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.