It is argued that taken together, two widely held claims ((i) sentences express structured propositions whose structures are functions of the structures of sentences expressing them; and (ii) senteces have underlying structures that are the input to semantic interpretation) suggest a simple, plausible theory of propositional structure. According to this theory, the structures of propositions are the same as the structures of the syntactic inputs to semantics they are expressed by. The theory is defended against a variety of objections.