List of auxiliaries in English Diagnostics for identifying auxiliary verbs in English

Traits across languages[edit]

Auxiliary verbs typically help express grammatical tense, aspect, mood, and voice. They generally appear together with an infinitive. The auxiliary is said to "help" the infinitive. The auxiliary verbs of a language form a closed class, i.e., there is a fixed, relatively small number of them.^[8]
Widely acknowledged verbs that can serve as auxiliaries in English and many related^{[clarification needed]} languages are the equivalents of be to express passive voice, and have (and sometimes be) to express perfect aspect or past time reference.^[9]
In some treatments, the copula be is classed as an auxiliary even though it does not "help" another verb, e.g.,
The bird is in the tree. – is serves as a copula with a predicative expression not containing any other verb.
Definitions of auxiliary verbs are not always consistent across languages, or even among authors discussing the same language. Modal verbs may or may not be classified as auxiliaries, depending on the language. In the case of English, verbs are often identified as auxiliaries based on their grammatical behavior, as described below. In some cases, verbs that function similarly to auxiliaries, but are not considered full members of that class (perhaps because they carry some independent lexical information), are called semi-auxiliaries. 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.^[10] There has also been a study on auxiliary verb constructions in Dravidian languages

n English[edit]

Main article: English auxiliaries and contractions
The following sections consider auxiliary verbs in English. They list auxiliary verbs, then present the diagnostics that motivate this special class (subject-auxiliary inversion and negation with not). The modal verbs are included in this class, due to their behavior with respect to these diagnostics.