Unit 6: Mainly About Verbs
6.4 Auxiliary "do"
DO is sometimes referred to as a DUMMY element since its main function is the purely grammatical one of marking the VP in interrogative and negative clauses. Such marking is necessary only where the VP has simple aspect. Compare:
14a. He is sleeping.
14b. Is he sleeping?
14c. He is not sleeping.
15a. He smiled.
15b. Did he smile? (* Smiled he?)
15c. He didn't smile. (* He smiled not.)
In the examples in (15), did fills the slot filled by the auxiliary is in (14). The starred forms under (15) were perfectly acceptable at earlier stages of the language; you will find many examples of such structures in Shakespeare's writing.
Dummy do is also used in short answers, as in 16, and in TAG QUESTIONS, such as 17, which invite the listener's agreement:
16a. Did he go? Yes, he did.
16b. Who cares? I do/His mother does.
17a. It was raining hard, wasn't it?
17b. He went, didn't he?
Do also has an emphatic function, marked by underlining in written English:
18. Reading does take up a lot of time.
