vocabulary - What does "sure" mean?

How is sure different from yes? How is it different from other responses? When should I use it?

Answer

Sure is used to signal consent, or to put it another way, willingness to go along with something. It's often used in response to requests for permission:

Alice: Would you mind if I take the car?
Bob: Sure, go ahead.

In the above, Bob is willing to go along with the proposition of letting Alice use his car. Bob is not signalling literal agreement with Alice's words, which is exactly what yes does:

Alice: Would you mind if I take the car?
Bob: Yes, I would mind very much. Take the bus.

Compare the following:

Alice: Would you mind if I take the car?
Bob: No, go right ahead.

In this case, literal disagreement has the same illocutionary force as sure, so we can see that yes and sure don't mean the same thing. However, the opposite might be true in another situation:

Alice: Would you like some cake?
Bob: Yes, I'd love some.

Alice: Would you like some cake?
Bob: Sure, thank you.

Here, Bob's willingness to go along with Alice's proposition has the same force as literal agreement. No would signal the opposite:

Alice: Would you like some cake?
Bob: No, thank you.

In other words, sure signals consent, while yes and no signal literal agreement or disagreement.