 The focus on truth conditions is not because Lewis thinks truth conditions are all that there are to languages. He acknowledges that languages also have ‘grammars’. A grammar, in Lewis’s sense, is a lexicon (i.e. a set of elementary constituents, along with their interpretation), a generative component (i.e. rules for combining constituents into larger constituents), and a representing component (i.e. rules for verbally expressing constituents). Lewis’s preferred interpretations are functions from possible worlds to extensions. So we can sensibly talk about the meaning of a non-sentential constituent of the language, but these meanings are derived from the truth conditions of sentences, rather than determining the meanings of sentences. That’s because, as we’ll see, what the conventions of language establish in the first instance are truth conditions for entire messages, i.e., sentences.