A revised version of this paper will appear in the proceedings of CLS 39. Using phonotactics to learn phonological alternations

1 Introduction Linguistic theory presents a search space of possible grammars. Under that theory, learning a language requires navigating that search space in order to find the correct grammar (the most restrictive grammar consistent with the overt data provided to the learner). The computational difficulty of that task depends almost entirely on the formal structure of the search space. Any plausible linguistic theory includes a very large number of possible grammars, too large to be exhaustively searched by a learner. An adequate account of language learning must explain how the learner relates to the formal structure of the grammar space so that it can find the correct grammar much more efficiently than by exhaustive search.