Full Idea
Possible states of affairs have often been taken to be propositions, but this cannot be correct, since any possible state of affairs is possibly a state of affairs, but no proposition is possibly a state of affairs.
Gist of Idea
Possible states of affairs are not propositions; a proposition can't be a state of affairs!
Source
Kit Fine (The Problem of Possibilia [2003], 2)
Book Reference
'The Oxford Handbook of Metaphysics', ed/tr. Loux,M /Zimmerman,D [OUP 2005], p.163
A Reaction
The point is, presumably, that the state of affairs cannot be the proposition itself, but (at least) what the proposition refers to. I can't see any objection to that.