Auxiliary verbs are so called because they help to form the various tenses, moods, and voicesof other verbs. The principal ones are be, do, and have.
Be is used with other verbs to form continuous tenses and the passive voice:
She is reading a magazine.
We were talking to them for ages.
England were beaten by Germany in the final.
Have is used to make perfect tenses:
The judge had asked her to speak up.
In two years, we will have established community gardens.
Do is used:
He did look tired.
to make questions:
Do you want a coffee?
to form negative statements or questions:
I don’t like meat.
Didn’t he know how to play football?
There is a further set of auxiliary verbs known as modal verbs or modal auxiliary verbs. These combine with other verbs to express necessity, possibility, intention, or ability. The modal auxiliary verbs are must, shall, will, should, would, ought (to), can, could, may, and might. For example:
You must act promptly.
Can you speak Spanish?
I would go if I could afford it.
He said he might reconsider his decision.
I ought to visit my family.
We should get to London before midday.
May I come in?