Language--the most awesome of universal human achievements--develops with extraordinary speed over the early childhood years. In mastering language, children acquire four components--phonology, semantics, grammar, and pragmatics--that they combine into a flexible communication system.

Three theories provide different accounts of how children develop language. According to Skinner and other behaviorists, language is learned through operant conditioning and imitation. In contrast, Chomsky's nativist view regards children as biologically equipped with a language acquisition device that supports rapid early mastery of the structure of language. Interactionist theories offer a compromise between these two views, stressing that innate abilities and social contexts combine to promote language development.

During infancy, biological predispositions, cognitive development, and a responsive social environment join together to prepare the child for language. Newborn babies have a built-in capacity to detect a wide variety of sound categories in human speech. By the second half of the first year, infants become increasingly sensitive to the phonemes, words, and phrase structure of their native tongue.

Semantic development takes place with extraordinary speed as preschoolers fast map thousands of words into their vocabularies. Children's language comprehension develops ahead of production. Lexical contrast theory is a recent controversial account of how semantic development takes place. Preschoolers draw on many sources to deduce word meanings.

Children are active, rule-oriented learners whose earliest word combinations begin to reflect the grammar of their native tongue. In first combining words, children are preoccupied with figuring out the meanings of words and in getting their thoughts across to others. By age 6, children have mastered most of the grammar of their native tongue. Certain complex forms, however, continue to be refined in middle childhood.

During early and middle childhood, children acquire a variety of pragmatic devices that permit them to engage in more sustained and effective conversation with others. Parents the world over realize the importance of socially appropriate communication and tutor children in social routines from an early age. Although preschoolers show the beginnings of metalinguistic awareness, major advances do not take place until middle childhood.

Historically, Americans have held negative attitudes toward childhood bilingualism. A large body of research shows that children who are fluent in two languages are advanced in a variety of cognitive and metalinguistic skills.