# X-bar

## English

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### Etymology

Pronunciation of its text representation: a letter X with overbar.

### Noun

X-bar

1. (grammar, X-bar theory) A phrase, or, equivalently, a node in a syntax tree, which consists either of: (1) an adjunct and another X-bar phrase, (2) a head, X, and an optional complement, or (3) a conjunction sandwiched between two other X-bars. The X is a "pro-letter" which can be substituted by letters such as N for noun, V for verb, P for preposition, I for inflectional, etc.
• 1988, Andrew Radford, chapter 7, in Transformational grammar: a first course, Cambridge, UK: Cambridge University Press, page 350:
For example, the fact that give must occur as the leftmost constituent of the V-bar containing it follows from two conditions. The first is a putatively universal linearisation (i.e. word-order) principle proposed by Stowell (1981, p. 68) which we might call the PERIPHERY PRINCIPLE: this can be outlined informally as in (33) below:
(33)      PERIPHERY PRINCIPLE
(33)      The head term of a Phrase appears at the periphery of X-bar
What (33) says is that the Head must be the leftmost or rightmost immediate constituent of X-bar.

#### Usage notes

An X-bar is denoted as ${\displaystyle {\bar {X}}}$ , or more commonly, as ${\displaystyle X'}$ .