ABSTRACT
This chapter focuses on adult second language (L2) acquisition and addresses several learnability issues raised by this language learning process. It presents a discussion of several ways in which the adult L2 acquisition process can uniquely inform us concerning the representation of Universal Grammar and language-specific grammars. The chapter provides a demonstration of how the saidy of L2 acquisition can clarify the nature of several noncore processes involved in language learning. In support of the Separation Hypothesis, there is a conceptual argument from the case of the bilingual child learner. The chapter investigates the acquisition of the head-direction parameter by 21 adult Japanese speakers learning English as a second language. It describes several ways in which the study of adult L2 acquisition provides critical evidence concerning the leamability of both core and peripheral aspects of grammar construction.
