Do is one of three auxiliary verbs in English: be, do, have. We use do to make negatives (do + not), to make question forms, and to make the verb more emphatic.
I didn’t see you at the concert the other night.
Do they open at nine o’clock on weekdays?
He does look smart in his new suit!
Question (?) form
To make the question form of most main verbs, we use do, does (present simple) and did (past simple) followed by the subject and the main verb:
Do you play football?
Doesn’t he phone you now and then?
Did your mother come from the same place as your father?
Negative (−) form
The negative of the present simple and past simple of all main verbs (except for be and some uses of have as main verbs) is made with auxiliary do + not, which is shortened to don’t (do not), doesn’t (does not) and didn’t (did not). We use the short forms in everyday informal language, and the full forms in more formal situations:
I don’t want to wait for a bus. Let’s get a taxi.
Jack doesn’t live in the town centre. He’s out in the suburbs.
Didn’t you get my email? I sent it at about four o’clock.
The Prime Minister does not take personal phone calls from members of the public. (more formal)
Did the parents not realise that something serious had happened to their child? (more formal)
We use do, does (present simple) or did (past simple) to give extra force to the main verb. We use the infinitive of the main verb without to, and stress do/does/did when speaking.
I like your new jacket.
I do like your new jacket!
She looks so tired.
She does look so tired!
I didn’t recognise your dad, but I recognised your mum.
I didn’t recognise your dad, but I did recognise your mum.
We also use emphatic do with imperatives.
Do come and have dinner with us some time.
Do stop talking, Harry! You’re boring everybody!
We use auxiliary do to form question tags for clauses which do not have a modal verb, a verb in the perfect with have or clauses with be. The tag uses the same person and tense as the subject of the main verb. The tag may be affirmative or negative, depending on the type of tag:
You work with Peter, don’t you? (affirmative main verb, negative tag)
She plays the piano, doesn’t she?
Little children don’t usually like spicy food, do they? (negative main verb, affirmative tag)
They didn’t stay very long, did they?
You live near Harkness, do you? (affirmative verb, affirmative tag)