Full Idea
A problem for the Humean theory of motivation is that it is disputed that beliefs are only representational states, which cannot, unlike desires, move us to act.
Gist of Idea
The Humean theory of motivation is that beliefs may be motivators as well as desires
Source
Pascal Engel (Truth [2002], §4.2)
Book Reference
Engel,Pascal: 'Truth' [Acumen 2002], p.110
A Reaction
This is a crucial issue for Humeans and empiricists. Rationalists claim that people act for reasons, so that reasons are intrinsically motivational (like the Form of the Good), and reasons may even be considered direct causes of actions.