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Auxiliary Verbs

Auxiliary verbs form a closed class

As well as the huge number of lexical verbs, there is a limited number of so-called auxiliary verbs. As the membership is restricted and as it is not easy to add new ones, auxiliary verbs (like numerals, determiners, pronouns, prepositions and conjunctions) form a closed word class.

Auxiliary verbs have a grammatical function

Auxiliary verbs have a mainly grammatical function. Consider the following example of the use of a present participle.

the boy is crying

In this utterance the word crying is the lexical verb. Its base form would, of course, be cry (see Lexical Verbs). But consider the word is. We know that this is a verb, as it is derived from the verb be. In this context, however, the word does not appear to convey any specific meaning of its own. It appears to have a largely grammatical function, serving to signal the present participle in its association with the –ing morpheme. The word is in this context is not, therefore, a lexical verb but it is classified as an auxiliary verb. There is a sense in which it has been added to the main verb (lexical verb) in order to construct the verb phrase (is crying). Auxiliary verbs are typically used in this way with main verbs to construct verb phrases. All auxiliary verbs are placed before the main verb.

There are two types of auxiliary verb: (1) primary auxiliaries, and (2) modal auxiliaries.

Primary auxiliaries

The main primary auxiliary verbs are be, have and do. Like lexical verbs, they can be inflected, e.g.


I am going

I was going

he is singing

he was singing

they are writing

they were writing


I have gone

I had gone

he has played

he had played

we have written

we had written


we do go there quite a lot

we did go there quite a lot

do you want one?

did you want one?

please do not shout

Modal auxiliaries

We have seen elsewhere (see Verbs) that modal verbs characteristically denote the attitude or mood of the speaker, expressing stance meanings related to obligation, necessity, possibility, and similar. There are a number of distinguishing characteristics (Biber, Conrad, Leech, 2002:174):

  • act only as auxiliary verbs in verb phrases (e.g. you might cry)
  • their form does not vary (e.g. it may happen, not *it mays happen)
  • precede the negative particle in ‘not negation’ (e.g. they could not go)
  • precede the subject in ‘yes-no questions’ (e.g. will he write?)
  • take the bare infinitive in verb phrases (e.g. she can call, not *she can to call)

Central modal verbs

There are nine central modals in English:

  1. can
  2. could
  3. shall
  4. should
  5. will
  6. would
  7. may
  8. might
  9. must

As they can only function as auxiliary verbs, they are placed before a main verb. For example:

Serena should win the match easily

we might take a career break

surely they must see how silly it is?

Semi-modal verbs

For the most part, semi-modals are multi-word combinations that function in the same way as modals. Examples include:

  • be going to (e.g. she is going to call me)
  • be about to (e.g. they were about to go)
  • have (got) to (e.g. Bill has got to go; Bill has to go)
  • (had) better (e.g. we had better leave quickly; we better leave quickly)
  • be supposed to (e.g. the door is supposed to work)
  • used to (e.g. Hasan used to live here)
  • ought to (e.g. we really ought to send a card)

Semi-modals can sometimes be substituted with a single central modal verb, e.g.

they ought to buy a gift – they should buy a gift

Carl has got to pay it today – Carl must pay it today

Sandra is going to come – Sandra will come

The semi-modals be going to and be about to are one of the means of marking future time in English.


Biber, D., Conrad, S. and Leech, G. (2002) Student Grammar of Spoken English Harlow: Longman.