Full Idea
Everybody is a functionalist, in that we all hold that mental states are individuated, at least in part, by reference to their causal powers.
Clarification
'Individuated' means 'assigned identifying features'
Gist of Idea
Causal powers must be a crucial feature of mental states
Source
Jerry A. Fodor (Psychosemantics [1987], p.138)
Book Reference
Fodor,Jerry A.: 'Psychosemantics' [MIT 1993], p.138
A Reaction
I might individuate the Prime Minister by the carnation in his buttonhole. However, even a dualist must concede that we individuate mental faculties by their role within the mind.