X-bar (adj./n.) ( or X′)

A system of GRAMMATICAL analysis developed in GENERATIVE LINGUISTICS as an alternative to traditional accounts of PHRASE STRUCTURE and LEXICAL CATEGORIES. It is argued both that the rules of phrase-structure grammar need to be more constrained (see constraint), and that more phrasal CATEGORIES need to be recognized. In particular, within the NOUN PHRASE, the need is felt to recognize intermediate categories larger than the noun but smaller than the phrase, e.g. very fast or very fast car in the phrase the very fast car. These intermediate categories, which have no status in previous phrase-structure models, are formally recognized in X-bar SYNTAX by a system of X-bars, each of which identifies a level of phrasal EXPANSION. Given a lexical category, X, X⁰ = ‘X with no bars’ (i.e. ‘zero-bar’, the category itself);  = X¹ = ‘X-bar’ = ‘X-single-bar’;  = X² = ‘X-double-bar’;  = X³ = ‘X-treble-bar’; and so on. For example, the following TREE illustrates two levels of expansion for N (‘N-bar’ and ‘N-double-bar’):

Each of the bar categories corresponding to X is known as a bar-projection of X. The value of recognizing intermediate categories in this way is widely agreed, but discussion continues about the number of categories which need to be recognized, and how far it is possible to generalize rules of category formation throughout a grammar.