Language acquisition device or LAD is the innate human ability to learn a language.It is the key concept in Chomsky’s theory of UG. According to Chomsky we the humans have the innate capacity called DAD to learn a language. It is considered as a sort of mechanism or apparatus .The key features of the LAD are as follows.
The LAD is specis-specific. That means it distinguishes man from other primats.
The LAD is specific for language learning only and is opposed to the acquisition of other forms of behaviour or knowledge.
The LAD prestructures the properties of grammar to a large extent.
The LAD is like a biological organ. Like the physical organs of the body ,LAD also grows with the maturation of a child’s mind. That is, in its fundamental character it is innate and determined by the genetic structure of the organism. Of course, they grow under particular environmental conditions, assuming a specific form that admits of some variation.The comparatively crude structures of the child’s sentences may be that the language faculty in the mind has not yet fully come into being.LAD itself develops over the time rather than being constant from birth.
Thus, the LAD box is an inventory of principles and parameters. According to this framework, principles and parameters are part of a genetically innate universal grammar (UG) which all humans possess, barring any genetic disorders. As such, principles and parameters do not need to be learned by exposure to language. Rather, exposure to language merely triggers the parameters to adopt the correct setting.