Learnability of syntax 1 Running head : LEARNABILITY OF SYNTAX

The learnability of abstract syntactic principles Children acquiring language infer the correct form of syntactic constructions for which they appear to have little or no direct evidence, avoiding simple but incorrect generalizations that would be consistent with the data they receive. These generalizations must be guided by some inductive bias – some abstract knowledge – that leads them to prefer the correct hypotheses even in the absence of directly supporting evidence. What form do these inductive constraints take? It is often argued or assumed that they reflect innately specified knowledge of language. A classic example of such an argument moves from the phenomenon of auxiliary fronting in English interrogatives to the conclusion that children must innately know that syntactic rules are defined over hierarchical phrase structures rather than linear sequences of words (e. Nakayama, 1987). Here we use a Bayesian framework for grammar induction to argue for a different possibility. We show that, given typical child-directed speech and certain innate domain-general capacities, an unbiased ideal learner could recognize the hierarchical phrase structure of language without having this knowledge innately specified as part of the language faculty. We discuss the implications of this analysis for accounts of human language acquisition. Introduction Nature, or nurture? To what extent is human mental capacity a result of innate domain-specific predispositions, and to what extent does it result from domain-general learning based on data in the environment? One of the tasks of modern cognitive science is to move past this classic nature/nurture dichotomy and elucidate just how innate biases and domain-general learning might interact to guide development in different domains of knowledge. Scientific inquiry in one domain, language, was influenced by Chomsky's observation that language learners make grammatical generalizations that appear to go beyond what is immediately justified by the evidence in the input (Chomsky, 1965, 1980). One such class of generalizations concerns the hierarchical phrase structure of language: children appear to favor hierarchical rules that operate on grammatical constructs such as phrases and clauses over linear rules that operate only on the sequence of words, even in the apparent absence of direct evidence supporting this preference. Such a preference, in the absence of direct supporting evidence, is used to suggest that human learners innately know a deep organizing principle of natural language, that grammatical rules are defined on hierarchical phrase structures. In outline form, this is the " Poverty of the Stimulus " (or …