Auxiliary verbwikipedia
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc.
auxiliary verbauxiliaryauxiliary verbsauxiliariesverbal auxiliarieshelper verbsfull verbauxiliary formsAVC

Do-support

do''-supportdo-supportinserted
– do is an auxiliary accompanying the main verb want, used here to form a question – see do-support.
Do-support (or do-insertion), in English grammar, is the use of the auxiliary verb do, including its inflected forms does and did, to form negated clauses and questions as well as other constructions in which subject–auxiliary inversion is required.

List of glossing abbreviations

abbreviatedglossing abbreviationglossing abbreviations
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.

Voice (grammar)

voicevoicesmiddle voice
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.
Specifically, it is made up of a form of the auxiliary verb to be and a past participle of the main verb.

Grammatical aspect

aspectgrammatical aspectaspectual
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.
Even languages that do not mark aspect morphologically or through auxiliary verbs, however, can convey such distinctions by the use of adverbs or other syntactic constructions.

English modal verbs

modal verbsshalldouble modal
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.
The modal verbs of English are a small class of auxiliary verbs used mostly to express modality (properties such as possibility, obligation, etc.).

Perfect (grammar)

perfectperfect aspectperfect tense
An example is the verb have in the sentence I have finished my lunch. Here, the main verb is finish, and the auxiliary have helps to express the perfect aspect.
(There are also additional forms such as future perfect, conditional perfect, and so on.) The formation of the perfect in English, using forms of an auxiliary verb (have) together with the past participle of the main verb, is paralleled in a number of other modern European languages.

Linguistic modality

modalitylinguistic modalitymodal
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.
Cross-linguistically, modality can be expressed by a variety of means, such as auxiliary verbs as in the examples (2) and (3), verbal morphology (mood) or adverbs.

Modal verb

modal verbmodalmodal auxiliaries
Modal verbs may or may not be classified as auxiliaries, depending on the language.
Like in other Romance languages, modal verbs in Italian (verbi modali or verbi servili) together with the preterite (passato remoto) possess the perfect form (passato prossimo), where they have the peculiarity to preferably inherit the auxiliary verb from the verb they hold.

Verb

verbverbsv.
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.
Grammatical tense is the use of auxiliary verbs or inflections to convey whether the action or state is before, simultaneous with, or after some reference point.

Going-to future

going togoing-to'' futureabout to
In French, for example, verbs such as devoir (have to), pouvoir (be able to), aller (be going to), vouloir (want), faire (make), and laisser (let), when used together with the infinitive of another verb, can be called semi-auxiliaries.
Like other modals, it is followed by the base infinitive of the main verb (compare with "ought to".) (An alternative description is that it uses the verb go in the progressive aspect, most commonly in present progressive form, serving as an auxiliary verb and having the to-infinitive phrase as its complement.

Uses of English verb forms

past progressivesimplefuture-in-the-past
| would 2 || future-in-the-past tense || After 1990, we would do that again.
Some forms of be and of certain other auxiliary verbs also have contracted forms (s, 're, 've, etc.).

Passive voice

passive voicepassivepassivization
| be 3 || passive voice || They were seen.
The passive forms in Nynorsk are restricted to only be accompanied by an auxiliary verb, which is not the case in Swedish and Danish.

Subject–auxiliary inversion

subject–auxiliary inversionsubject-auxiliary inversioninversion
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).
Subject–auxiliary inversion (also called subject–operator inversion) is a frequently occurring type of inversion in English, whereby a finite auxiliary verb – taken here to include finite forms of the copula be – appears to "invert" (change places) with the subject.

Light verb

light verblight verb constructionweak verb
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.
While light verbs are similar to auxiliary verbs regarding their meaning contribution to the clauses in which they appear, light verbs fail the diagnostics that identify auxiliary verbs and are therefore distinct from auxiliaries.

Future tense

futurefuture tenseFUT
| will 2 || future tense || The sun will rise tomorrow at 6:03.
In many cases, an auxiliary verb is used, as in English, where futurity is often indicated by the modal auxiliary will (or shall).

Grammatical tense

tensetensesgrammatical tense
An auxiliary verb (abbreviated ) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc. Auxiliary verbs usually accompany a main verb.
Multi-word tense constructions often involve auxiliary verbs or clitics.

English verbs

-edEnglishEnglish regular verbs
Most combinations of tense, aspect, mood and voice are expressed periphrastically, using constructions with auxiliary verbs.

Verb phrase ellipsis

verb phrase ellipsisVP-ellipsisshortened sentences
See the article on verb phrase ellipsis for examples.
In the types of VP-ellipsis considered here, which are features of English grammar, the elided VP must be a non-finite VP; it cannot be a finite VP. Further, the ellipsis must be introduced by an auxiliary verb (be, can, do, don't, could, have, may, might, shall, should, will, won't, would, etc.) or by the infinitive particle to.

Compound verb

compound verbcomplex predicatecompound
They are also to be distinguished from sequences of main plus auxiliary verbs.

Part of speech

part of speechparts of speechclosed class
The auxiliary verbs of a language form a closed class, i.e., there is a fixed, relatively small number of them.
Typical open classes found in English and many other languages are nouns, verbs (excluding auxiliary verbs, if these are regarded as a separate class), adjectives, adverbs and interjections.

Tense–aspect–mood

tense–aspect–moodTAMtense
Tense, aspect, and mood are usually indicated with separate invariant pre-verbal auxiliaries.

Predicate (grammar)

predicatepredicatespredication
Hence both do not qualify as separate predicates, but rather they form part of a predicate with another expression - usually with a full verb in the case of auxiliary verbs and usually with a noun in the case of light verbs.
These verb catenae generally contain a main verb and potentially one or more auxiliary verbs.

Affix

affixsuffixaffixes
Other languages, such as Latin, are synthetic, which means they tend to express functional meaning with affixes, not with auxiliary verbs.
(The niʔ here is an auxiliary, which can be ignored for explanatory purposes.)

Analytic language

analyticanalytic languageanalytical
These verb catenae are periphrastic forms of English, English being a relatively analytic language.

English auxiliaries and contractions

auxiliary verbcontractedauxiliaries
In English grammar, certain verb forms are classified as auxiliary verbs.