A hypothetical mechanism, based on generative grammar, introduced in 1964 by the US linguist and philosopher (Avram) Noam Chomsky (born 1928) to explain how children acquire internalized knowledge of grammar with remarkable speed on the basis of fragmentary and degenerate input data. The language acquisition device is assumed to be a biologically based innate capacity for language, independent of any specific natural language, that enables a child exposed to adult speech to implement certain general principles for discovering the grammatical rules of the specific language in question. Also called a language acquisition system (LAS). See also innate idea. LAD abbrev.