1 Verb learning as a probe into children ’ s grammars

Let us begin this chapter by asking what constitutes an explanation in linguistics and in the field of language development. Since Chomsky’s seminal work in generative grammar (Chomsky 1957, 1965), the research program of lingusitic theory has been set towards circumscribing the set of possible human languages. In an idealization of this program, one must first construct a set of phenomenological descriptions of individual languages. This description leads to the construction of individual grammars, viewed as the relevant cognitive state achieved by the speakers of those languages. Next, the comparison of particular grammars leads to the formation of general principles that underlie all of these grammars. 1 That is, we aim to understand the cognitive code that is shared by all humans who have the ability to acquire a language. Thus, the goal of comparative linguistics is not merely to account for the properties of extant languages but to use the existing languages to develop hypotheses about what patterns of properties might occur in other yet to be encountered languages. More generally, the goal of modern linguistics is to identify the range and limits of cross-linguistic variation, so as to understand the cognitive principles that underlie the spectrum of human language. For the field of language acquisition, the ultimate goal is to explain how language acquisition is possible and how it unfolds over time under varying conditions of exposure. To be sure, given the complexity of the acquisition task, language learners will