Full Idea
Functionalists take a "realist" approach to dispositions whereas the behaviourist embraces an "instrumentalist" line.
Clarification
'Instrumentalism' is the view that they are useful fictions, not real things
Gist of Idea
Are dispositions real, or just a type of explanation?
Source
Jaegwon Kim (Philosophy of Mind [1996], p. 78)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.78
A Reaction
A helpful distinction, which immediately shows why functionalism is superior to behaviourism. There must be some explanation of mental dispositions, and the instrumental view is essentially a refusal to think about the real problem.