Language Replacement and the Spread of Tibeto-Burman

There has been a long-standing tradition in historical linguistics to seek internal explanations for linguistic change whenever possible, and to acknowledge contact as a cause of language change only when there is overt evidence in the form of evidently borrowed forms or constructions. In recent years we have begun to pay more attention to the ways in which contact and "interrupted transmission" (in the sense of McWhorter 2007) can radically affect the structure of a language, involving creolization processes as well as more familiar substratum and borrowing effects. It has long been clear that this is a central part of the history of Sinitic; in this paper I will argue that is more widely applicable to the expansion of Tibeto-Burman, and is an essential concept for explaining the striking variation in morphological complexity which we find across the family.