8. Frequency effects in children's syntactic and morphological development

We have long loved Langendoen (1970) — a paper on the theoretical justification of “transformations, their effects on the structure of sentences, and the conditions under which they are optional or obligatory” (p. 102). In that paper, Langendoen argued that acceptability and grammaticality are “partially independent [and] partially dependent notions” (p. 103). We are struck by the implications of this contrast for language learning. If the learner’s grammar is a set of probabilistic patterns and not (also or instead) a set of grammatical rules, one might expect high frequency elements to be ‘grammatical’ and low frequency elements to be ‘ungrammatical.’ In other words, grammaticality and acceptability should be similar if frequency is the determining factor. But Langendoen (1970) hypothesized that grammatical competence contributes to grammaticality while processing factors contribute to acceptability. Our research shows clearer effects of frequency on the latter than the on former and thus relates to Langendoen’s observation.

This chapter explores the role of frequency in children’s syntactic and morphophonological development. One study compares relative clauses involving different extraction sites, which constructions vary considerably in their frequency of occurrence. Children’s production of these relatives suggests that frequency affects sentence planning, but their judgments of the same relatives are out of synchrony with the frequency rates. The other study presented here concerns the a and an forms of the indefinite article, which distinction is acquired relatively late even though the forms occur frequently. These studies show that frequency cannot be the whole story. We conclude that children’s mastery of a system of rules proceeds — at least to some extent — independently of frequency patterns in the input.