An analysis of intrasentential codeswitching patterns that refutes a common explanation is presented. It is suggested that the Matrix Language-Frame model, which claims codeswitching to be entirely a matter of sentence production, is inadequate to account for a common but hitherto unexplained phenomenon, the occurrence of "dummy" verbs under certain conditions in codeswitch utterances. It is suggested further that this phenomenon has a natural explanation within minimalist linguistic theory of grammatical competence. It is concluded that intrasentential codeswitching is not purely a performance or production phenomenon, but also involves aspects of linguistic competence. Contains 22 references. (MSE)