Modal verbs

Modal verbs (use)	Use	Examples
CAN / COULD/ BE ABLE TO	Ability	I couldn't play any instruments last year, now I can play short songs; soon I'll be able to play longer songs. We haven't been able to go on holiday-
Can (ability in the present)
Could (ability in the past and conditional)
Will be able to (ability in the future) Have been able to ( perfect tenses)
CAN / MAY/ BE ALLOWED TO	permission	Ok, you can wear that today, but you won't be allowed to play in the concert without the uniform. I wasn't allowed to play last year. May I have another drink? You may leave when you have completed the exam.
Can (permission in the present)
May (permission in the present; slightly more formal
Was/were allowed to Will be allowed to ( permission in other tenses, future or past)
Must / have to / need to Needn't / don't have to	obligation	You must log in, but you don't have to create a new password each time. You don't have to wear a uniform. You needn't get there before 11. We need to work harder to pass our exams.
Mustn't	prohibition	You mustn't use mobile phones in class. You mustn't eat too many sweets.
+ must could might may _can't	Certainty and possibility	The answer might be A,B or C. It can't be C; so it must be A. It must be late, it's getting dark. That can't be true.
Should / ought to	advice	You should go to the dentist. You ought to attend lessons.