Pic. 3. A Sample phrase structure of a sentence.

		S
	NP		VP
		mVG
		│	NG
det	H	mV	det	H
│	│	│	│	│
art	n	v	art	n
the	girl	chased	the	dog

If we start segmentation of the sentence ‘ The girl chased the dog ’, the first division produces a ‘noun phrase’ (NP) the girl and a ‘verb phrase’ (VP) chased the dog. The second division recognizes a verb ‘chased’ and another noun phrase ‘the dog’. The next division would produce combinations of a ‘determiner’ (det) and a noun (N) the + girl; the + dog. This is the ‘phrase structure’ of the sentence, and it can be displayed as a tree diagram:

The kind of representation of the phrase structure of a sentence is known a ‘phrase marker’ (P-marker). Phrase structures are also sometimes represented as labelled sets of brackets {[the/girl] [chase/ed] [the/dog]}, but these are more difficult to read, especially if a sentence is not simple – {[S [NP [DET_the] [N _girl]] [VP [V_chased] [NP[DET_the] [N_dog]]]}. The lines in Pic. 3 are considered to be the branches of an upside down tree.

The main disadvantage of this analysis is its extra-logical correctness – using the procedures above a researcher can find a general patterns of sentence constituency with every position filled with words belonging to some group type. However, a famous example of a grammatically correct sentence constructed by Noam Chomsky illustrates the necessity to include semantic rules of word combinability into the phrase structure analysis – Colorless green ideas sleep furiously can be diagrammed successfully as a phrase tree:

Pic. 4. A Noam Chomsky’ phrase structure of a sentence.

				S
	NP
		NP				VP
			AdvP
Adj		Adj		N		V		Adv
│		│		│		│		│
Colourless		green		ideas		sleep		furiously

Alternative approaches dispense with the idea of phrase structure rules and operate with the notion of schema instead. In this case phrase structures are not derived from strict and logical rules that combine word groups, but from the specification dependent on kind of semantic content of specific words that may appear in these schemes. One of the approaches is essentially equivalent to a system of phrase structure rules combined with a non-compositional semantic theory.

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