Children acquiring a language will observe people around them using the language, and the set of expressions in the language which the child hears (and the contexts in which they are used) in the course of acquiring the language constitute the child’s linguistic experience of the language. This experience serves as input to the child’s language faculty, which provides the child with a set of procedures for analysing the experience in such a way as to devise a grammar of the language being acquired. Chomsky’s hypothesis that the course of language
acquisition is determined by an innate language faculty is known popularly as the innateness hypothesis.
Obviously, when people speak, they do make mistakes (although research has
shown that language addressed to children is almost completely free of such
mistakes). However, when this happens, there is no clear signal to the child
indicating that an adult utterance contains a mistake, that is, as far as the child is