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Monday, January 28, 2008

Generative grammar

A generative grammar views linguistics combinatorially, through use of formal grammars. A generative grammar is defined as one that is fully explicit, in the sense that it consists of a set of rules by which it is possible to decide whether any given sentence is grammatical or not. In most cases, a generative grammar is capable of identifying as grammatical ("generating") an infinite number of strings, from a finite set of rules. This is obviously a requirement for a correct grammar of any natural human language.Generative grammars can be described and compared with the aid of the Chomsky hierarchy proposed by Noam Chomsky in the 1950s. This sets out a series of types of generative grammar of incresing power. The simplest is a finite state grammar, in which the rules are those of a Markov process of finite order; this is not a serious model for any natural human language, because all such languages allow the embedding of strings within strings in a hierarchical way. At the next level of complexity is a phrase structure grammar. On this view, a sentence is not a string of words, but rather a tree with subordinate and superordinate branches connected at nodes. The generating events are then hidden, hierarchically organised, and non-linear events, behind speech.Essentially, the tree model works something like this example, in which S is a sentence, D is a determiner, N a noun, V a verb, NP a noun phrase and VP a verb phrase:S / \ NP VP / \ / \ D N V NP / \ D NThe resulting sentence could be The dog ate the bone. Such a tree diagram is called a phrase marker. They can be represented more conveniently in a text form, (though the result is less easy to read): in this format the above sentence would be rendered as: [S[NP The dog] [VP ate [NP the bone />] or [S[NP D N] [VP V [NP D N />] A phrase marker only represents the grammatical structure of a sentence, not its semantic content. So the same phrase marker could equally well represent These elephants paraphrase the dinner. Consequently, part of the aim of generative grammar has to be to explain how native speakers "know" which sentences are meaningful as well as grammatical; this is the study of semantics as distinct from syntax or syntactics. However Chomsky argued that phrase structure grammars are also inadequate for describing natural languages, and it is necessary to proceed to a more abstract type of grammar, transformational grammar. When generative grammar was first described, it was widely hailed as a way of explaining the implicit set of rules a person "knows" when they know their native language and produce grammatical utterances in it. However Chomsky has repeatedly rejected that interpretation; according to him, the grammar of a language is a statement of what it is that a person has to know in order to recognise an utterance as grammatical, but not a hypothesis about the processes involved in either understanding or producing language. In any case the reality is that most native speakers would reject many sentences produced even by a phrase structure grammar. For example, although infinite embedding is allowed by the grammar, it is not accepted by either speakers or listeners, and the limit of acceptability is an empirical matter that varies between individuals, not something that can be easily captured in a formal grammar.. The influence of generative grammar in empirical psycholinguistics has reduced considerably.


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