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Phrase structure rules are a type of rewrite rule used to describe a given language's syntax, and are closely associated with the early stages of transformational grammar, being first proposed by Noam Chomsky in 1957.〔For general discussions of phrase structure rules, see for instance Borsley (1991:34ff.), Brinton (2000:165), Falk (2001:46ff.).〕 They are used to break down a natural language sentence into its constituent parts, also known as syntactic categories, including both lexical categories (parts of speech) and phrasal categories. A grammar that uses phrase structure rules is a type of phrase structure grammar. Phrase structure rules as they are commonly employed operate according to the constituency relation, and a grammar that employs phrase structure rules is therefore a ''constituency grammar''; as such, it stands in contrast to ''dependency grammars'', which are based on the dependency relation.〔Dependency grammars are associated above all with the work of Lucien Tesnière (1959).〕 ==Definition and examples== Phrase structure rules are usually of the following form: : meaning that the constituent is separated into the two subconstituents and . Some examples for English are as follows: : : : The first rule reads: An S (sentence) consists of an NP (noun phrase) followed by a VP (verb phrase). The second rule reads: A noun phrase consists of an optional Det (determiner) followed by an N (noun). The third rule means that an N (noun) can be preceded by an optional AP (adjective phrase) and followed by an optional PP (prepositional phrase). The round brackets indicate optional constituents. Beginning with the sentence symbol S, and applying the phrase structure rules successively, finally applying replacement rules to substitute actual words for the abstract symbols, it is possible to generate many proper sentences of English (or whichever language the rules are specified for). If the rules are correct, then any sentence produced in this way ought to be grammatically (syntactically) correct. It is also to be expected that the rules will generate syntactically correct but semantically nonsensical sentences, such as the following well-known example: ::Colorless green ideas sleep furiously This sentence was constructed by Noam Chomsky as an illustration that phrase structure rules are capable of generating syntactically correct but semantically incorrect sentences. Phrase structure rules break sentences down into their constituent parts. These constituents are often represented as tree structures. The tree for Chomsky's sentence can be rendered as follows: : A constituent is any word or combination of words that is dominated by a single node. Thus each individual word is a constituent. Further, the subject NP ''Colorless green ideas'', the minor NP ''green ideas'', and the VP ''sleep furiously'' are constituents. Phrase structure rules and the tree structures that are associated with them are a form of immediate constituent analysis. In transformational grammar, systems of phrase structure rules are supplemented by transformation rules, which act on an existing syntactic structure to produce a new one (performing such operations as negation, passivization, etc.). These transformations are not strictly required for generation, as the sentences they produce could be generated by a suitably expanded system of phrase structure rules alone, but transformations provide greater economy and enable significant relations between sentences to be reflected in the grammar. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phrase structure rules」の詳細全文を読む スポンサード リンク
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