5.3.2 The nature of the aspectual morpheme
Finally, presuming the clause to be finite, some element will have to bear the tense morpheme. As the verb cannot do this, the relevant dummy auxiliary will be inserted into the tense position: have in the presence of en and be in the presence of ing. In (167c) there is the extra complication that there are two aspectual morphemes as well as the tense morpheme. In this case the verb moves to the lowest aspectual morpheme, ing, and an inserted auxiliary will bear the other morphemes, be for the perfective and have for the tense:
6.2.1 Inserting auxiliaries into I
In the previous chapter, we introduced the idea that dummy auxiliaries are inserted into a structure when the verb is unable to support a bound morpheme. Consider what happens with regard to a bound inflectional element such as the present tense morpheme s:
The use of have and be as supporting auxiliaries is therefore associated with the appearance of the aspectual morphemes whose presence necessitates the use of the auxiliary by ‘tying-up’ the verb so that it cannot support any other morpheme. The use of the dummy auxiliary do however, is a little different as it is not associated with the appearance of any aspectual morpheme and indeed cannot be used in the presence of one:
Accepting this, we can account for the insertion of dummy do. The verb will not be able to move to inflection without violating the HMC. Apparently in English, the negative is not the sort of verbal element that can support tense and hence the only option available is to insert an auxiliary. As there is no aspectual morpheme to deem otherwise, the inserted auxiliary will be do:
6.2.4 Movement to tense and I
As we mentioned previously, the negative element is not so accommodating and it refuses to give up its place below the finite inflection and above the verb. Thus in this case the verb cannot support the inflection and the dummy auxiliary has to be inserted:
As we can see, a yes–no question involving a main verb moving to the C position is ungrammatical and instead of the main verb moving to C what happens is that the dummy auxiliary do is inserted into the tense position, and from there it moves to C, via I. Of course, this is readily accounted for if main verbs do not move to I, as is the standard assumption. If they are never in I they cannot move to C without violating the head movement constraint. But we argued that main verbs can move to I and so it is not readily apparent why they cannot move to C. We will put this issue to one side until we have discussed the facts about I-to-C movement more fully. For the time being, then, we will concentrate on I-to-C movement as it involves auxiliary verbs.
7.3.5 Subject questions
It seems that for some reason, to which we return shortly, main verbs cannot move to C. So when a wh-element moves to the specifier of CP and it requires some element in the C position to agree with, the dummy auxiliary is used and hence we get do-insertion. However, when the subject is the focus of the question, there is no do-insertion indicating that nothing has to move to C. If this is a general condition then it suggests that no element moves from I to C in subject questions and hence that (67c) is not correct. Opinions differ as to the correctness of (67a) or (b), but obviously both are problematic for the straightforward analysis of interrogatives.
7.3.5 Subject questions
We have seen restrictions like this before. The adverb, for example must be above the verb and the negation must be above the verb but below the tense. It seems that the verb must be below the subject and hence when the subject is in spec IP the verb can be no higher than I. However, when the subject moves to spec CP the verb can move to C and still remain lower than the subject. When the verb cannot move from I to C there is no choice other than to insert the auxiliary do. However, it appears that the dummy auxiliary is not enough by itself to provide the wh-element with something to agree with, thus the auxiliary must be inserted in to tense and move from there to I and from there to C to provide enough semantic content to support the agreement. The verb stays behind in the VP: