They WEREN'T ABLE TO finish the application in time.
She SHOULDN'T take that job because she'll be bored.
You HAVE TO find more up-to-date information for the report.
We AREN'T ABLE to get into the lecture hall yet.
He COULD ski really well before the accident.
You MUSTN'T go past the fence over there.
Lee MAY arrive later, but he's in a traffic jam at the moment.
You DON'T HAVE TO attend the debate if you don't want to.
COULD you help me with my CV later, please?
You CAN find the details at this website.
inability (past)
prohibition
ability (past)
lack of obligation / necessity
advice / suggestion
inability (present, future)
possibility
obligation
permission / request
ability (present, future)