The relation between Hume’s constructive and skeptical aims has been a central concern for Hume interpreters. Hume’s two definitions of ‘cause’ in the Treatise and first Enquiry apparently represent an important constructive achievement, but this paper argues that the definitions must be understood in terms of Hume’s skepticism. The puzzle I address is simply that Hume gives two definitions rather than one. I use Don Garrett’s interpretation as a foil to develop my alternative skeptical interpretation. Garrett claims the definitions exhibit (...) a general susceptibility to two kinds of definition that all “sense-based concepts” share. Against Garrett, I argue that the definitions express an imperfection Hume finds only in our concept of causation. That imperfection is absent from other sense-based concepts, and prompts skeptical sentiments in Hume’s conclusion to the Treatise’s Book 1. I close by comparing my interpretation with those of Helen Beebee, Stephen Buckle, Galen Strawson and Paul Russell. (shrink)