Full Idea
Humeans claim that agents who believe they should act may nevertheless lack the desire to do so, where anti-Humeans must say the two go together, and someone with the belief thereby has the desire.
Gist of Idea
Humeans (unlike their opponents) say that desires and judgements can separate
Source
Michael Smith (The Moral Problem [1994], 4.7)
Book Reference
Smith,Michael: 'The Moral Problem' [Blackwell 1994], p.119
A Reaction
[very compressed] A very helpful distinction about the classic debates over the motivations of action. Smith defends the Humean view, and makes it very plausible. No mere sense of rightness or duty can compel us to act.