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:

Colorless green ideas sleep furiously.

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

Courtesy: http://en.wikipedia.org/wiki/Phrase_structure_rules