An important issue for the cognitive sciences is whether grammar is to any nontrivial extent an autonomous cognitive system. Current cognitive hypotheses of language acquisition would argue against an autonomous linguistic system and would support the notion that language emerges from more general cognitive knowledge and is throughout its development fundamentally tied to a nonlinguistic cognitive base. This paper explores this issue and presents data from case studies of children showing clear dissociations between language and nonlanguage cognitive abilities. The implications of such data are discussed. The major implications appear to be that lexical and relational semantic abilities are deeply linked to broader conceptual development but morphological and syntactic abilities are not. The development of a normal linguistic system, however, one in which grammar is systematically related to meaning, requires concurrent and concomitant linguistic and nonlingustic cognitive development.