PHRASE STRUCTURE (PS) GRAMMAR

There are three distinct periods of development in the theory of constituent structure.

1. Bloomfield only introduced the notion and explained it by means of examples.

2. His followers, notably, Eugene Nida, Rulon Wells, Zells Harris, formulated the principles of constituent analysis in greater detail.

3. Finally, the theory of constituent structure has been formalized and subjected to mathematical rigor by Chomsky and the other scholars and has been called Phrase Structure Grammar.

Once we start to use labels we have clearly departed from simple analysis and are undertaking analysis somewhat similar to traditional phrasing, the division of sentences into already established grammatical elements. This kind of analysis is called phrase structure grammar.

Phrase Structure Rules or Grammar considers sentence as linear sequence of elements. The aim is to identify these elements for their functions and class them appropriately. This is, therefore, better viewed as an alternative system to the IC analysis.

IC Analysis in Phrase Structure Grammar

The Sentence (The boys played with the girls) may be divided into two constituents: The boys and played with the girls. The first constituent may be categorized as NP (Noun Phrase) and the second as VP (Verb Phrase). This structure may be shown by a tree diagram. A phrase structure tree diagram will have all the nodes labelled. The above sentence may be analyzed as under.

The boys played with the girls.

A tree such as this represents an analysis of the sentence and may be described variously as an analysis tree, a phrase marker, or a parse tree, or is called simply an analysis or parse for the sentence. Now we shall take a long sentence. For example

A tall man with a gun followed the boy in a white uniform.

S

S P

NP VP

Det Adj Noun Prep Art N Verb Past Art N Prep Art Adj N

A tall man with a gun follow -ed the boy in a white uniform

Let us consider another sentence:

Old Sam sunbathed beside a stream

According to the PS model, the constituents of this sentence can be shown in the following manner.

1. S NP + VP (Old Sam + sunbathed beside a stream)

2. NP Mod (Adj) + N ( Old + Sam)

3. VP MV + PP (sunbathed + beside a stream)

4. VP Verb (sunbathed)

5. PP Prep. + NP (beside + a stream)

6. NP Art. + N (a + stream)

This can be shown in a tree-diagram

S

VP

NP PP

Mod N NP

Adj. V Prep. Art. N

Old Sam sunbathed beside a stream

A sentence thus consists of an NP (Noun Phrase) and a VP (Verb Phrase) or the Predicate Phrase. The Verb Phrase may include a verbal group and one or more Noun Phrase(s), Adjective Phrase(s) or Adverbial or Prepositional Phrases.

Chomsky presented three models of grammar in his revolutionizing book Syntactic Structures: Finite State Grammar, Phrase Structure Grammar, and Transformational Grammar. The first, the Finite State Grammar is the most basic and elementary and is full of inadequacies. The Phrase Structure Grammar takes us a long way in removing these shortcomings. The Transformational model is an extension of the PSG with addition of more complex type of rules.

Phrase Structure Rules

Phrase-structure rules are a way to describe a given languages 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 (or traditionally parts of speech).

Phrasal categories include the Noun Phrase, Verb Phrase, and Prepositional Phrase; Lexical categories include Noun, Verb, Adjective, Adverb, and many others. A grammar which uses phrase structure rules is called a phrase structure grammar.

Phrase structure rules are usually of the form A B C. meaning that the constituent A is separated into two sub constituents B and C. Some examples are:

1. S NP VP

2. NP Det. N

3. VP VP N

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

Some further categories are listed here: AP (adjective phrase), AdvP (adverb phrase), PP (prepositional phrase), etc. Applying the phrase structure rules in a neutral manner, it is possible to generate many proper sentences of English. But it is also quite possible that the rules generate syntactically correct but semantically nonsensical sentences. The following example sentence is notorious in this regard, since it is complete nonsense, even though it is syntactically correct:

Colorless green ideas sleep furiously

This sentence was constructed by 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. The tree for Chomsky's famous sentence can be rendered as follows:

S

NP

NP VP

A A N V Adv.

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.

Phrase structure grammar is itself hemmed in with limitations. It is efficient in explaining intra-sentence constituent elements, but cannot show inter-sentence relations such as declarative-interrogative, active-passive, and so on. It runs into difficulties when seeking to account for ambiguous sentences, ambiguity being more than a matter of immediate constituency as we can see in this ambiguous sentence.

Flying planes can be dangerous.

Similarly, PS rules cannot explain such discontinuous sentences as, He called me up, when the object is a pronoun and the discontinuous construction is obligatory.

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