Full Idea
Anything that is a thinker at all has a thought with a certain content in virtue of being in a state which occupies a certain functional role.
Gist of Idea
A particular functional role is what gives content to a thought
Source
David Lewis (On the Plurality of Worlds [1986], 2.3)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.106
A Reaction
So often Lewis seems to get things the wrong way round. Maybe if you invert his entire (fabulously consistent) philosophy, you get the right answer? I take the content to be what makes the role possible.