XBar Theory Of Psg Essay Research Paper

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‘X-bar syntax as a theory of phrase structure grammar makes a significant contribution to both the descriptive and the explanatory adequacy of Linguistic Theory.’

The aim of a theory of language is to describe a speaker’s linguistic competence. (Class notes) In order for a grammar to be satisfactory it must satisfy two main conditions: descriptive adequacy and explanatory adequacy. A grammar that satisfies descriptive adequacy “describes the grammatical sentences of a language in such a way as to uncover deeper principles and rules which capture in a more satisfactory way the intuitions of the native speaker. A grammar which is formulated in accordance with the principles and conventions of a general i.e. universal linguistic theory with explanatory power is said to meet with explanatory adequacy.” (Class notes)

During the first half of the term we were introduced to a theory of phrase structure grammar (PSG) which includes two levels of categories: word-level (N V A P etc.) and phrase-level (NP AP VP PP etc.). However this is not a satisfactory method of classification because it does not include a description for a string of words that is neither a full phrase nor a word; therefore failing to satisfy descriptive adequacy. Furthermore it does not satisfy the condition of explanatory adequacy because it does not enable us to state general principles that are valid across different grammatical categories within a language i.e. category neutral. Moreover a grammar with two levels of categories is not powerful enough to state principles that hold true universally. In this essay I will demonstrate how the X-bar theory of phrase structure grammar contributes significantly to both the descriptive adequacy and explanatory adequacy of Linguistic Theory using examples from English and other languages.

Let us first examine why it is necessary to add a third intermediate grammatical category which is neither a full phrase nor a word. Evidence for this is found in the following phrase: the sultan of Brunei. Firstly we can prove that this phrase is a constituent by performing the following tests: 1) coordination – the sultan of Brunei and ruler of the empire. 2) Substituting the proform one – This sultan of Brunei is more handsome than the last one. Both of these tests prove that the constituent is sultan of Brunei and that it is smaller than a full phrase because in coordination and in substituting the proform one the Determiner ‘the’ is not included. In other words it is not correct to substitute the proform one and have *This sultan of Brunei is more handsome than the last this sultan of Brunei. (Class notes) Thus we see the need for an intermediate category. The best way of representing this category is by using bar notation i.e. N N’ and N’’. “The reason for this is that it captures the commonality in the categorial status by the use of the same category symbol and captures the difference in complexity between categories by the number of bars that accompany the symbol.” (Class notes) This is an example of how X-bar theory of grammar is able to capture descriptive adequacy more sufficiently than a two-category level PSG.

Another advantage of X-bar theory is that it enables us to capture formally a distinction between complements and adjuncts. (Class notes) This is advantageous because it can account for certain ambiguities. For example in PSG there is no satisfactory way of capturing the ambiguity in the following: A teacher of high moral principles. X-bar syntax enables us to capture the ambiguity very clearly in the following way:

A teacher of high moral principles vs.

A teacher of high moral principles

In the first tree structure the meaning of the sentence is the teacher has teaches high moral principles. In the second one the teacher is a person who has high moral principles. Thus the complement is closest to the head noun i.e. sister of the N and the adjunct is sister of the N’.

Another reason for which it is advantageous to distinguish between a complement and adjunct is that this distinction enables us to account for the distributional properties of PPs in terms of their status either as complements or as adjuncts. (Class notes) Firstly it is only possible to have one complement in a phrase: the governor of Texas vs. *the governor of Texas of California is ungrammatical. Secondly it is possible to have more than one adjunct e.g. the governor with grey hair with fat hands in the car. Thirdly the complement always precedes the adjunct. It is acceptable to have the governor with long eyelashes in the car but not *the governor in the car with long eyelashes. Fourthly when substituting the proform one it must refer to both the head and the complement. When asking “Which governor?” the answer the one with long eyelashes in the corner is acceptable but *the one of Texas is not. Finally it is only possible to coordinate either adjuncts or complements together not one of each as is

seen in the following examples: The vendor of fruits and vegetables

The vender with blond hair and blue eyes

*The vendor with blond hair and of vegetables.

In addition to enabling us to describe formally the occurrence of nominal postmodifiers X-bar syntax has also enables us to describe the occurrence of premodifiers. Just as in the case of postmodifiers premodifiers are optional. We can divide Nominal premodifiers into three different classes i.e. Determiners Attributes and Complements. Attributes are simply prenominal Adjuncts (Radford p. 197) and premodifier Complements perform the same function as postmodifier Complements. This can be seen by comparing the structures of the following phrases:

(1) A student of Linguistics at Reading vs.

(2) A Reading Linguistics student

In (1) above we see that the PP of Linguistics is a Complement (modifies N) whereas the PP at Reading is an Adjunct (modifies N-bar). By using the principle of structural symmetry we see that in (2) Linguistics is a Complement because it is the sister of the N student whereas Reading would be an Attribute because it is the sister (and daughter) of N’. It should be noted that Attributes could be either NPs or APs in which case they are called Adjectival premodifiers (Radford p. 216). For example the bracketed expression in the following expression is an AP: a [very boring] film is an Adjectival premodifier.

In the analysis of NPs I have shown the need for a third intermediate grammatical category which goes to show that it is descriptively more adequate than a theory that does not recognise a small nominal unit. We adopted bar notation to capture formally the relationship of three grammatical categories namely N’’ for the full phrase N’ for the intermediate phrase and N for the word level or the head of the phrase (Class notes). In order to prove that the X-Bar theory makes a contribution to explanatory adequacy we would need to show that it is possible to apply the same phrasal analysis to the other major grammatical categories i.e. VP AP PP and ADVP and then to other languages.

Before extending the phrasal analysis of the NP to the VP let us begin by recognising the need for a third intermediate category for VPs in the example eating a chocolate. This is shown by the fact that (1) only this unit can be preposed:

a) He might have been eating a chocolate.

b) Eating a chocolate he might have been.

c) *Been eating a chocolate he might have.

d) *Have been eating a chocolate he might.

And (2) some main verbs can only be combined with a verbal unit that consists of the verb and what follows it. As in I saw Mary close the curtains but not *I saw Mary be closing the curtains (Class notes).

Verbs are similar to NPs as they can combine with Complements and Adjuncts. This is shown in the structure below:

carve the turkey at my house on Christmas Day

Carve is the V or the head the NP the turkey is the Complement and it is closest to the head the PP at my house is an Adjunct and the PP on Christmas Day is an Adjunct as well.

The distinction between complement and adjunct helps to capture structural ambiguity in VPs just as it does in NPs. In the following example the PP on the boat can either be a Complement or an Adjunct:

They decided on the boat. vs. They decided on the boat.

In the first interpretation the decision took place on the boat whereas in the second they decided to purchase the boat (Class notes)

In addition “the distinction V complement and adjunct explains a number of distributional phenomena and therefore achieves better descriptive adequacy” (Class notes). For example He played football in Liverpool is an acceptable sentence but *He played in Liverpool football is not acceptable. This is because Complements normally precede Adjuncts.

It is clear from our analysis of the VP that introducing a third intermediate phrasal category as well as bar notation accounts for better descriptive adequacy. Furthermore we have seen that the system of phrasal analysis that applies for NPs can be extended to VPs which shows that the system has better explanatory adequacy. It is possible to go through all the phrasal categories and show that the X-bar theory holds true for all of them but due to the constraints on the length of this essay I will not do so. It is important however to state that due to crosscategorial symmetry i.e. all phrasal categories are analysed in the same way we are able to generalize the rules and state them in terms of the category variable X:

X” ? (Spec) ; X’

X’ ? YP ; X (Attribute rule optional)

X’ ? X’ ; YP (Adjunct rule optional)

X’ ? X ; YP (Complement Rule)

(Haegeman p.104)

There are three constraints on this theory: the Endocentricity Constraint the Modifier Maximality constraint and Category Neutrality Constraint. The Endocentricity Constraint states “the output of a rule must contain a category of the same type as the input category” (Class notes). The Modifier Maximality Constraint states that every non-head term must itself be a maximal projection of some category. This means that the sequence must be P-P’-P” where P” is the maximal projection of the category P. The Category Neutrality Constraint states that “all categorial rules must be formulated in terms of category variables” consequently eliminating all categorial rules (Class notes). These rules and constraints are said to be universals with the exception of languages differing along two parameters: “The configurationality parameter which determines whether the elements in the phrase are hierarchically organised in a fixed way or they are in a flat structure and The linear ordering parameter or the head first head last parameter” (Class notes).

Our analysis of phrases is now complete. The only category that has yet to be analysed according to X-bar analysis is S’. Let us consider the sentence I hope that the flight will arrive on time. We used to represent it:

the flight will arrive on time

There is a weakness in this analysis due to the following reasons: 1) it is a phrasal category but appears with only one bar instead of two. 2) The phrasal category S’ is not a projection of a lexical head. And 3) the main element of S’ is the lexical item of the Complementizer. Although this COMP is viewed as the head it has no corresponding maximal projection in the analysis above. We may revise the above in order that it may comply with X-bar syntax and avoid these problems in the following way:

that the flight will arrive on time

This is a better method of analysis because is complies with X-bar syntax and therefore leads to better explanatory power of the theory.

In order to illustrate the better explanatory power of X-bar syntax it is useful to apply the principles to other languages. The theory takes into account SOV languages such as English as well as to SVO languages such as Gujarati:

Mane phool khapechhe.

I flower want.

The semicolon that separates the constituents in the rule for example: X’? X;YP shows that the linear order is not fixed. This can also be illustrated in the following example from Lingala:

Muntu oyo alati bilamba ya rouge.

Person this wears clothes red(This person is wearing red clothes).

In conclusion X’ phrase structure grammar makes a significant contribution to descriptive and explanatory adequacy of Linguistic theory in a number of ways. It makes a contribution to descriptive adequacy in three ways. Firstly it simplifies grammar by adopting binary branching which in turn makes the learning of languages easier for children. Secondly it introduces a third intermediate phrasal category that allows us to distinguish between complements and adjuncts. Thirdly it introduces prime or bar notation which allows us to capture the distinction between categories formally i.e. using N” N’ and N.

X-bar theory adds to explanatory adequacy because it allows us to state general principles that apply across categories and are therefore category neutral. These principles are universals and apply across languages. In order to account for differences in languages the theory introduces two parameters. Due to the fact that this theory is simple and universal it helps us to explain the problem of learnablility therefore contributing to greater explanatory adequacy (Class notes).


Haegeman L. 1994. (2nd ed.) Introduction to Government and Binding Theory Oxford Blackwell.

Radford A. 1988 Transformational Grammar: A First Course. Cambridge CUP. (Chapter 4)