What Is Phrase Structure in English Grammar?

Phrase structure grammar is a type of generative grammar in which constituent structures are represented by phrase structure rules or rewrite rules. Some of the different versions of phrase structure grammar (including head-driven phrase structure grammar) are considered in examples and observations below.

A phrase structure (or constituent) functions as the base component in the classic form of transformational grammar introduced by Noam Chomsky in the late 1950s. Since the mid-1980s, however, lexical-function grammar (LFG), categorial grammar (CG), and head-driven phrase structure grammar (HPSG) "have developed into well-worked-out alternatives to transformational grammar"

Examples and Observations

• "The underlying structure of a sentence or a phrase is sometimes called its phrase structure or phrase marker. . . . Phrase-structure rules provide us with the underlying syntactic structure of sentences we both produce and comprehend. . . .
• "There are different types of phrase-structure grammar. Context-free grammars contain only rules that are not specified for particular contexts, whereas context-sensitive grammars can have rules that can only be applied in certain circumstances. In a context-free rule, the left-hand symbol can always be rewritten by the right-hand one regardless of the context in which it occurs. For example, the writing of a verb in its singular or plural form depends on the context of the preceding noun phrase."
  

Rewrite Rules

"The idea of a PSG [phrase structure grammar] is simple. We first note what syntactic categories appear to exist in a given language, and what different internal structures each of these can have. Then, for each such structure, we write a rule that displays that structure. So, for example, an English sentence typically consists of a noun phrase followed by a verb phrase (as in My sister bought a car), and we, therefore, write a phrase-structure rule as follows:

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English Language Sentence Structure

By Richard Nordquist

S→NP VP

This says that a sentence may consist of a noun phrase followed by a verb phrase. . . . We continue in this way until we have a rule for every structure in the language.
"Now the set of rules can be used to generate sentences. Starting with S (for 'sentence'), we apply some suitable rule to tell us what units the sentence consists of, and then to each of those units we apply a further rule to tell us what units it consists of, and so on."

"A phrase structure grammar consists of a set of ordered rules known as rewrite rules, which are applied stepwise. A rewrite rule has a single symbol on the left and one or more symbols on the right:

A→B+C
C→D

More than one symbol on the right constitutes a string. The arrow is read as 'is rewritten as,' 'has as its constituents,' 'consists of,' or 'is expanded as.' The plus sign is read as 'followed by,' but it is often omitted. The rule may also be depicted in the form of a tree diagram...
"The phrase structure rules also allow for choices. The optional choices are indicated with parentheses:

A→(B)C

This rule reads that A is expanded as optionally B and obligatorily C. In every rewrite rule, at least one element must be obligatory. There may also be mutually exclusive choices of elements in a string; these are indicated with curly braces: 

A→{B,C}

This rule states that if you choose B, you can't choose C, but you must choose one—either B or C, but not both. Whether the mutually exclusive items are written on one line separated by commas or on separate lines does not matter, as long as they occur within braces."

Head-Driven Phrase Structure Grammar (HPSG)

• "Head-driven phrase structure grammar (HPSG) has evolved as a synthesis of ideas from a number of theoretical sources, including generalized phrase structure grammar (GPSG), categorial grammar, and formal theories of data structure representation . . .. HPSG uses a fundamental theoretical strategy made familiar by GPSG: the enumeration of a class of objects, corresponding to expressions of some natural language, and a set of constraints whose interaction enforces the appropriate covariation of formal properties reflecting the dependencies that any grammar of that language must capture."
• "A head-driven phrase structure grammar of some language defines the set of signs (form/meaning/correspondences) which that language comprises. The formal entities that model signs in HPSG are complex objects called feature structures, whose form is limited by a set of constraints--some universal and some language parochial. The interaction of these constraints defines the grammatical structure of each such sign and the morphosyntactic dependencies which hold between its subcomponents. Given a specific set of such constraints, and a lexicon providing at least one feature structure description for each word in the language, an infinite number of signs is recursively characterized."
  

Sources

• Borsley and Börjars, Non-Transformational Syntax, 2011.
• Laurel J. Brinton, The Structure of Modern English: A Linguistic Introduction. John Benjamins, 2000
• R.L. Trask, Language, and Linguistics: The Key Concepts, 2nd ed., edited by Peter Stockwell. Routledge, 2007
• Trevor A. Harley, The Psychology of Language: From Data to Theory, 4th edition. Psychology Press, 2014
• Georgia M. Green and Robert D. Levine, Introduction to Studies in Contemporary Phrase Structure Grammar. Cambridge University Press, 1999