Introduction

The argument of the poverty of the stimulus has maintained a central place in the development of Generative Grammar at least since Chomsky (1965). The argument runs like this: there is a piece of grammatical knowledge G that can be attributed to adult speakers of a language. Examination of the input shows that the ambient language (i.e. the language of the community that the first language learner is exposed to) does not uniquely determine G. That is, the primary linguistic data that the child is exposed to is compatible with a range of hypotheses that includes (but does not require) G. Given that adults know G and that G represents only one point in a range of hypotheses compatible with experience, it follows that G must be determined innately. In other words, all of the other hypotheses compatible with the primary linguistic data are excluded a priori. Learners acquire G because it is the unique point of intersection between the primary linguistic data and the innate hypothesis space.

In this paper, we present a novel consequence of the poverty of the stimulus. We will consider a case in which the learner's innate hypothesis space arguably provides at least two hypotheses that are compatible with the primary linguistic data. In this case, experience does not determine which of these is the correct grammar. Consequently, some learners acquire one grammar and others acquire the other.