The verbs be (is, am, are, was and were), have and do are called auxiliary verbs when they are used with ordinary verbs
to make tenses, passive forms, questions and negatives.
The verbs can, could, may, might, will, would,
shall, should, must and ought are called modal verbs. Modal verbs are
used before ordinary verbs and express ideas such as permission, possibility,
certainty and necessity. Need and dare are also sometimes used like modal
verbs.
Auxiliary be
The auxiliary verb be is used:
1) in the formation of the continuous
tenses
I am writing.
She was singing.
It was raining.
They were playing.
2) in the formation of passive verb forms
I was shocked.
The boys were praised.
He was questioned.
Be can be followed by an infinitive. This
structure is used to talk about an arrangement, a plan, an agreement or a command.
I am to see him tomorrow. (Arrangement)
They are to be married next month.
You are to leave at once.
Auxiliary verb have
The auxiliary have has the following uses:
1) in the formation of the perfect tenses
She has come.
They have returned.
She has been waiting.
2) with the infinitive to indicate
obligation
I have to be there by 12 o’clock.
She has to finish the work.
Had + infinitive can be used to talk about an obligation
that existed in the past.
I had to be there by 12 o’clock.
Notes:
In questions and negatives, have
to and had to are used with do, does and did.
Compare:
She had to go.
Does she have
to go?
She doesn’t have
to go.
They have to go.
Do they have
to go?
They don’t have
to go.
I had to go.
Did I have
to go?
I didn’t have to go.
