In the 1950s the school of linguistic thought known as transformational-generative grammar received wide acclaim through the works of Noam Chomsky. Chomsky postulated a syntactic base of language (called deep structure), which consists of a series of phrase-structure rewrite rules, i.e., a series of (possibly universal) rules that generates the underlying phrase-structure of a sentence, and a series of rules (called transformations) that act upon the phrase-structure to form more complex sentences. The end result of a transformational-generative grammar is a surface structure that, after the addition of words and pronunciations, is identical to an actual sentence of a language. All languages have the same deep structure, but they differ from each other in surface structure because of the application of different rules for transformations, pronunciation, and word insertion. Another important distinction made in transformational-generative grammar is the difference between language competence (the subconscious control of a linguistic system) and language performance (the speaker's actual use of language). Although the first work done in transformational-generative grammar was syntactic, later studies have applied the theory to the phonological and semantic components of language.
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