The language acquisition device (LAD) is the name given to a theoretical section of the brain posited to house the innate ability to acquire and recognize a first language. Put forth as theory by the linguist Noam Chomsky, the language acquisition device was said to be the seat of universal syntax shared by all humans. This theory of a congenital basis for formulating language, regardless of the native language spoken around the infant, has been hotly criticized by behaviorists and others who favor the notion that environment and nurturing are responsible for language acquisition.
The LAD theory posits that a set list of acceptable sentence structures — that is, possible combinations of subjects, verbs, objects, and modifiers — are known to children at birth. Though children rarely perfect grammar spoken during their early years, the LAD theory argues that with the sentence fragments and run on sentences of ordinary human speech and the innate universal grammar rules, children are able to flesh out a full language in just a few short years. According to the LAD theory, a child does not pass its early years just meaninglessly repeating words and phrases, but in observing grammar variations and supplemental rules to construct new variations on sentence structure.
The language acquisition device theory was first introduced in the 1950s. Noam Chomsky tied it into the nativist theory of language, which proposed that humans have an inborn capacity or instinct to aid in acquiring their mother tongues. This went in opposition to the behaviorist theories of learning set forth by B.F. Skinner, which allowed for no such biological instincts in the human species. To build on nativist theories, Chomsky asserted all people must utilize the LAD to acquire language.
By the 1970s, further research at MIT, where Noam Chomsky taught linguistics, was starting to move away from the theory of a language acquisition device. As new languages were studied in depth, the universal characteristics Chomsky hypothesized did not emerge. In the 1990s, Chomsky moved to an innate principles-and-parameters-of-constraints framework to explain the language acquisition of infants. Most linguists found this theory plausible. Linguists have continued their research into the language habits of children, however, and the rapidity and ease with which children acquire language has not yet been fully explained.