Full Idea
No one has ever described a way of explaining what beliefs, desires, and other mental states are except in terms of actual or possible relations to things in the external world.
Gist of Idea
We can only describe mental attitudes in relation to the external world
Source
Gilbert Harman ((Nonsolipsistic) Conceptual Role Semantics [1987], 12.3.4)
Book Reference
Harman,Gilbert: 'Reasoning Meaning and Mind' [OUP 1999], p.226
A Reaction
If I pursue my current favourite idea, that how we explain things is the driving force in what ontology we adopt, then this way of seeing the mind, and taking an externalist anti-individualist view of it seems quite attractive.