Chapter 7 - Complementiser Phrases(62) CP
Op C'
C IP
Like other main clauses the complementiser position is empty and yet the null operator
must agree with something to ensure the correct interpretation of the clause. This then
is the trigger for the auxiliary inversion we see in yes–no main clauses. We end up
then with a very uniform analysis of interrogatives in English: they all have an
interrogative operator in the specifier position of the CP which agrees with the head. In
main clauses the head cannot contain a complementiser, so an auxiliary is moved to C
to enter into the agreement relationship. In subordinate clauses however,
complementisers can appear and so there is no need for auxiliary inversion:
(63) a CP b CP
wh C' wh C'
C IP C IP
e DP I' Q DP I'
I VP I VP
aux aux
A final issue we might mention in connection with this analysis concerns the
embedded clauses. If embedded questions can have complementisers as well as wh-
elements in their specifier positions, why do we never get them together?:
(64) a I never heard [Op if [they caught the burglar]]
b I never heard [who Q [they caught]]
c *I never heard [who if [they caught]]
This is a puzzle for which I have no real account. Apparently it is a very general
condition that a CP can contain either an overt operator or an overt complementiser.
We will see that this extends to other clauses too. Moreover, it appears not to be
violated by an auxiliary moving to C. The condition has been known as the Doubly
Filled COMP Filter since (1977) when it was introduced by Chomsky and Lasnik.
However, this stipulatory account has never been superseded by anything more
explanatory. I will therefore adopt the Doubly Filled COMP Filter as a condition on
the well-formedness of structures in lieu of a proper explanation:
(65) the Doubly Filled COMP Filter
no CP can have both an overt specifier and an overt complementiser
generated in C
This will have to suffice until we gain a better understanding of this phenomenon.