Can anyone help me think of a good and concise way to explain the difference between "yes" and "sure"?

Who are you explaining it to? If they are high level students you might need to go beyond this first simple explanation.

I think as a general statement, 'sure' can be used instead of 'yes' as a reply to questions asking for confirmation of a request. The person asking the question is probably expecting a 'yes' answer.

'Can you be there by 4:00?'
'Sure.' (confirmation of a request)

'Is it possible to have that delivered by Sunday afternoon?'
'Sure.' (confirmation of a request)

'Could you make sure Ken plays in the next game?'
'Sure.' (confirmation of a request)

>>> examples of where 'sure' doesn't work <<<

'Is the game on Thursday?'
'Yes.'

'Is Ken going to play in the next game?'
'Yes.'

** no action is being requested of the listener. We're just confirming facts **

There's also this usage, in response to an 'is it possible' question:

'That can't be right, can it?'
'Sure, it can.'

'Ken isn't going to play in the next game, is he?
'Sure, why not. He's had a few bad games, but he'll turn it around.'


That's off the top of my head. That may not be right. If someone else can add to that or point out where that's wrong, we'd all appreciate it.

In addition to the explanation above, it may help to add that "sure" is usually used in casual interactions, and has a flippant tone to it.