Auxiliary verbs Do and Can

Uses of do

The auxiliary do is used:

1) to form the negative and interrogative of the simple present and simple past tenses.

He came. (Affirmative)

He did not come. (Negative)

Did he come? (Interrogative)

He works. (Affirmative)

He does not work. (Negative)

Does he work? (Interrogative)

2) To avoid repetition of an ordinary verb, as in the following examples.

‘Do you know him?’ ‘Yes, I do.’ (= Yes, I know him.)

‘She sings well.’ ‘Yes, she does.’ (= Yes, she sings well.)

Do is also used to emphasize the affirmative nature of a statement.

She did come.

You do look upset.

Do can be used in the imperative mood to make a request or invitation sound more persuasive.

Do be quiet.

Uses of Can

Can usually expresses ability.

He can speak ten languages.

I can knit.

Can you lift this box?


Can is often used in the sense of may to give permission, though may is more correct.

You can go now.

You can take one of those books?

Now-a-days can is also being used to ask permission.

Can I come in, sir?


Can is often used in negative and interrogative sentences to talk about possibility.

Can this be true?

No, it can’t be.

In affirmative clauses we use may to express possibility.

It may rain.