We thank Vivian Cook, Sue Foster, Kevin Gregg, Eric Kellerman, Bill Rutherford, and two anonymous reviewers for their comments and suggestions, and acknowledge our debt to the important review articles by Bloom (1975) and Rutherford (1984).
There have been many changes in the way in which twentieth‐century researchers have perceived the relationship between theories of language and theories of language acquisition. In this review, we examine some of these changes in light of differences in expectations for the role of linguistic theories in describing what language learners acquire and explaining how they acquire it. We conclude that a theory of grammar will be a necessary component in our explanation of the L1 acquisition of formal properties of grammar, such as syntax, morphology and phonology, and may also be required to explain these aspects of L2 acquisition. Linguistic theories will play no role in other aspects of acquisition, equally important to our understanding of the overall acquisition process, and these must be accounted for in other ways.