The merchant's toil, the sage's indolence,
The monk's humility, the hero's pride,
All, all alike, find Reason on their side.
(Pope, An Essay on Man, Epistle II, 172-4)Hume's moral philosophy is often interpreted as an example of a naturalistic approach to ethics. J.L. Mackie, for instance, writes that in Hume the questions of moral philosophy are answered ‘in sociological and psychological terms, by constructing and defending a causal hypothesis.’ Similarly, Páll S. Árdal claims that Hume ‘is concerned with an attempt to discover those psychological laws that explain human emotions (including moral emotions) and the behaviour of people in society.’ I argue in this essay that if Hume is read in this way as developing a general explanatory theory of moral sentiments, he faces an inescapable dilemma. Section I presents the dilemma. In sections II and ill, I argue why for Hume — interpreted as a proponent of general psychological laws — there is no way out of this dilemma.