English grammar - Roger Berry 2012
A6.1 Auxiliaries
A6 Auxiliaries and the verb phrase
Section A. Introduction
In A5 we looked at verb forms. But, as with nouns and noun phrases, there is a larger unit that we need to recognise when looking at the organisation of clauses and sentences: the verb phrase. Similar to noun phrases, verb phrases consist of a verb and all the other words that ’go with it’. But in this case, the words that can ’go with’ verbs are limited to the auxiliaries (with the possible exception of adverb particles - see B7), and the length of verb phrases is strictly limited.
The major difference between tense and aspect (see B5 for their meanings) is that tense is only morphological in nature (i.e. it affects the form of words), while aspect is formed with the use of extra words - the auxiliaries.
A6.1 Auxiliaries
Auxiliaries are a closed word class. They can be divided into two sub-classes:
□ modal auxiliaries: will, would, shall, should, may, might, can, could, must. They are discussed at length in B6
□ primary auxiliaries: be, have, do.
The primary auxiliaries are also main verbs, and like them (but unlike the modals) have a full set of verb forms, as described in A5. The use of do as a primary auxiliary in the formation of negatives is dealt with in A7. The rest of this section is concerned with the use of be and have in the construction of verb phrases involving aspect and the passive.