On the Testability of Theories of Language Evolution

this requirement, and the constraints on this requirement have not really been explored in the literature. We know, for instance, that in American Sign Language (henceforth ASL) and SASL (at least) a sentence may not contain more than two topics (except in a listing construction)4. Many sentences containing classifier predicates have at least three lexical NPs thematically, e.g., in a signed language utterance with the English meaning, "The woman put the cup on the table", but only two of the NPs may occur as topics. We thus examine what may and may not appear in topic positions in these constructions (and whether or not these restrictions are detennined by thematic roles). Further, we examine the syntactic relationship between classifier predicates and the items occurring in topic positions.