language acquisition, the process of learning a native or a second language. The acquisition of native languages is studied primarily by developmental psychologists and psycholinguists. Although how children learn to speak is not perfectly understood, most explanations involve both the observation that children copy what they hear and the inference that human beings have a natural aptitude for understanding grammar. While children usually learn the sounds and vocabulary of their native language through imitation, grammar is seldom taught to them explicitly; that they nonetheless rapidly acquire the ability to speak grammatically supports the theory advanced by Noam Chomsky and other proponents of transformational grammar. According to this view, children are able to learn the "superficial" grammar of a particular language because all intelligible languages are founded on a "deep structure" of grammatical rules that are universal and that correspond to an innate capacity of the human brain. Stages in the acquisition of a native language can be measured by the increasing complexity and originality of a child's utterances. Children at first may overgeneralize grammatical rules and say, for example, goed (meaning went ), a form they are unlikely to have heard, suggesting that they have intuited or deduced complex grammatical rules (here, how to conjugate regular verbs) and failed only to learn exceptions that cannot be predicted from a knowledge of the grammar alone. The acquisition of second or foreign languages is studied primarily by applied linguists. People learning a second language pass through some of the same stages, including overgeneralization, as do children learning their native language. However, people rarely become as fluent in a second language as in their native tongue. Some linguists see the earliest years of childhood as a critical period, after which the brain loses much of its facility for assimilating new languages. Most traditional methods for learning a second language involve some systematic approach to the analysis and comprehension of grammar as well as to the memorization of vocabulary. The cognitive approach, increasingly favored by experts in language acquisition, emphasizes extemporaneous conversation, immersion, and other techniques intended to simulate the environment in which most people acquire their native language as children.
See J. C. Richards, Error Analysis: Perspectives on Second Language Acquisition (1974); R. Andersen, ed., New Dimensions in Second Language Acquisition Research (1981); D. W. Carroll, Psychology of Language (1986); A. Radford, Syntactic Theory and the Acquisition of English Syntax (1990).