The language first learned is called one's native language or mother tongue; both of these terms are figurative in that the knowledge of particular languages is not inherited but learned behavior. Nonetheless, since the mid-20th cent. linguists have shown increasing interest in the theory that, while no one is born with a predisposition toward any particular language, all human beings are genetically endowed with the ability to learn and use language in general.
According to transformational (or generative) grammar, introduced by Noam Chomsky in the 1950s, the idiosyncratic vocabulary and grammatical conventions of any natural language rest on a foundation of "deep structures," a universal grammar underlying all languages and corresponding to an innate capacity of the human brain. This theory implies not only that there are constraints on what may constitute an intelligible human language, but also that, however numerous or striking, the differences between any two languages are less fundamental than their similarities.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.