Phrase structure rules

Phrase-structure rules are a way to describe a given language's syntax. They are used to break a natural language sentence down into its constituent parts (also known as syntactic categories) namely phrasal categories and lexical categories (aka parts of speech). Phrasal categories include the noun phrase, verb phrase, and prepositional phrase; lexical categories include noun, verb, adjective, adverb, and many others. Phrase structure rules were commonly used in transformational grammar (TGG), although they were not an invention of TGG; rather, early TGG's added to phrase structure rules (the most obvious example being transformations; see the page transformational grammar for an overview of the development of TGG.) A grammar which uses phrase structure rules is called a phrase structure grammar - except in computer science, where it is known as just a grammar, usually context-free.

Definition

Phrase structure rules are usually of the form

A \to B \quad C

, meaning that the constituent

A

is separated into the two subconstituents

B

and

C

Some examples correct inter alia for natural English language are:

: $S \to NP \quad VP$ : $NP \to Det \quad N1$ : $N1 \to (AP) \quad N1 \quad (PP)$

The first rule reads: An S consists of an NP followed by a VP. This means A sentence consists of a noun phrase followed by a verb phrase. The next one: ''A noun phrase consists of a determiner followed by a noun.

Further explanations of the constituents: S, Det, NP, VP, AP, PP

Associated with phrase structure rules is a famous example of a grammatically correct sentence. The sentence was constructed by Noam Chomsky as an illustration that syntactically but not semantically correct sentences are possible.

Colorless green ideas sleep furiously can be diagrammed as a phrase tree, as below:

where S represents a grammatical sentence. The theory of antisymmetry proposed in the early '90s by Richard Kayne is an attempt to derive phrase structure from a single axiom. A phrase tree can be represented by a ultrametric, see Mark D. Roberts http://arXiv.org/abs/cs.CL/9810012.

Alternative approaches

A number of theories of grammar dispense with the notion of phrase structure rules and operate with the notion of schema instead. 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 noncompositional semantic 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:

(NP(ADJ N) VP(V) AP(ADV))

And which would express the following conceptual content

X DOES Y IN THE MANNER OF Z

Though they are noncompositional, 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.

Name	Hakīm Abu'l-Qāsim Firdawsī Tūsī
Caption	Monument of Ferdowsi on his memorial square in Tehran. At the feet of the poet the heroes of his epic Shahnameh: future hero Zal and bird Simurgh.
Birthdate	940
Birthplace	Tus
Deathdate	1020
Deathplace	Tus
Occupation	Poet
Ethnicity	Persian
Genre	Persian poetry, Persian Mysticism, national epic
Movement	Poetry, Mysticism, Shia Islam, Metaphysics, ethics
Period	Ghaznavids

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Background

Links

Phrase structure rules

Definition

Alternative approaches

See also

Jason Schultz

External links

Ferdowsi

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