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.
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
Related topics
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.