It is a claim made by [[Noam Chomsky]] positing that humans are born with some innate mental structure that aids in the acquisition of language. That is, there exists some universal grammar which represents what the rules of a human language could be. Then in the process of learning a language, the child learns structures that already conform to their innate language acquisition device. It is based on the poverty of stimulus argument that posits that children are not exposed to enough rich and complete data to account for the detailed grammatical knowledge that they do acquire.