The three verbs, BE, HAVE and DO, play an important role in English. They are called primary verbs. In fact, each of them may be used as an auxiliary verb or main verb. In the former case they are referred to as primary auxiliaries, as opposed to modal auxiliaries.
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Main Verbs
Let’s have a look at the three verbs being used as main verbs first:
BE as Main Verb
BE is used as a copular verb:
Sarah is a teacher.
His parents were on vacation.
You are sad.
This verb is used in questions and negative sentences without the auxiliary DO:
Is Sarah a teacher?
Sarah isn’t a teacher.
Were his parents on vacation?
His parents weren’t on vacation.
Are you sad?
You are not sad.
HAVE as Main Verb
HAVE is used as transitive verb:
I had a little dog.
She has a big head.
In questions and negative sentences the use of the auxiliary DO varies, but very often it can be used just like with any other lexical verb:
Did I have a little dog?
I didn’t have a little dog.
Does she have a big head?
She doesn’t have a big head.
DO as Main Verb
DO is usually used as transitive verb:
I always do my homework.
He did something special.
But it may be also used as an intransitive verb:
He did as I said.
She does well in math.
In questions and negative sentences we regularly use the auxiliary DO, just like with other lexical verbs:
Do I always do my homework?
I don’t always do my homework.
Did he do anything special?
He didn’t do anything special.
Did he do as I said?
He didn’t do as I said.
Does she do well in math?
She doesn’t do well in math.
Primary Auxiliaries
The three primary verbs are also used as auxiliary verbs. Just like any other auxiliaries, they are not used with the auxiliary DO in questions and negative sentences. Let’s have a look at them one by one:
BE as Auxiliary Verb
The auxiliary BE is used to mark the progressive aspect:
She is waiting for her husband.
They were dancing on the lawn.
The corresponding interrogative and negative forms would be:
Is she waiting for her husband?
Were they dancing on the lawn?
She isn’t waiting for her husband.
They weren’t dancing on the lawn.
It’s also used to mark the passive voice:
The car was stolen yesterday.
They are eaten regularly.
The corresponding interrogative and negative forms would be:
Was the car stolen yesterday?
Are they eaten regularly?
The car wasn’t stolen yesterday.
They aren’t eaten regularly.
HAVE as Auxiliary Verb
The auxiliary HAVE is used to mark the perfective aspect:
She has broken her leg.
The train had arrived.
The corresponding interrogative and negative forms would be:
Has she broken her leg?
Had the train arrived?
She hasn’t broken her leg.
The train hadn’t arrived.
DO as Auxiliary Verb
The auxiliary DO is used as an operator in interrogative and negative clauses if there is no other auxiliary. So, for example there is no auxiliary verb in the following sentences:
He knew the truth.
They live in Chicago.
He drives too fast.
In questions and negative sentences, the auxiliary DO must be used:
Did he know the truth?
Do they live in Chicago?
Does he drive too fast?
He didn’t know the truth.
They don’t live in Chicago.
He doesn’t drive too fast.
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