X-bar Theory - Core Concepts

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′ XP XP / \ or / \ spec X' X' spec

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".

X' X' / \ or / \ X' adjunct adjunct X'

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...) X' X' / \ or / \ X complement complement X

(a head-first and a head-final example showing one complement)

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