Definition of Auxiliary Verb

An auxiliary verb is a verb that adds 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 provides the main semantic content of the clause.^[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.

E.g

Below are some sentences that contain representative auxiliary verbs from English, German, and French, with the auxiliary verb marked in bold:

1. Do you want tea? – do is an auxiliary accompanying the main verb want, used here to form a question – see do-support.
2. He has given his all. – has is an auxiliary used in expressing the perfect aspect of give.
3. Das wurde mehrmals gesagt. – wurde 'became' is an auxiliary used to build the passive voice in German.

   That became many times said = 'That was said many times.'

4. Sie ist nach Hause gegangen. – ist 'is' is an auxiliary used with movement verbs to build the perfect                    tense/aspect in German.

She is to home gone = 'She went home/She has gone home.

5.  J'ai vu le soleil. – ai 'have' is an auxiliary used to build the perfect tense/aspect in French

     6.    have seen the sun = 'I have seen the sun/I saw the sun.'

7. Nous sommes arrivés. – sommes 'are' is an auxiliary used to build the passive voice in French.

We have arrived also as 'we are arriving'

These auxiliaries help express a question, show tense/aspect, or form passive voice. Auxiliaries like these typically appear with a full verb that carries the main semantic content of the clause.