Avram Noam Chomsky (born December 7, 1928) is an American intellectual, philosopher, linguist, political activist, and social critic. Sometimes called "the father of modern linguistics", Chomsky is also a major figure in analytic philosophy and one of the founders of the field of cognitive science. He is a laureate professor of linguistics at the University of Arizona and an institute professor em Chomsky is commonly credited with inventing transformational-generative grammar, but his original contribution was considered modest when he first published his theory. In his 1955 dissertation and his 1957 textbook Syntactic Structures, he presented recent developments in the analysis formulated by Zellig Harris, who was Chomsky's PhD supervisor, and by Charles F. Hockett. Their method derives from the work of the structural linguist Louis Hjelmslev, who introduced algorithmic grammar to general linguistics. Based on this rule-based notation of grammars, Chomsky grouped logically possible phrase-structure grammar types into a series of four nested subsets and increasingly complex types, together known as the Chomsky hierarchy. This classification remains relevant to formal language theory and theoretical computer science, especially programming language theory, compiler construction, and automata theory. Chomsky's Syntactic Structures became, beyond generative linguistics as such, a catalyst for connecting what in Hjelmslev's and Jespersen's time was the beginnings of structural linguistics, which has become cognitive linguistics. Chomsky's status as the "most-quoted living author" is credited to his political writings, which vastly outnumber his writings on linguistics. Chomsky biographer Wolfgang B. Sperlich characterizes him as "one of the most notable contemporary champions of the people"; journalist John Pilger has described him as a "genuine people's hero; an inspiration for struggles all over the world for that basic decency known as freedom. To a lot of people in the margins—activists and movements—he's unfailingly supportive." Arundhati Roy has called him "one of the greatest, most radical public thinkers of our time", and Edward Said thought him "one of the most significant challengers of unjust power and delusions". Fred Halliday has said that by the start of the 21st century Chomsky had become a "guru" for the world's anti-capitalist and anti-imperialist movements. The propaganda model of media criticism that he and Herman developed has been widely accepted in radical media critiques and adopted to some level in mainstream criticism of the media,…

Formal grammar A formal grammar says how to form an expression or a word, that is valid in a formal language. In the 1950s, Noam Chomsky classified formal grammars, into what is known as Chomsky hierarchy today: There are four different types of such grammars, numbered 0 to 3. Higher level grammars are stricter than lower level grammars.