English Grammar - Auxiliary verb

Auxiliary verb

An auxiliary verb is a verb used to add functional or grammatical meaning to the clause in which it appears – for example, to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb, the main verb providing the main semantic content of the clause in which it appears.^[1] An example is the verb have in the sentence I have finished my dinner – here the main verb is finish, and the auxiliary have helps to express the perfect aspect. Some sentences contain a chain of two or more auxiliary verbs. Auxiliary verbs are also called helping verbs, helper verbs, or (verbal) auxiliaries. They may be glossed with the abbreviation AUX.

a. Do you want tea? – do is an auxiliary accompanying the main verb want, used here to form a question – see do-support.

b. He has given his all. – has is an auxiliary used in expressing the perfect aspect of give.

A list of auxiliaries in English

A list of verbs that (can) function as auxiliaries in English is as follows:^[9]

be (am, are, is, was, were, being), can, could, dare*, do (does, did), have (has, had, having), may, might, must, need*, ought*, shall, should, will, would

* The status of dare, need (not), and ought (to) is debatable;^[10] and the use of these verbs as auxiliaries can vary across dialects of English.

If the negative forms can't, don't, won't, etc. are viewed as separate verbs (and not as contractions), then the number of auxiliaries increases. The verbs do and have can also function as full verbs or as light verbs, which can be a source of confusion about their status. The modal verbs (can, could, may, might, must, shall, should, will, would, and dare, need and ought when included) form a subclass of auxiliary verbs. Modal verbs are defective insofar as they cannot be inflected, nor do they appear as gerunds, infinitives, or participles.

The following table summarizes the auxiliary verbs in standard English and the meaning contribution to the clauses in which they appear. Many auxiliary verbs are listed more than once in the table based upon discernible differences in use.

Auxiliary verb	Meaning contribution	Example
be1	copula (= linking verb)	She is the boss.
be2	progressive aspect	He is sleeping.
be3	passive voice	They were seen.
can1	deontic modality	I can swim.
can2	epistemic modality	Such things can help.
could1	deontic modality	I could swim.
could2	epistemic modality	That could help.
do	do-support/emphasis	You did not understand.
have	perfect aspect	They have understood.
may1	deontic modality	May I stay?
may2	epistemic modality	That may take place.
might	epistemic modality	We might give it a try.
must1	deontic modality	You must not mock me.
must2	epistemic modality	It must have rained.
shall	deontic modality	You shall not pass.
should1	deontic modality	You should listen.
should2	epistemic modality	That should help.
will	epistemic modality	We will eat pie.
would	epistemic modality	Nothing would accomplish that.

Deontic modality expresses an ability, necessity, or obligation that is associated with an agent subject. Epistemic modality expresses the speaker's assessment of reality or likelihood of reality. Distinguishing between the two types of modality can be difficult, since many sentences contain a modal verb that allows both interpretations.

Diagnostics for identifying auxiliary verbs in English

The verbs listed in the previous section can be classified as auxiliaries based upon two diagnostics: they allow subject–auxiliary inversion (the type of inversion used to form questions etc.) and (equivalently) they can take not as a postdependent (a dependent that follows its head). The following examples illustrate the extent to which subject–auxiliary inversion can occur with an auxiliary verb but not with a full verb:^[11]

a. He was working today.

b. Was he working today? - Auxiliary verb was allows subject–auxiliary inversion.

a. He worked today.

b. *Worked he today? - Full verb worked does not allow subject–auxiliary inversion.

a. She can see it.

b. Can she see it? - Auxiliary verb can allows subject–auxiliary inversion.

a. She sees it.

b. *Sees she it? - Full verb sees does not allow subject–auxiliary inversion.

(The asterisk * is the means commonly used in linguistics to indicate that the example is grammatically unacceptable.) The following examples illustrate that the negation not can appear as a postdependent of a finite auxiliary verb, but not as a postdependent of a finite full verb:^[12]

a. Sam would try that.

b. Sam would not try that. - The negation not appears as a postdependent of the finite auxiliary would.

a. Sam tried that.

b. *Sam tried not that. - The negation not cannot appear as a postdependent of the finite full verb tried.

a. Tom could help.

b. Tom could not help. - The negation not appears as a postdependent of the finite auxiliary could.

a. Tom helped.

b. *Tom helped not. - The negation not cannot appear as a postdependent of the finite full verb helped.

A third diagnostic that can be used for identifying auxiliary verbs is verb phrase ellipsis. Auxiliary verbs can introduce verb phrase ellipsis, but main verbs cannot.^{[citation needed]} See the article on verb phrase ellipsis for examples.

Note that these criteria lead to the copula be being considered an auxiliary (it undergoes inversion and takes postdependent not, e.g. Is she the boss?, She is not the boss). However, if one defines auxiliary verb as a verb that somehow "helps" another verb, then the copula be is not an auxiliary, because it appears without another verb. The literature on auxiliary verbs is somewhat inconsistent in this area.^[13]