Avram Noam Chomsky (pronounced /ˌnoʊm ˈtʃɒmski/; born December 7, 1928) is an American linguist, philosopher,cognitive scientist, political activist, author, and lecturer . He is an Institute Professor and professor emeritus of linguistics at the Massachusetts Institute of Technology . Chomsky is well known in the academic and scientific community as one of the fathers of modern linguistics . Since the 1960s, he has become known more widely as a political dissident, an anarchist, and a libertarian socialist intellectual . Chomsky has been an active figure in contemporary philosophy . In the 1950s, Chomsky began developing his theory of generative grammar, which has undergone numerous revisions and has had a profound influence on linguistics . His approach to the study of language emphasizes "an innate set of linguistic principles shared by all humans" known as universal grammar, "the initial state of the language learner," and discovering an "account for linguistic variation via the most general possible mechanisms." He also established the Chomsky hierarchy, a classification of formal languages in terms of their generative power. In 1959, Chomsky published a widely influential review of B. F. Skinner's theoretical book Verbal Behavior, which was the first attempt by a behaviorist to provide a functional, operant analysis of language. In this review and other writings, Chomsky broadly and aggressively challenged the behaviorist approaches to studies of behavior dominant at the time, and contributed to the cognitive revolution in psychology. His naturalistic approach to the study of language has influenced the philosophy of language and mind. .