What makes the words we speak mean what they do? Possible-worlds semantics articulates the view that the meanings of words contribute to determining which possible worlds would make a sentence true, and which would make it false. In the first book-length examination from this viewpoint, M.J. Cresswell argues that the nonsemantic facts on which semantic facts supervene are facts about the causal interactions between the linguistic behavior of speakers and the facts in the world that they are speaking about.