THE IMPORTANCE OF FIVE CONTEMPORARY THEORIES IN SECOND LANGUAGE ACQUISITION. COMPLEMENTARY LENSES ON SECOND LANGUAGE DEVELOPMENT

Second language acquisition (SLA) is a theoretically plural field in which no single account has achieved consensus; rather, a set of complementary theories each illuminates a different facet of how additional languages are learned. This article examines the importance of five contemporary theories that together define much of the current landscape: the Interaction Approach, Sociocultural Theory, Skill Acquisition Theory, Complex Dynamic Systems Theory, and usage-based (emergentist) approaches. For each, the article outlines the central constructs, summarises the empirical and conceptual contribution the theory makes, and considers its implications for language teaching. It argues that the significance of these frameworks lies less in their competition than in their complementarity: the Interaction Approach specifies the conditions under which input becomes usable; Sociocultural Theory locates development in mediated social activity; Skill Acquisition Theory explains the proceduralisation of knowledge through practice; Complex Dynamic Systems Theory reconceives development as nonlinear and emergent; and usage-based approaches ground acquisition in the statistical properties of input. Understanding these theories equips researchers and teachers with a repertoire of explanatory lenses, each answering questions the others leave open, and collectively advancing a fuller account of second language development.