Interrogative CPsNo other complementiser can do this:
(58) a I don’t know [if and when to stand up]
b she wondered [if or not to pack the bags]
Finally consider the fact that the word whether was used in Old English to introduce
yes–no questions in main clauses:
(59) hwœðer ge nu secan gold on treowum
whether you now seek gold in trees
‘do you now seek gold in trees’
Yet Old English did not have main sentences that started with complementisers,
indicating that whether never was a complementiser even in former stages of the
language.
But if whether is not a complementiser, what is it? It differs in one very large way
from wh-elements and that is while wh-elements move out of a clause whether does
not seem to. Wh-elements are all moved to the spec CP from some position inside the
IP and therefore they are always associated with a ‘gap’ in the clause, filled, of course,
by a trace:
(60) a [CP who 1 did [IP you think I met t 1 ]]
b [CP who 1 did [IP he say t 1 likes tennis]]
c [CP where 1 did [IP you put the anti-tank missiles t 1 ]]
But whether is not linked to any position inside the IP from which it has moved. This,
I think, is understandable in terms of the functions of wh-elements. Most wh-elements
are used in wh-questions and their function is to mark the clause as an interrogative
and to indicate what the focus of the question is. (60a), for example is a question about
the object, which is the position from which the wh-element derives. As we said, the
function of whether is to mark a yes–no question and these questions focus on the truth
of the sentence rather than on any particular piece of information it may carry. For this
reason, then, whether does not need to hold a position in the clause, it merely indicates
the clause’s question status. We may assume therefore that whether is a wh-element
that is generated directly in the specifier of CP as a general interrogative operator. As
it appears in embedded contexts, it will be accompanied by an interrogative
complementiser Q with which it agrees:
(61) CP
whether C'
C IP
Q
What about main clause yes–no questions? Obviously in Modern English, whether
is not allowed to appear in main clauses. But we might suppose that something appears
in the same position in main clause interrogatives. This is clearly an operator like
whether, only phonologically null. Standardly, null operators are denoted by Op: