A Synopsis of X Bar Theory: Prepared For University Students

A summary of X bar theory for university students

  1. Introduction to X-bar theory

             Phrase Structure Grammar was based on the assumption that there are two types of syntactic categories (word-level and phrase-level categories) that together make up the sentence of a natural language (Ex: English). However, this claim was not supported by enough evidence. As a reaction, the extended standard theory or which is known as X bar syntax came to prove that there must be three categories in the hierarchical representation of the sentence. In more expressive words, a category that is smaller than phrasal categories and bigger than lexical ones should be inserted to adequately describe the syntactic components of the sentence.

Consider the following table:

X Word levelX-bar levelX Phrase level
  1. Why a new category?

Consider the following phrase:

  1. Ex: a teacher of linguistics

              Linguists argue that while (teacher) is a nominal phrase teacher of linguistics is also a nominal phrase. The reason why linguists consider this syntactic unit as an in-between category is as matter of fact explained by a bunch of evidence.

Distributional evidence

              This sort of evidence states that this generalized category can take independently a certain distribution within the sentence for instance:

  1. Ex: She became teacher of linguistics


            The second evidence elucidates that this sort of nominal phrase can only be joined with another nominal phrase that has the same syntactic attributes (since it has been mentioned in the previous chapter that only equivalent phrases can be coordinated).

  1. Ex: she was a [teacher of linguistics] and [great person]


  1. Ex: The new [teacher of linguistics] is better than the last one

To clarify this, teacher of linguistics can only be replaced by one, which in a sense shows that [teacher of linguistics] can stand by itself as a nominal phrase. Therefore, it would be impossible to do this:

The [teacher] of linguistics was the one who I met yesterday.

So basically, the idea that must be grabbed from the above illustrations is that a new category should be inserted in-between the lexical and the phrasal category. Therefore the situation has changed to be (three syntactic categories).

  • Complements and adjuncts

  1. The teacher of linguistics


  1. The teacher of linguistics with smiley face

= N  + N  (PP)(ADJUNCT)



              As it can be seen from the box which is under (Ex: F) above, there are two PPs, but one functions as COMPL whereas the other functions as an ADJUNCT. So, what would be the difference between COPML and ADJUNCT?

The answer is that COMPL is specifying what the teacher does whereas ADJUNCT doesn’t:

  • He is a teacher of linguistics
  • He is teaching linguistics
  • He is a teacher with smiley face
  • He is teaching smiley face

One can notice again from the box (f) above that ADJUNCT and COMPL have different levels, and that ADJUNCT is a sister and daughter of N’ whereas COMPL is a daughter of N’ but a  sister of N

For more clarification let’s consider the following phrases:

The teacher of mathThe teacher of math from RabatThe teacher


The teacher from Rabat







= N  + N  (PP)(ADJUNCT)







= N  + N (PP)(ADJUNCT)


To conclude, the three modifiers (DET, COMPL, and ADJUNCT) can actually generate the following rules:

  1. N”= (D) +N’ [DET rule]
  2. N’=   N’ + N’ (PP) [ADJUNCT rule, optional]
  3. N’=   N+ (PP) [COMPL rule]

Note: the brackets have to do with the optionality of the constituent

Taking into consideration the rules above (adjunct can exist at the level of N’), it could be possible to generate phrases with more than adjuncts.

  • The teacher [with blue eyes] [with chubby face] [with flabby abdomen]

But can’t construct syntactic structures like:

  • The teacher [of linguistics] [of Arabic] [of geography]

And this logically leads us to another piece of evidence that claims that only elements of the same syntactic attributes can be coordinated:

  1. Ex:
  • The teacher of linguistics and geography
  • The man with blue eyes and with chubby face
  • *The teacher of English and with blue eyes (false)

Basically, adjuncts and complements are attached at different levels, ADJUNCTS are sisters of N’. Therefore, they can be attached at the level of N’, whereas COMPLS are sisters of N, they can be attached at the level of N. It’s safe to conclude that only elements of the same level can be conjoined.

The semantic evidence

The semantic evidence states that each category determines a semantic feature

  1. Ex: Ahmed is [a teacher of linguistics]


             Therefore, and as it is noticed from syntactic division. ‘’A teacher’’ or ‘’a teacher of linguistics’’ are two semantic features that can strictly be attributed to Ahmed.

  1. Nominal pre-modifier

           There are three types of nominal pre-modifiers namely: determiner, complement N, and attribute N. But, before plunging into the process of distinguishing COMPLs (N) from attributes (N), it would so much helpful to re-mention again that the section of post-modifiers above was concluded with the following rules:


N”=  (D) +N’ [DET rule]

N’=   N’ + N’ (PP) [ADJUNCT rule, optional]

N’=   N+ (PP) [COMPL rule]

            The reason to re-mention these rules is to show that ADJUNCTS (PP) are just as the same as ATTRIBUTES (NS) and that COMPLS (PP) is just the same as COPMLS (NP)

Let’s consider this example

  1. Ex: a university English student

= NP (university)+N’

= NP (English)+N

             The order of constituents in (g) is the only syntactic possibility that sounds more correct, because one can’t have an order such as an English university student (it sounds a bit more ambiguous because we don’t know whether English modify university or student). Therefore, we assume that the possible order is ‘’a university English student’’ and that ATTRIBUTE (NP) comes before COMPL (NP).

Let’s consider the upcoming examples:

  1. A biology student
  2. A university biology student

The thing here is that both biology student and university student are both N’ phrasal category, but at different levels and to justify this, let’s look at coordination:

  1. A biology and chemistry student
  2. A university and college student
  3. *A university and chemistry student (false)

To sum up, just as adjuncts PP are similar to attributes NP, they share some structural features, COMPLs PP are similar to COMPLs (NP)

  1. The student of French
  2. The French student
  3. The student of Ibn Zohr
  4. The Ibn Zohr student
  1. Adjectival pre-modifier

Adjective phrase (AP) is another type of attributes; it takes after the attributive NP in the sense that they have the same order:

  1. The Morocco football player
  2. The Moroccan football player

Let’s consider this example:

  1. A white intelligent Moroccan boy

 = AP+N’

 = AP+N’

 = AP+N’

N’ =N

From the above analysis, it can be noticed that AP has the same syntactic level just as N’ level (that is to say a sister of N’), this structural feature allows us to say AP is as the same as adjuncts PP in that they can be stacked:

  1. Tall black Moroccan boy
  2. Tall Moroccan black boy
  3. Moroccan tall black boy
  4. Black tall Moroccan boy

Concluding by the rules:

The Rules of nominal post-modifiers


  • N’=N’+PP    (rule of adjunct)
  • N’=N+PP     (rule of complement)


The Rules of pre-modifiers


  • N”= det+N’  (DET determiner rule )
  • N’=NP+N     (NP complement rule)
  • N’=AP+N’    (attribute rule )



  • Chomsky, N. (1980). On Binding. Linguistic Inquiry 11:1-46.
  • Haegeman, L. (1994). Introduction to Government and Binding theory. Blackwell. Oxford.

This one is highly recommended for students of linguistics and theoretical syntax:

  • Radford, A. (1997). Syntax: A Minimalist Introduction. Cambridge: Cambridge University Press. 




Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top