Full Idea
Linguistic representations of possible worlds have three problems: some descriptions are inconsistent (which worlds cannot be); we cannot have indiscernible descriptions (though some worlds might be so); and descriptions are limited by vocabulary.
Gist of Idea
Linguistic possible worlds have problems of inconsistencies, no indiscernibles, and vocabulary
Source
David Lewis (On the Plurality of Worlds [1986], 3.2)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.165
A Reaction
Lewis is wonderful at getting problems clearly on the table. I take the idea of possible worlds as linguistic entities to be a non-starter, because (as usual) animals do it too, when they think of possibilities, which even the dimmest ones must do.