Answer: Language acquisition is one of the central topics in cognitive science. Every theory of cognition has tried to explain it. Probably no other topic has aroused such controversy. Possessing a language is the quintessentially human trait: all normal humans speak, no nonhuman animal does.
Noam Chomsky argues that children are born with a unique kind of knowledge which fits them for learning. This knowledge is embodied in a mechanism called the Language Acquisition Device or LAD. Chomsky believes that without postulating such a device it is impossible to understand how children master their native language in such a short time in spite of the highly abstract nature of the rules. This achievement would be particularly difficult without LAD in view of the fact that the everyday speech to which children are exposed is full of irregularities and deficiencies. According to Chomsky, it would be impossible for a child to learn the abstract system of a language from such degenerate data unless he had some prior knowledge about the general character of natural languages. He argues that since children must be equipped to learn any languages as a native language, the prior knowledge embodied in LAD must constitute that which is common to all languages, in other words, LAD must contain language universals. Universal Grammar specifies the allowable mental representations and operations that all languages are confined to use. The theory of universal grammar is closely tied to the theory of the mental mechanisms children use in acquiring language; their hypotheses about language must be couched in structures sanctioned by UG.
Chomsky argues his innateness hypothesis on basically three counts. Firstly, the existence of language universals. It is argued that the similarity in languages cannot possibly be due to anything other than a specific cognitive capacity in man. Everybody learns a language, not because they are subjected to a similar conditioning process, but because they possess an inborn capacity which permits them to acquire a language as a normal maturational process. This capacity is by definition universal.
The second count on which Chomsky argues his innateness hypothesis is the fact of language learning itself. He argues that the adult speech which a child hears around him is so poorly structured and impaired in performance (by hesitations, repetitions, false starts and so on) that he could not possibly learn language unless he brought to the task a very specific capacity. The ultimate product of LAD is an internalized system of rules which characterize the structure of a language, and which underlie both comprehension and production.
The third and the last count on which the innateness hypothesis is argued concerns the speed of acquisition of language. Language could not be learnt with the speed at which it is done unless the child was preprogrammed to do so.
According to behaviorists, the mind consisted of sensorimotor abilities plus a few simple laws of learning, governing gradual changes in an organism’s behavioral repertoire. Therefore, language must be learned, it cannot be a module. And thinking must be a form of verbal behavior, since verbal behavior is the prime manifestation of “thought” that can be observed externally. Chomsky argued that language acquisition falsified these beliefs in a single stroke: children learn languages that are governed by highly subtle and abstract principles, and they do so without explicit instruction or any other environmental clues to the nature of such principles. Hence language acquisition depends on an innate, species-specific module that is distinct from general intelligence. Much of the debate in language acquisition has attempted to test this once-revolutionary, and still controversial, collection of ideas.