In the early 1960s, the behaviorist approach to phonology then dominant in the USA was challenged by a new view, that of generative phonology, characterized by a mentalistic psychologizing outlook. Its chief proponents were Noam Chomsky and Morris Halle, who in 1968 produced their monumental book The Sound Pattern of English, which acted both as a foundation for their transformational-generative theory and an authoritative attempt to build a description of English Phonology on that theory.
1. A Grammar as a Machine
One might look upon a grammar as a machine which is able to produce or generative all and only the grammatical sentences of a language. As soon as such a machine is available for a particular language, the grammar of that language will automatically have been characterized. Research in transformational generative linguists is basically nothing more than an attempt to discover the properties of such a machine or grammar. One essential part of this machine is a phonological component in which are found all the phonological rules of a language; these rules will see to it that the machine does not generate empty syntactic structures, but rather that have a correct phonetic substance. The function of the phonological component is to bring about-step by step- a relationship between a syntactic surface and a phonetic surface structure (the output of the machine). The aim of generative phonology is twofold. Its first concern is to characterize the substance which is to be used for the specification of the pronunciation (i.e.;the phonetic representation of lexical elements and sentences). Second, a specific system is to be developed in order to connect syntactic surface structures with phonetic representations. The representation of lexical elements on both the phonetic and phonological levels is carried out by means of distinctive features,whereas the actual system is elaborated in terms of phonological rules. In addition, the generative phonologist will rely on the criterion of simplicity according to which the most elegant or most economical analysis will automatically be considered as the correct characterization of the phonological knoweldge of the native speech.
2. Generative Phonology
One of the most important tasks of the phonologist is to search for the correct input to the phonological to the phonological component.This means he will have to put forward an acceptable hypothesis about the actual form of the underlying representation. The underlying representation of many words will hardly differ from their actual pronunciation.
~Adopted from：R.E. Asher . 1994.The Encyclopedia of language and linguistics . Pergamon Press.