The emergence of an abstract grammatical category 1 The emergence of an abstract grammatical category in children’s early speech

How do children begin to use language to say things they have never heard before? The origins of linguistic productivity have been a subject of heated debate: While generativist accounts posit that childrens early language reflects the presence of syntactic abstractions, constructivist approaches instead emphasize gradual generalization over frequently-heard forms. Here we develop a Bayesian statistical model that measures the degree of abstraction implicit in childrens early use of the determiners “a” and “the.” Our work reveals that many previously-used corpora are too small to adjudicate between these theoretical positions. Several datasets, including the Speechome Corpus—a new ultra-dense dataset for one child—show evidence of low initial levels of productivity and higher levels later in development, however. These findings are consistent with the hypothesis that children lack rich grammatical knowledge at the outset of language learning, but rapidly begin to generalize on the basis of structural regularities in their input.