Saying ‘Yes, I do. / No, I don’t’ in English is more polite than just saying ‘Yes. / No.’ That’s why short answers are very commonly used.
To form the short answer, you use the first word from the question. (This is either an auxiliary verb or a form of ‘be’.)
Use the long form (he does) in affirmative answers (yes).
Use the short form (he doesn’t) in negative answers (no).
|Do we know him?||Yes, we do.||No, we don’t.|
|Can she see me?||Yes, she can.||No, she can’t.|
|Have they read the book?||Yes, they have.||No, they haven’t.|
|Is he hungry?||Yes, he is.||No, he isn’t.|
Mind: If ‘you’ is the subject of the question, ‘you’ must be replaced by ‘I’ or ‘we’.
|Do you know him?||Yes, I / we do.||No, I / we don’t.|
If the question starts with ‘are you’, ‘are’ must sometimes be replaced by ‘am’.
|Are you hungry?||Yes, I am.||No, I’m not.|
|But: →||Yes, we are.||No, we aren’t.|