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Reference.org
Phrase structure rules
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<p>Phrase structure rules are a type of <a href="/facts/Rewrite_rule/9PHlnnnJ">rewrite rule</a> used to describe a given language's <a href="/facts/Syntax/6PxSV98p">syntax</a> and are closely associated with the early stages of <a href="/facts/Transformational_grammar/vqIyVYdP">transformational grammar</a>, proposed by <a href="/facts/Noam_Chomsky/3rtpzlER">Noam Chomsky</a> in 1957. They are used to break down a natural <a href="/facts/Language/IRcTok2q">language</a> sentence into its constituent parts, also known as <a href="/facts/Syntactic_category/5KqpcMEk">syntactic categories</a>, including both lexical categories (<a href="/facts/Part_of_speech/WbQ89MHX">parts of speech</a>) and <a href="/facts/Phrase/mbnD0ksH">phrasal</a> categories. A grammar that uses phrase structure rules is a type of <a href="/facts/Phrase_structure_grammar/SbzQXRFM">phrase structure grammar</a>. Phrase structure rules as they are commonly employed operate according to the <a href="/facts/Constituent_(linguistics)/7eIG0Ap3">constituency</a> relation, and a grammar that employs phrase structure rules is therefore a <a href="/facts/Phrase_structure_grammar/SbzQXRFM"><i>constituency grammar</i></a>; as such, it stands in contrast to <a href="/facts/Dependency_grammar/cWnwcCM0"><i>dependency grammars</i></a>, which are based on the <a href="/facts/Government_(linguistics)/dyh4gmGw">dependency</a> relation. </p>