 Isolated putative exceptions are called idioms— and natural languages contain many of them. (Jackendoff (1997) estimates the number of English idioms to be around twenty-five thousand. Defenders of the compositionality of natural languages sometimes argue that the syntactic complexity of these expressions is only apparent, and hence, they can be viewed as lexical items. But unless we are given clear non-semantic grounds for singling out idioms, the move is question-begging. Such criteria have been proposed, but they tend to be rather controversial; cf. Nunberg, Sag, and Wasow (1994).)