X-bar Theory
Chapter #6
0. INTRODUCTION
[The big book of poems with the blue cover] is on the table.
The structure our NP rule NP (D) (AdjP+) N (PP+) assigns to this is:
a flat structure: The PP of poems and the PP with the blue cover are on the same
level hierarchically; there is no distinction between them in terms of dominance
or c-command.
In other words they are “flat” with respect to the head word book.
X-bar theory
The name “X-bar theory” comes from the original mechanism for indicating
intermediate categories.
N' was written as an N with a bar over the letter.
This overbar or macron is the origin of the “bar” in the name of the theory.
“X” is a variable that stands for any category (N, Adj, V, P, etc.).
The following notations are all equivalent:
Phrasal level NP = N”= N''= N max
Intermediate level N' = N’
Word/Head level N = N°
The same is true of all other categories as well (e.g., PP = P”= P''= Pmax).
Since overbars are hard to type, even with Unicode fonts, most people use a
prime (') or apostrophe (‘) for the intermediate level and write the phrasal level
as NP (or more rarely, N'').
One-replacement is a process that targets the N' node:
One-replacement: Replace an N' node with one.
Without the intermediate N' node, we would have no
way of accounting for one-replacement or conjunction
facts. With N', explaining these sentences is easy, since
there is more structure in each phrase.
1.1 V-bar
There is a similar process to one-replacement in the syntax of
VPs. This is the process of do-so- (or did-so-) replacement.
Consider first the VP in the following sentence, which has both
an NP and a PP in it.
I [eat beans with a fork].
VP V’
V’ V' (PP) or V'( AdvP)
V’ V (NP)
The chef [eats beans] and [serves salads] with forks.
1.2 Adj-bar and Adv-bar
the [very [[bright blue] and [dull green]]] gown
In this NP, bright clearly modifies blue, and dull clearly modifies green. One
possible interpretation of this phrase (although not the only one) allows very to
modify both bright blue and dull green.
AdjP Adj’
Adj' (AdvP) Adj’
Adj’ Adj (PP)
1.3 P-bar
Gwen placed it [right [in the middle of the spaghetti sauce]].
In this example, prepositional phrases (in the middle of the
spaghetti sauce) that is modified by some other element: right
PP P’
P’ P' (PP) or (AdvP)
P’ P' (NP)
2. GENERALIZING THE RULES: THE X-BAR SCHEMA
The requirement that phrases are headed is called
endocentricity.
The only obligatory element in a phrase is the head.
3. COMPLEMENTS, ADJUNCTS, AND SPECIFIERS
the book [PP of poems] [PP with the glossy cover]
The two PPs in this tree are at different levels in the tree.
The lower PP1 is a sister to the head N (book), whereas
the higher PP2 is a sister to the N' dominating the head N
and PP1.
PP1 is introduced by the rule:
X’ X (WP)
PP2 is introduced by the higher-level rule:
X’ X’ (ZP)
An XP that is a sister to a head (N, V, A, or P) is called a complement.
PP1 is a complement.
XPs that are sisters to single bar levels (N', V', A', or P’) are daughters
of an X' are called adjuncts.
PP2 is an adjunct.
Adjuncts often have the feel of adverbials or obliques and are
typically optional additional information.
Adjunct: An XP that is a sister to a single bar level (N', V', A', or P') and a
daughter of a single bar level (N', V', A', or P').
Complement: An XP that is a sister to a head (N, V, A, P), and a daughter of
a single bar level (N', V', A', or P').
The rules that introduce these two kinds of XPs get special names:
Adjunct rule: X’ X' (ZP)
Complement rule: X’ X (WP)
3.1 Complements and Adjuncts in NPs
Consider the difference in meaning between the two NPs below:
1) the book of poems
2) the book with a red cover
the book [of poems] [with a red cover] [from Blackwell] [by Robert Burns]
head complement adjunct adjunct adjunct
