Auxiliary Verb Do

Do has three main uses.

As an Auxiliary Verb

The auxiliary do is used to make emphatic, interrogative and negative verb forms. It is followed by an infinitive without to.

§  Did you post the letters?

§  Do you like football? 

§  This doesn't taste very nice 

§  Do sit down. 

§  I do admit that I was wrong. 

§  He did come.

Note that we use do to make questions and negatives with ordinary verbs, but not with other auxiliary verbs.

§  Do you like dancing? (NOT Like you dancing?)

§  I don't like reading. (NOT I like not reading.)

§  Are they sleeping? (NOT Do they are sleeping?) 

§  I will not come. (NOT I do not will come.) 

§  Will you help me? (NOT Do you will help me?) 

§  I can't see anything. (NOT I do not can see anything.) 

To make imperative sentences

Do can be used with be to make imperative sentences.

§  Don't be silly! 

§  Do be quite! 

§  Do be a good child. 

As an ordinary verb

Do is also an ordinary verb. The ordinary verb do can refer to almost any kind of activity.

§  What were you doing in the morning? 

§  What did you do then? 

§  Do as I tell you. 

§  It was a stupid thing to do. 

§  Can't you do it yourself? 

§  You are a grown up man now. You should be able to do things on your own. 

§  Do with me what you like. 

§  I don't know what I did to make her angry. 

The auxiliary do and ordinary do can sometimes occur together.

§  What did you do then? (Did - auxiliary, do- ordinary) 

§  I don't do well in mathematics. (Don't-auxiliary, do- ordinary) 

Note that the ordinary do has infinitives (to do, to be done) and participles (doing, done).

Do - Other uses

Do can be used to avoid repeating a verb or a verb phrase.

§  She looks much younger than her husband does. (= ...her husband looks.) 

§  May I join you? Please do. (= Please join us.) 

§  Who said that? I did. (= I said that.) 

§  I thought I would take a day off school today. No you don't. (= You are not going to take a day off.)