalistic project of providing an “anatomy” of the human mind alongside the development of a series of skeptical arguments. Implicit in Hume's philosophy is a distinction between epistemological skepticism and conceptual skepticism.  The former aims to show that some class of beliefs lacks epistemic warrant. By contrast, the latter aims to show that a class of beliefs is unintelligible, incomprehensible, or contentless. My dissertation, Ideas and Intelligibility: Hume's Conceptual Skepticism, is a study of Hume's conceptual skepticism in the Treatise. It is orthodoxy among commentators that conceptual skepticism is of peripheral concern to Hume, its importance dwarfed by that of his naturalistic ambitions and epistemological skepticism. I show that this underestimates the scope, force, and sophistication of Hume's conceptual skepticism. Attention to conceptual skepticism allows us to resolve longstanding interpretive problems and sheds new light on the epistemology of the Treatise.