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X-bar theory is a theory of syntactic category formation. It embodies two independent claims: one, that phrases may contain intermediate constituents projected from a head X; and two, that this system of projected constituency may be common to more than one category (e.g., N, V, A, P, etc.). The letter X is used to signify an arbitrary lexical category (part of speech); when analyzing a specific utterance, specific categories are assigned. Thus, the X may become an N for noun, a V for verb, an A for adjective, or a P for preposition. The term ''X-bar'' is derived from the notation representing this structure. Certain structures are represented by X (an X with a bar over it). Because this may be difficult to typeset, this is often written as X′, using the prime symbol or with superscript numerals as exponents, e.g., X1. In English, however, this is still read as "X bar". The notation XP stands for ''X Phrase'', and is at the equivalent level of ''X-bar-bar'' (X with a double overbar), written X″ or X2, usually read aloud as ''X double bar''. X-bar theory was first proposed by Noam Chomsky (1970),〔Chomsky, Noam (1970). Remarks on nominalization. In: R. Jacobs and P. Rosenbaum (eds.) ''Reading in English Transformational Grammar'', 184-221. Waltham: Ginn.〕 building on Zellig Harris's 1951 (ch. 6) approach to categories, and further developed by Ray Jackendoff (1977). X-bar theory was incorporated into both transformational and nontransformational theories of syntax, including GB, GPSG, LFG, and HPSG. Recent work in the Minimalist Program has largely abandoned X-bar schemata in favor of Bare Phrase Structure approaches. ==Core concepts== There are three "syntax assembly" rules which form the basis of X-bar theory. These rules can be expressed in English, as immediate dominance rules for natural language (useful for example for programmers in the field of NLP—natural language processing), or visually as parse trees. All three representations are presented below. 1. An X Phrase consists of an optional specifier and an X-bar, in any order: XP → (specifier), X′
2. One kind of X-bar consists of an X-bar and an adjunct, in either order: (X′ → X′, adjunct) Not all XPs contain X′s with adjuncts, so this rewrite rule is "optional".
3. Another kind of X-bar consists of an X (the head of the phrase) and any number of complements (possibly zero), in any order: X′ → X, (complement...)
(a head-first and a head-final example showing one complement) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「X-bar theory」の詳細全文を読む スポンサード リンク
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