Full Idea
The functionalist approach to the mind needs to invoke assumptions about what desires are for and beliefs are about, in order to infer what agents will do.
Gist of Idea
Functionalism needs causation and intentionality to explain actions
Source
David Papineau (Philosophical Naturalism [1993], 3.2)
Book Reference
Papineau,David: 'Philosophical Naturalism' [Blackwell 1993], p.57
A Reaction
Isn't the idea that you discover what desires are for and what beliefs are about by examining their function, and what the agent does? Which end should we start?