Noam Chomsky is the foremost linguistic theorist of the post–World War II era, an important contributor to philosophical debates, and a notable radical activist. His influence is felt in many other fields, however, most notably, perhaps, in the area of cognitive studies.

Chomsky's main achievement was to distinguish linguistic competence from its manifestations in performance and to characterize competence as a system of explicit rules for the construction and interpretation of sentences. Indeed, this achievement provided a model for investigations, in this and other cognitive domains, that replaced then-dominant models based on the notion of analogy and oriented to the causal explanation of behavior.

The competence of individuals to use their language is constituted, on Chomsky's account, by their (tacit) knowledge of a formal grammar (or system of rules); their linguistic performance, involving the deployment of such knowledge, may be influenced by a...