The notion that language acquisition is a gradual process is not universally accepted. Indeed, many authors are much more impressed by the speed with which a child acquires a language. This was one of Chomsky's ( 1959) main arguments against the behaviorist position: the child simply acquires a language too quickly for this to be explained in terms of reinforcement and successive approximation. He cited the example of the immigrant child who has no difficulty acquiring the language of the new country, whereas the child's parents--in spite of their strong desire and motivation to learn the language--struggle ineffectively with it and impose the phonology and syntax of their first language on the new one.
The child's language acquisition feats so impressed Chomsky and the transformational grammar school that they maintained that the only explanation possible was that children are preprogrammed to acquire language at a definite point in their development. The view that the child possesses a capacity for language that the adult has lost is widely shared (e.g., Andersson, 1969; Jakobovits, 1972; Wilkins, 1972) and has been formalized in what is known as the "critical period" hypothesis.
In this chapter I examine the evidence for and against this hypothesis. Then language learning in childhood and adulthood is discussed, first by comparing adult second-language learning to the learning of a first language in childhood, and then by comparing adult second-language learning to second-language learning in childhood. We shall see that there are differences of opinion as to how similar these processes are.