Current approaches to phrase structure derivation: X | theory
The problems with PS Rules led to the development (based on work by Chomsky, 1970) of a
different way of building up sentences, or derivations. This led to the development of X | theory,
and eventually to the way we do things at present, which makes use of a couple of principles,
interacting with parameters and the normal application of the syntactic operation Merge. We’ll go
through the derivation of a complex sentence, by way of illustration.
1. A:
What do you have to do to on Wednesday afternoons?
B:
Study linguistics.
B’s utterance illustrates that the simplest way of forming a phrase is to merge two words. By
merging study with linguistics, we form the phrase study linguistics.
What are the grammatical properties of the phrase in (1) B?
2. We are trying to study.
We are trying to study linguistics.
3. Linguistics is the subject of the future.
*Study linguistics is the subject of the future.
So study linguistics is a phrase with verblike, rather than nounlike properties; its grammatical
properties are determined by the verb study, and not by the noun linguistics. We can say that the
verb study is the head of the phrase study linguistics; and conversely that the phrase study
linguistics is a projection of the verb study.
4. [VP[Vstudy] [Nlinguistics] ]
5.
VP
V
study
N
linguistics
Structural relations:
V and N are sisters; V and N are daughters of the mother node VP, which immediately
dominates them. V is the head of its projection, VP. N is the complement of V.
Not all phrases consist of only two words, like study linguistics. But it would be useful to generalise
the idea that phrases are all formed by Merge (a syntactic operation). Merge combines two
categories to form a larger one.
1
6. A: What is Fred’s main aim in life?
B: To study linguistics.
The utterance in (6) B seems to be formed by merging the infinitival particle to with the VP study
linguistics. What would be the head of this structure? It is reasonable to guess that it would be the
infinitival to , which as we know occupies the I node. If this is indeed the case, then we would
expect the structure – an IP – to be distributed differently from the VP we saw in (5).
7. (a)
Everyone ought [IPto study linguistics].
(b)
*Everyone ought [VPstudy linguistics].
8. (a)
(b)
*Everyone should [IPto study linguistics].
Everyone should [VPstudy linguistics].
If we assume that study linguistics is a VP, and to study linguistics is an infinitival IP, then the
contrast shown in (7) and (8) above can be accounted for by suggesting that ought is a verb which
selects an (infinitival) IP complement, whereas should is a verb which selects a (tensed) VP
complement.
9.
[IP [Ito] [VP [Vstudy] [Nlinguistics] ] ]
10.
IP
I
to
VP
V
N
study
linguistics
The resulting IP is headed by to, and the verb phrase study linguistics is the complement of to. By
continuing to use the operation Merge in this fashion, we can build up more complex structures.
11.
12.
A:
What do you have in mind?
B:
Plans to study linguistics.
Plans to study linguistics are / *is often frustrated by the mafia.
2
(12) shows that the verb agrees with the plural noun plans, not the singular (despite its appearance)
noun linguistics. This indicates that the head of the phrase is the noun plans, and the structure is as
follows:
13.
NP
N
IP
I
VP
V
plans
14.
15.
to
N
study
linguistics
A:
What did the teachers object to?
B:
My plans to study linguistics.
DP
D
NP
N
IP
I
VP
V
my
plans
16.
A:
What did they take exception to?
B:
To my plans to study linguistics.
17.
study
linguistics
PP
P
to
to
N
DP
D
my
NP
N
IP
plans I
to
18.
VP
V
N
study
linguistics
A:
What do you think your father will do?
B:
Object to my plans to study linguistics.
3
19.
VP
V
PP
object P
to
DP
D
my
NP
N
IP
plans I
to
VP
V
N
study
linguistics
4. Intermediate Projections
20.
A:
What will your mother do?
B:
*Will object to my plans to study linguistics.
She will object to my plans to study linguistics.
Note that we can only use complete phrases to answer questions. So here we have a problem. If we
assume, as we have been doing up to now, that we merge an item with a structure and then project
the new item to be the head of the resulting tree, there should be no reason why Will object to my
plans to study linguistics should not be a complete phrase. But intuitively (and with regard to the
syntactic evidence re: using sentence fragments to answer questions) this is not the case. It seems
that auxiliaries (apart from infinitival to) must have a subject; this is also called the Extended
Projection Principle (it is a Principle, which means it is something true for ALL human languages
– and can therefore be understood as part of our genetic endowment). So the utterance will object to
my plans to study linguistics is ungrammatical because this principle is violated. What we have here
is an instance of an intermediate projection. It seems that the first utterance in (20) B is almost
a full IP, but not quite: it can’t really be a finite IP, because it has no subject. We call this an I | pronounced ‘I bar’.
4
21.
IP
I|
PRN
she
I
will
VP
V
PP
object P
to
DP
D
my
NP
N
IP
plans I
VP
to
V
N
study
linguistics
Notice that I is the head of a sentence, which is therefore an IP.
We do not use S any more, since there is no node in the tree to project such a category.
In a structure like (21), the pronominal subject she of the auxiliary will is said to be the specifier of
I. The VP object to my plans to study linguistics is the complement of I. X | -theory assumes that all
phrases have the following structure, where X is a variable across categories:
XP
maximal projection of X
X|
specifier
X
intermediate projection of X
complement
(head)
In a minimalist tree diagram, however, we only draw in the levels of projection which are actually
necessary for that sentence, missing out intermediate projections unless the head which is
projecting the phrase has a specifier (subject).
5
22.
23.
A:
What do you expect of your father?
B:
That he will object to my plans to study linguistics.
CP
C
IP
that
I|
PRN
he
I
will
VP
V
PP
object P
to
DP
D
my
NP
N
IP
plans I
to
VP
V
N
study
linguistics
Notice that C projects a CP; the notion of S | is also removed from this schema.
5. Some (more) terminology
A constituent is any sequence of items which can be traced exhaustively to a single node.
A constituent A is the complement of a head X iff A and X are sisters, and the mother of A is a
projection of X.
A constituent B is the specifier of a head X iff B is the sister of X| and the daughter of XP.
6. Why is this approach any better than PS Rules?
Learnability:
X | theory states:

all phrases have a head ( = the ENDOCENTRICITY CONSTRAINT)

the head is a zero projection (X 0)

complements combine (Merge) with X to project X |

adjuncts combine with X | to project another X |

the specifier combines with the topmost X | to project XP
6
In this way, we can reduce the formation of syntactic structures to a couple of principles interacting
with some parameters – especially the head parameter, which tells us whether a complement
precedes or follows its head – and the normal application of the syntactic operation Merge. The
child acquiring a language does not have to learn a whole, arbitrary, complicated set of rules.
S and S |:
As you know, all phrases must have a head, and all heads must project a phrase. This causes a
problem with S and S | , which :
-
are not phrases, as they have no head, and
-
are not lexical items, as they are made up of phrasal constituents (and we argued last time that
sentences could not be stored in the brain as whole units)
Under X | theory,
S is in fact a projection of I - it’s an IP.
S | is in fact a projection of C - it’s a CP.
There is no reason why IP and CP should be any different from the other phrases we have looked at
– they have heads which project, they can have intermediate projections, and they can take
specifiers and complements.
To summarise, although X | theory approaches to syntactic structure are not perfect, they more
closely approximate the major criteria for a theory of grammar: It is more universal, because it
captures commonalities between different phrases, and all languages seem to make use of it (subject
to certain areas of parametric variation), so it may have the status of a principle. This also increases
its explanatory adequacy; we do not have to learn about X | theory, because it is innate. And it
reduces the load on the language learner by making use of principles and parameters, rather than a
list of rules which have to be learnt and memorised.
7