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?
Permission
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?
Possibility
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.
