can

ability

e.g. Can you play the piano? asking for and giving permission

e.g. "Mom, can I go the cinema tonight?"

"No, you can't. You have homework to do" offer

e.g. Can I help you? request, instruction

e.g. Can you switch on the light for me? capability

e.g. The summers in England can be really unpredictable. with be to make criticisms

e.g. Susan can be a real pain in the neck at times. can't

ability

e.g. I can't come to the game on Friday. when you feel sure something is not possible (opposite of must)

e.g. The tennis match can't be over yet. (I'm sure it isn't). could

possibility or uncertainty (can also use might)

e.g. He could be the one for you! request (more polite than can)

e.g. Could you switch on the light for me? suggestion

e.g. We could go on a picnic this afternoon.