Recent advances in linguistic theory offer new proposals about the factors that are crucial to understanding the design and acquisition of languagethe genetic endowment, experience, and principles not specific to the language faculty. Of particular interest is the third of these factors, whose importance is now widely recognized, raising questions about its character, its role in shaping the language faculty, and its impact on the future of linguistic research. Contemporary linguistics has two major objectives, one descriptive and the other explanatory. On the one hand, there is the challenge of documenting how individual languages employ form to express meaning-e.g., how they use case, agreement and word order to distinguish among the participants in an event, how they encode contrasts involving time and space, how they convey new and old information, and so forth. On the other hand, there is the challenge of explaining why language has the particular properties that it does (the problem of language design) and how those properties emerge so reliably in the course of early childhood (the problem of language acquisition). It is the search for answers to these two problems that makes work in linguistics central to the larger enterprise of cognitive science. A signature thesis of linguistic theory for the last half century is the 'innateness hypothesis.' First put forward in the 1960s by Noam Chomsky, it posits two separate inborn mechanisms: a sensory system for the preliminary analysis of input and a Universal Grammar (1975Grammar ( :12, 2011. The idea of an innate sensory system is widely accepted, but the UG thesis has always been deeply divisive. Indeed, several branches of linguistics (syntax, language acquisition, and typology, to name three) have parallel research programs, one committed to UG and the other opposed. This schism notwithstanding, the playing field for explanatory initiatives is well bounded. As Chomsky (2005) observes, recapitulating the long-standing consensus, there are really just three factors that might be responsible for the character of language and for the ease with which it is acquired
