Lexicalfunctional

Lexicalfunctional grammar, commonly abbreviated as LFG, is a theory of syntactic structure in linguistics developed in the late 20th century by Joan Bresnan and Ronald Kaplan. It presents a modular view of grammar that separates two parallel representations: a hierarchical constituent structure (c-structure) that reflects surface word order, and a flat, functional structure (f-structure) that encodes grammatical relations and feature information such as subject, object, tense, number, and case.

In LFG, the lexicon plays a central role by supplying lexical entries with subcategorization frames and functional specifications that determine how a word contributes to both c-structure and f-structure. The c-structure is built from phrase-structure rules and represents the actual string of words, while the f-structure provides a language-independent analysis of syntactic functions and feature values. The two representations are linked by a set of functional equations and projection constraints that map elements from the surface structure to their corresponding functional roles.

This approach offers several advantages. By decoupling form from function, LFG accommodates cross-linguistic variation and complex morphologies, supports flexible word order, and provides a straightforward framework for describing long-distance dependencies and optional constituents. It also lends itself to computational implementation, with parsers and grammars that separately handle constituency and functional mappings.

Since its introduction, LFG has influenced theoretical syntax and been adopted in computational linguistics to build grammars for multiple languages. Notable contributors include Bresnan and Kaplan, with ongoing work and extensions exploring its applicability to diverse linguistic phenomena and NLP tasks.