Universal grammar is a theory in linguistics, usually credited to Noam Chomsky, proposing that the ability to learn grammar is hard-wired into the brain. The theory suggests that linguistic ability manifests itself without being taught, and that there are properties that all natural human languages share.
A grammar is "a system of rules that expresses the correspondence between sound and meaning" for the sentences of a language, as Chomsky himself has repeatedly said. Thus, grammars are by definition structure-bound, language-specific. To apply 'grammar' to sets including more than one language means stretching the term beyond any possible usefulness. Grammar is simply not the right linguistic level to look for language universals.
Changing perspectives on Universal Grammar and variation in linguistic theory are reflected in changing approaches to Universal Grammar and variation in second language acquisition research. Earlier questions such as 'Is there access to Universal Grammar?' has been replaced by questions about which linguistic properties are subject to transfer, why transfer is persistent in some cases but not others, why some properties are harder to acquire than others.
Philip Lieberman writes that he objects only to “biologically implausible formulations” of Universal Grammar “that do not take account of genetic variability.” In response, Lord Zuckerman observes correctly that it is a “truism” that a “genetically based ‘universal grammer’ ” will be subject to variability.
What's the relationship between heredity and environment for human language? The language organ interacts with early experience and matures into the grammar of the language that the child speaks. If a human being with this fixed endowment grows up in Philadelphia, as I did, his brain will encode knowledge of the Philadelphia dialect of English... The brain's different linguistic experience would modify the language organ's structure.
Chomskyan or ‘‘generative’’ linguistics is ﬁrst and foremost a theory about the acquisition of language, rather than about the language that is acquired; its accounts of the latter derive primarily from the requirements of the former, from what we know the language must be like in order for it to be acquired. Acquisition of the language, it claims, cannot be the product of general intelligence and must be done on the basis of a specialized and innate biological capacity.
English contains grammatical constructions that are called parasitic gaps... Constructions of this type -- where you can or cannot drop the pronoun -- are very rare. In fact, they are so rare that it is quite likely that during the period a child masters his native language (the first five or six years of life), he never hears any of these constructions, or he hears them very sporadically. Nonetheless, every native speaker of English knows flawlessly when you can and can't drop pronouns in these kinds of sentences.
So what Chomsky then said with respect to linguistic acquisition is that children could not guess the correct grammar if they had no pre-formed expectation and this innate expectation is Universal Grammar. In that context, grammar acquisition works in the following way: there’s an environmental input which consists of sample sentences for example, and then there’s a learning procedure, the child evaluates this environmental input. This learning procedure tells the child to choose one of the candidate grammars that are available to the child in the search space.
Darwin made a number of interesting comments about language evolution. For him, it was totally clear that human language emerged gradually from animal communication. He also compared languages to species in the sense that languages would compete with each other and some languages go extinct, and once languages were extinct, they never reappear, like species... Chomsky suggested that language might not have arisen by Darwinian evolution.
Until Chomsky propounded his theory of universal grammar in the 1960s, the empiricist school that had dominated thinking about language since the Enlightenment held that when children came into the world, their minds were like a blank slate... Subsequent research in the cognitive sciences, which combined the tools of psychology, linguistics, computer science, and philosophy, soon lent further support to the theory of universal grammar. For example, researchers found that babies only a few days old could distinguish the phonemes of any language and seemed to have an innate mechanism for processing the sounds of the human voice.
In Chomsky’s view, the reason that children so easily master the complex operations of language is that they have innate knowledge of certain principles that guide them in developing the grammar of their language. In other words, Chomsky’s theory is that language learning is facilitated by a predisposition that our brains have for certain structures of language.