X-bar theory

In <a href="/facts/Linguistics/oQuamvf2">linguistics</a>, X-bar theory is a model of phrase structure and a theory of syntactic category formation that proposes a universal schema for how phrases are organized. It suggests that all phrases share a common underlying structure, regardless of their specific category (<a href="/facts/Noun_phrase/mmz3tJt9">noun phrase</a>, <a href="/facts/Verb_phrase/nfJ5hbY8">verb phrase</a>, etc.). This structure, known as the X-bar schema, is based on the idea that every phrase (XP, X phrase) has a <a href="/facts/Head_(linguistics)/aBTxhyr9">head</a>, which determines the type (<a href="/facts/Syntactic_category/5KqpcMEk">syntactic category</a>) of the phrase (X). 
The theory was first proposed by <a href="/facts/Noam_Chomsky/3rtpzlER">Noam Chomsky</a> in 1970 reformulating the ideas of <a href="/facts/Zellig_Harris/fpvaf8FF">Zellig Harris</a> (1951), and further developed by <a href="/facts/Ray_Jackendoff/T9rKpW9q">Ray Jackendoff</a> (1974, 1977a, 1977b), along the lines of the theory of <a href="/facts/Generative_grammar/Pm1AMX5U">generative grammar</a> put forth in the 1950s by Chomsky. It aimed to simplify and generalize the rules of grammar, addressing limitations of earlier phrase structure models. X-bar theory was an important step forward because it simplified the description of sentence structure. Earlier approaches needed many <a href="/facts/Phrase_structure_rules/B867agmG">phrase structure rules</a>, which went against the idea of a simple, underlying system for language. X-bar theory offered a more elegant and economical solution, aligned with the thesis of <a href="/facts/Generative_grammar/Pm1AMX5U">generative grammar</a>.
X-bar theory was incorporated into both transformational and nontransformational theories of syntax, including <a href="/facts/Government_and_binding_theory/2DTpSetS">government and binding theory</a> (GB), <a href="/facts/Generalized_phrase_structure_grammar/RuMYkqI2">generalized phrase structure grammar</a> (GPSG), <a href="/facts/Lexical-functional_grammar/UqAfrL1G">lexical-functional grammar</a> (LFG), and <a href="/facts/Head-driven_phrase_structure_grammar/MW1TXsca">head-driven phrase structure grammar</a> (HPSG). Although recent work in the <a href="/facts/Minimalist_program/K6YhIlAz">minimalist program</a> has largely abandoned X-bar schema in favor of <a href="/facts/Bare_phrase_structure/K6YhIlAz">bare phrase structure</a> approaches, the theory's central assumptions are still valid in different forms and terms in many theories of minimalist syntax.

X-bar theory open-in-new

X-bar theory