What does a phrase structure rule look like?

A typical rule is 'S goes to NP VP', meaning a sentence consists of a noun phrase followed by a verb phrase. Sets of such rules build up nested tree structures for whole sentences.

Are phrase structure rules still used?

In their original construction-specific form they have largely been replaced by general schemata like X-bar theory and by the operation Merge in minimalist syntax, though context-free style rules remain useful in computational and pedagogical settings.

Phrase Structure Rules

Phrase structure rules are rewrite rules that specify how a syntactic category can be expanded into a sequence of constituents, generating the hierarchical structure of sentences.

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Definition

A phrase structure rule is a rewrite rule of the form 'A goes to B C', stating that a constituent of category A can consist of constituents B and C, so that a set of such rules generates the well-formed hierarchical structures of a language.

Scope

This topic covers phrase structure (rewrite) rules: their form and function, the context-free grammars they define, their role in generating constituent structure together with the lexicon, and their eventual replacement by general schemata and operations. It does not cover the X-bar generalisation, constituency diagnostics, or movement, which are treated in sibling topics.

Core questions

How do rewrite rules generate hierarchical sentence structure?
What kind of grammar do phrase structure rules define?
How do phrase structure rules interact with the lexicon?
Why were construction-specific rules replaced by general principles?

Key concepts

rewrite rule
context-free grammar
phrase marker
recursion
lexical insertion
subcategorisation

Key theories

Phrase structure grammar: Chomsky's formalisation of constituent structure as a set of rewrite rules defining a context-free grammar that pairs sentences with hierarchical phrase markers.
Rules plus lexical insertion: The Aspects model in which phrase structure rules generate a categorial skeleton into which lexical items are inserted according to their subcategorisation properties.

History

Phrase structure rules were introduced in Chomsky (1957) as the base component of a generative grammar, drawing on the formal notion of rewrite systems. The Aspects model (1965) coupled them with a lexicon and lexical insertion. As the redundancy between construction-specific rules and general patterns became clear, the field moved toward the X-bar schema and, later, toward deriving structure from the operation Merge, largely eliminating language-particular phrase structure rules.

Debates

Adequacy of context-free phrase structure: Whether context-free phrase structure rules suffice to describe natural-language syntax, or whether transformations and additional mechanisms are required to capture displacement and long-distance dependencies.

Key figures

Noam Chomsky
Andrew Carnie
Emil Post

Seminal works

chomsky1957
chomsky1965
carnie2013

Frequently asked questions

What does a phrase structure rule look like?: A typical rule is 'S goes to NP VP', meaning a sentence consists of a noun phrase followed by a verb phrase. Sets of such rules build up nested tree structures for whole sentences.
Are phrase structure rules still used?: In their original construction-specific form they have largely been replaced by general schemata like X-bar theory and by the operation Merge in minimalist syntax, though context-free style rules remain useful in computational and pedagogical settings.