Hume’s account of contrariety in Book I of the Treatise poses several interpretive puzzles. I consider each in turn and offer a novel interpretation of contrariety based on Hume’s discussion of the passions. That Book II and Book I form a complete chain of reasoning suggests that the way in which passions are related is analogous to the way in which ideas are related in the understanding. I argue that Hume identifies three species of empirical contrariety in Book II: contraries, (...) oppositions, and contradictions. All three species help clarify Hume’s remarks concerning contrariety in Book I. I further identify a second genus I call logical contrariety by drawing on Hume’s discussion of fictitious duration and distance. (shrink)