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Phrase structure rules are a type of
rewrite rule In mathematics, computer science, and logic, rewriting covers a wide range of methods of replacing subterms of a well-formed formula, formula with other terms. Such methods may be achieved by rewriting systems (also known as rewrite systems, rewr ...
used to describe a given language's
syntax In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentence (linguistics), sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence st ...

syntax
and are closely associated with the early stages of
transformational grammar In linguistics, transformational grammar (TG) or transformational-generative grammar (TGG) is part of the theory of generative grammar, especially of natural languages. It considers grammar to be a system of rules that generate exactly those combin ...
, proposed by
Noam Chomsky Avram Noam Chomsky (born December 7, 1928) is an American public intellectual: a linguist, philosopher, cognitive scientist, historian, social critic, and political activist. Sometimes called "the father of modern linguistics", Chomsky is ...

Noam Chomsky
in 1957. They are used to break down a natural
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...

language
sentence into its constituent parts, also known as
syntactic categories A syntactic category is a syntactic unit that theories of syntax assume. Word classes, largely corresponding to traditional parts of speech (e.g. noun, verb, preposition, etc.), are syntactic categories. In phrase structure grammars, the ''phrasal c ...
, including both lexical categories (
parts of speech In grammar, a part of speech or part-of-speech (Abbreviation, abbreviated as POS or PoS, also known as word class or grammatical category) is a category of words (or, more generally, of lexical items) that have similar grammar, grammatical properti ...
) and
phrasal
phrasal
categories. A grammar that uses phrase structure rules is a type of
phrase structure grammar The term phrase structure grammar was originally introduced by Noam Chomsky as the term for formal grammar, grammar studied previously by Emil Post and Axel Thue (Post canonical systems). Some authors, however, reserve the term for more restricted ...
. Phrase structure rules as they are commonly employed operate according to the
constituency An electoral district, also known as an election district, legislative district, voting district, constituency, riding, ward, division, or (election) precinct is a subdivision of a larger state (a country A country is a distinct part o ...
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.


Definition and examples

Phrase structure rules are usually of the following form: :A \to B \quad C meaning that the
constituent Constituent or constituency may refer to: Politics * An individual voting, voter within an electoral district, state, community, or organization * Advocacy group or constituency * Constituent assembly * Constituencies of Namibia Other meanings * ...
A is separated into the two subconstituents B and C. Some examples for English are as follows: :S -> NP \quad VP :NP -> (Det) \quad N1 :N1 -> (AP) \quad N1 \quad (PP) The first rule reads: A S ( sentence) consists of a NP (
noun phrase In linguistics, a noun phrase, or nominal (phrase), is a phrase that has a noun or pronoun as its head (linguistics), head or performs the same Grammar, grammatical function as a noun. Noun phrases are very common linguistic typology, cross-lingui ...
) followed by a VP (
verb phrase In linguistics, a verb phrase (VP) is a syntax, syntactic unit composed of a verb and its argument (linguistics), arguments except the subject (grammar), subject of an independent clause or coordinate clause. Thus, in the sentence ''A fat man quic ...
). The second rule reads: A noun phrase consists of an optional Det (
determiner A determiner, also called determinative (list of glossing abbreviations, abbreviated ), is a word, phrase, or affix that occurs together with a noun or noun phrase and generally serves to express the reference of that noun or noun phrase in the ...
) followed by a N (noun). The third rule means that a N (noun) can be preceded by an optional AP (
adjective phrase An adjective phrase (or adjectival phrase) is a phrase whose Head (linguistics), head is an adjective. Almost any grammar or syntax textbook or dictionary of linguistics terminology defines the adjective phrase in a similar way, e.g. Kesner Bland (1 ...
) and followed by an optional PP (
prepositional phrase An adpositional phrase, in linguistics, is a syntactic category that includes ''prepositional phrases'', ''postpositional phrases'', and ''circumpositional phrases''. Adpositional phrases contain an adposition (preposition, postposition, or circ ...
). 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 Semantics (from grc, wikt:σημαντικός, σημαντικός ''sēmantikós'', "significant") is the study of reference, Meaning (philosophy), meaning, or truth. The term can be used to refer to subfields of several distinct discipline ...
nonsensical sentences, such as the following well-known example: ::
Colorless green ideas sleep furiously ''Colorless green ideas sleep furiously'' is a sentence composed by Noam Chomsky in his 1957 book ''Syntactic Structures'' as an example of a sentence (linguistics), sentence that is grammatically Well-formedness, well-formed, but semantically N ...
This sentence was constructed by
Noam Chomsky Avram Noam Chomsky (born December 7, 1928) is an American public intellectual: a linguist, philosopher, cognitive scientist, historian, social critic, and political activist. Sometimes called "the father of modern linguistics", Chomsky is ...

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 (
dendrogram A dendrogram is a diagram A diagram is a symbolic Depiction, representation of information using Visualization (graphics), visualization techniques. Diagrams have been used since prehistoric times on Cave painting, walls of caves, but be ...
s). The tree for Chomsky's sentence can be rendered as follows: : 300px, Colorless green ideas sleep furiously. 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 In linguistics, transformational grammar (TG) or transformational-generative grammar (TGG) is part of the theory of generative grammar, especially of natural languages. It considers grammar to be a system of rules that generate exactly those combin ...
, 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 In logic, negation, also called the logical complement, is an operation (mathematics), operation that takes a Proposition (mathematics), proposition P to another proposition "not P", written \neg P, \mathord P or \overline. It is interpreted ...
, 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.


Top down

An important aspect of phrase structure rules is that they view sentence structure from the top down. The category on the left of the arrow is a greater constituent and the immediate constituents to the right of the arrow are lesser constituents. Constituents are successively broken down into their parts as one moves down a list of phrase structure rules for a given sentence. This top-down view of sentence structure stands in contrast to much work done in modern theoretical syntax. In
Minimalism In visual arts The visual arts are Art#Forms, genres, media, and styles, art forms such as painting, drawing, printmaking, sculpture, ceramics (art), ceramics, photography, video, filmmaking, design, crafts and architecture. Many artistic ...
for instance, sentence structure is generated from the bottom up. The operation Merge merges smaller constituents to create greater constituents until the greatest constituent (i.e. the sentence) is reached. In this regard, theoretical syntax abandoned phrase structure rules long ago, although their importance for
computational linguistics Computational linguistics is an Interdisciplinarity, interdisciplinary field concerned with the computational modelling of natural language, as well as the study of appropriate computational approaches to linguistic questions. In general, comput ...
seems to remain intact.


Alternative approaches


Constituency vs. dependency

Phrase structure rules as they are commonly employed result in a view of sentence structure that is ''constituency-based''. Thus, grammars that employ phrase structure rules are ''constituency grammars'' (=
phrase structure grammar The term phrase structure grammar was originally introduced by Noam Chomsky as the term for formal grammar, grammar studied previously by Emil Post and Axel Thue (Post canonical systems). Some authors, however, reserve the term for more restricted ...
s), as opposed to ''
dependency grammar Dependency grammar (DG) is a class of modern Grammar, grammatical theories that are all based on the dependency relation (as opposed to the ''constituency relation'' of Phrase structure grammar, phrase structure) and that can be traced back prima ...
s'', which view sentence structure as ''dependency-based''. What this means is that for phrase structure rules to be applicable at all, one has to pursue a constituency-based understanding of sentence structure. The constituency relation is a one-to-one-or-more correspondence. For every word in a sentence, there is at least one node in the syntactic structure that corresponds to that word. The dependency relation, in contrast, is a one-to-one relation; for every word in the sentence, there is exactly one node in the syntactic structure that corresponds to that word. The distinction is illustrated with the following trees: : The constituency tree on the left could be generated by phrase structure rules. The sentence S is broken down into smaller and smaller constituent parts. The dependency tree on the right could not, in contrast, be generated by phrase structure rules (at least not as they are commonly interpreted).


Representational grammars

A number of representational phrase structure theories of grammar never acknowledged phrase structure rules, but have pursued instead an understanding of sentence structure in terms the notion of
schema The word schema comes from the Greek word ('), which means ''shape'', or more generally, ''plan''. The plural is ('). In English, both ''schemas'' and ''schemata'' are used as plural forms. Schema may refer to: Science and technology * SCHEMA ...
. Here phrase structures are not derived from rules that combine words, but from the specification or instantiation of syntactic schemata or configurations, often expressing some kind of semantic content independently of the specific words that appear in them. This approach is essentially equivalent to a system of phrase structure rules combined with a non compositional
semantic Semantics (from grc, wikt:σημαντικός, σημαντικός ''sēmantikós'', "significant") is the study of reference, Meaning (philosophy), meaning, or truth. The term can be used to refer to subfields of several distinct discipline ...
theory, since grammatical formalisms based on rewriting rules are generally equivalent in power to those based on substitution into schemata. So in this type of approach, instead of being derived from the application of a number of phrase structure rules, the sentence ''Colorless green ideas sleep furiously'' would be generated by filling the words into the slots of a schema having the following structure: :: P[ADJ_NVP[V.html"_;"title="DJ_N.html"_;"title="P[ADJ_N">P[ADJ_NVP[V">DJ_N.html"_;"title="P[ADJ_N">P[ADJ_NVP[VAP[ADV.html" ;"title="DJ_N">P[ADJ_NVP[V.html" ;"title="DJ_N.html" ;"title="P[ADJ N">P[ADJ NVP[V">DJ_N.html" ;"title="P[ADJ N">P[ADJ NVP[VAP[ADV">DJ_N">P[ADJ_NVP[V.html" ;"title="DJ_N.html" ;"title="P[ADJ N">P[ADJ NVP[V">DJ_N.html" ;"title="P[ADJ N">P[ADJ NVP[VAP[ADV And which would express the following conceptual content: ::X DOES Y IN THE MANNER OF Z Though they are non-compositional, such models are monotonic. This approach is highly developed within Construction grammar and has had some influence in Head-Driven Phrase Structure Grammar and Lexical Functional Grammar,Concerning Lexical Functional Grammar, see Bresnan (2001). the latter two clearly qualifying as phrase structure grammars.


See also


Notes


References

{{refbegin, 2 *Ágel, V., Ludwig Eichinger, Hans-Werner Eroms, Peter Hellwig, Hans Heringer, and Hennig Lobin (eds.) 2003/6
Dependency and Valency: An International Handbook of Contemporary Research
Berlin: Walter de Gruyter. *Borsley, R. 1991. Syntactic theory: A unified approach. London: Edward Arnold. *Bresnan, Joan 2001. Lexical Functional Syntax. *Brinton, L. 2000
The structure of modern English
Amsterdam: John Benjamins Publishing Company. *Carnie, A. 2013
Syntax: A Generative Introduction
3rd edition. Oxford: Blackwell Publishing. *Chomsky, N. 1957. Syntactic Structures. The Hague/Paris: Mouton. *Chomsky, N. 1995. The Minimalist Program. Cambridge, Mass.: The MIT Press. *Falk, Y. 2001. Lexical-Functional Grammar: An introduction to parallel constraint-based syntax. Stanford, CA: CSLI Publications. *Goldberg, A. 2006
Constructions at Work: The Nature of Generalization in Language
Oxford University Press. *Pollard, C. and I. Sag 1994
Head-driven phrase structure grammar
Chicago: University of Chicago Press. *Tesnière, L. 1959. Éleménts de syntaxe structurale. Paris: Klincksieck. Grammar frameworks Generative syntax Syntactic theories Phrases Syntax Syntactic categories Syntactic relationships