Phrase structure rules

Phrase structure rules are rewrite rules that generate phrase structure(s). These have the general form of (i), where X is the name of the phrase and Y Z W defines its structure. Y, Z, and W are either phrases, and therefore must themselves occur to the left of the arrow in rules of this type, or non-phrasal (terminal) categories (such as Noun, Verb, or Determiner).

(i)    X	-&gt;	Y Z W ...

Example
the phrase structure rules in (ii) generate the phrase structure of the sentences in (iii).

(ii) a	 S	-&gt;	NP VP       b	 VP	-&gt;	V(NP) (PP) c	 NP	-&gt;	(Det) N      d	 PP	-&gt;	P NP

(Round Brackets indicate that a phrase is optional)

(iii) a	 John laughs b	 John eats an apple c	 The girl walks in the forest d	 The boy sends flowers to his mother

Thus the phrase structure rule in (ii)a characterizes a sentence (S) as the combination of an NP (the subject) and a VP (the predicate), i.e. as in (iv).

(iv) a	 [S [NP[N John]] [VP[V laughs] ] ] b	 [S [NP[N John]] [VP[V eats][NP[Det an][N apple]] ] ] c	 [S [NP[Det the][N girl]] [VP[V walks] [PP[P in] [NP[Det the][N forest]] ] ] ] d	 [S [NP[Det the][N boy]] [VP[V sends] [NP[N flowers]] [PP[P to][NP[Det his] [N mother] ] ] ] ]

The phrase structure rule in (ii)b gives the internal structure of the VP. According to this rule, a verbal phrase consists of a verb and, optionally, an NP and a PP. These last two constituents are further defined in phrase structure rules (iic/d).

Originally (cf. Chomsky 1957, 1965), phrase structure rules were meant to generate Deep-structures, which are converted into Surface structures by transformational rules. With the introduction of the Principles and Parameters framework (Cf. Stowell 1981, Chomsky 1986a), phrase structure rules have been eliminated from the theory of language as descriptive generalizations of what is better explained by deeper principles. Another term for phrase structure rules is rewrite rules. Also see X-bar theory.

Links
Utrecht Lexicon of Linguistics