This book integrates psycho-, socio- and applied linguistics to form a coherent approach to second language acquisition. The first section focuses on the use of variation theory as a means of examining language learners' speech. The second section deals with the place of Chomskyan linguistics in the field of cognitive science and the psychological reality of variable rules. Section three compares Krashen's (1981) theory of monitoring with Labov's (1972), proposing an alternative featuring the best aspects of both approaches.