One hotly debated issue is whether the biological contribution includes capacities specific to language acquisition, often referred to as universal grammar. For fifty years, linguists Noam Chomsky and the late Eric Lenneberg have argued for the hypothesis that children have innate, language-specific abilities that facilitate and constrain language learning.

Other researchers, including Elizabeth Bates, Catherine Snow, Brian MacWhinney, and Michael Tomasello, have hypothesized that language learning results from general cognitive abilities and the interaction between learners and their surrounding communities. Recent work by William O'Grady proposes that complex syntactic phenomena result from an efficiency-driven, linear computational system. O'Grady describes his work as "nativism without Universal Grammar."

One of the most important advances in the study of language acquisition was the creation of the CHILDES database by Brian MacWhinney and Catherine Snow.


Nativist theories hold that children are born with an innate propensity for language acquisition, and that this ability makes the task of learning a first language easier than it would otherwise be. These "hidden assumptions" allow children to quickly figure out what is and isn't possible in the grammar of their native language, and allow them to master that grammar by the age of three. Nativists view language as a fundamental part of the human genome, as the trait that makes humans human, and its acquisition as a natural part of maturation. They believe that children learning language are as natural and normal as dolphins learning to swim or songbirds learning to sing.

The possible existence of a critical period for language acquisition is another nativist argument. Critical periods are time frames during which environmental exposure is needed to stimulate an innate trait. Young chaffinches, for example, must hear the song of an adult chaffinch before reaching maturity, or else would never be able to sing. Nativists argue that if a critical period for language acquisition exists , then language acquisition must be spurred on by the unfolding of the genome during maturation. Much research on the critical age period or window of opportunity Linguist Eric Lenneberg stated, in a 1964 paper, that a critical period of language acquisition ends around the age of 12 years. He claimed that if no language is learned before then (see Feral children), it could never be learned in a normal and fully functional sense. This was called the "Critical period hypothesis." However, the opponents of the critical period hypothesis say that in this example the child is hardly growing up in a nurturing environment, and that the lack of language acquisition in later life may be due to the results of a generally abusive environment rather than being specifically due to a lack of exposure to language.

The critical period hypothesis of brain plasticity and learning capacity has been called into question. Other factors may account for differences in adult and child language learning. Children’s apparently effortless and rapid language acquisition may be explained by the fact that the environment is set up to engage them in frequent and optimal learning opportunities. By contrast, adults seem to have an initial advantage in their learning of vocabulary and syntax, but may never achieve native-like pronunciation.[4] A more up-to-date view of the Critical Period Hypothesis is represented by the University of Maryland, College Park instructor Robert DeKeyser. DeKeyser argues that although it is true that there is a critical period, this does not mean that adults cannot learn a second language perfectly, at least on the syntactic level. DeKeyser talks about the role of language aptitude as opposed to the critical period.