Theories

Theories about how language works in the human mind attempt to account for, among other things, how we associate meaning with the sounds (or signs) of language and how we use syntax—that is, how we manage to put words in the proper order to produce and understand the strings of words we call "sentences." The first of
these items—associating sound with meaning—is the least controversial and is generally held to be an area in which animal and human communication have at least some things in common (See animal communication). Syntax, on the other hand, is controversial, and is the focus of the discussion that follows.

There are essentially two schools of thought as to how we manage to create syntactic sentences: (1) syntax is an evolutionary product of increased human intelligence over time and social factors that encouraged the development of spoken language; (2) language exists because humans possess an innate ability, an access to what has been called a "universal grammar." This view holds that the human ability for syntax is "hard-wired" in the brain. This view claims, for example, that complex syntactic features such as recursion are beyond even the potential abilities of the most intelligent and social non-humans. (Recursion, for example, includes the use of relative pronouns to refer back to earlier parts of a sentence—"The girl whose car is blocking my view of the tree that I planted last year is my friend.") The innate view claims that the ability to use syntax like that would not exist without an innate concept that contains the underpinnings for the grammatical rules that produce recursion. Children acquiring a language, thus, have a vast search space to explore among possible human grammars, settling, logically, on the language(s) spoken or signed in their own community of speakers. Such syntax is, according to the second point of view, what defines human language and makes it different from even the most sophisticated forms of animal communication.

The first view was prevalent until about 1960 and is well represented by the mentalistic theories of Jean Piaget and the empiricist Rudolf Carnap. As well, the school of psychology known as behaviorism (see Verbal Behavior (1957) by B.F. Skinner) puts forth the point of view that language is behavior shaped by conditioned response. The second point of view (the "innate" one) can fairly be said to have begun with Noam Chomsky's highly critical review of Skinner's book in 1959 in the pages of the journal Language.[1] That review started what has been termed "the cognitive revolution" in psychology.

The field of psycholinguistics since then has been defined by reactions to Chomsky, pro and con. The pro view still holds that the human ability to use syntax is qualitatively different from any sort of animal communication. That ability might have resulted from a favorable mutation (extremely unlikely) or (more likely) from an adaptation of skills evolved for other purposes. That is, precise syntax might, indeed, serve group needs; better linguistic expression might produce more cohesion, cooperation, and potential for survival, BUT precise syntax can only have developed from rudimentary—or no—syntax, which would have had no survival value and, thus, would not have evolved at all. Thus, one looks for other skills, the characteristics of which might have later been useful for syntax. In the terminology of modern evolutionary biology, these skills would be said to be "pre-adapted" for syntax (see also exaptation). Just what those skills might have been is the focus of recent research—or, at least, speculation.

The conview still holds that language—including syntax—is an outgrowth of hundreds of thousands of years of increasing intelligence and tens of thousands of years of human interaction. From that view, syntax in language gradually increased group cohesion and potential for survival. Language—syntax and all—is a cultural artifact. This view challenges the "innate" view as scientifically unfalsifiable; that is to say, it can't be tested; the fact that a particular, conceivable syntactic structure does not exist in any of the world's finite repertoire of languages is an interesting observation, but it is not proof of a genetic constraint on possible forms, nor does it prove that such forms couldn't exist or couldn't be learned.

Contemporary theorists, besides Chomsky, working in the field of theories of psycholinguistics include George Lakoff, Steven Pinker, and Michael Tomasello.
(taken from: wikipedia)