Why is "do" sometimes put before a verb? [duplicate]
Possible Duplicate:
Use of “do” in affirmative statements
Why do people sometimes use the words "do" or "does" in affirmative sentences?
For example:
A: We know a guy!
B: We do know a guy!
Why doesn't B just say: "Yes, we know a guy"?
And in general, why the use of "do" in affirmative sentences?
Do in affirmative sentences is used to put an emphasis on the positive fact.
Person A: I've heard you don't have the piano anymore.
Person B: Oh, that's not true! I do have the piano!