Modals Chart

Auxiliary	Uses	Present / future	Past
may	1. polite request	May I borrow your pen?
	2. formal permission	You may leave the room.
	3. Less than 50% certainty	--Where's Jon? He may be at the library	He may have been at the library
might	1. less than 50% certainty	--where's John? He might be at the library	He Might have been at the library
	2. polite request (rare)	Might I borrow your pen?
should	1. advisability	I should study tonight	I should have studied last night.
	2. 90% certainty	She should do well on the test (future only, not present)	She should have done well on the test.
ought to	1. advisability	I ought to study tonight	I ought to have studied last night
	2. 90% certainty	She ought to do well on the test. (future only, not present)	She ought to have studied last night.
had better	1. advisability with threat of bad result	You had better be on time, or we will leave without you.	(past form uncomon)
be supposed to	1. expectation	Class is supposed to begin at 10.	Class was supposed to begin at 10.
be to	1. strong expectation	You are to be here at 9:00.	You were to be here at 9:00
must	1. strong necessity	I must go to class today	I had to go to class yesterday
	2. prohibition (negative)	You must not open that door.
	3. 95% certainty	Mary isn't in class. She must be sick (present only)	Mary must have been sick yesterday.
have to	1. necessity	I have to go to class today.	I had to go to class yesterday
	2. lack of necessity (negative)	I don't have to go to class today.	I had to go to class yesterday.
have got to	1. necessity	I have got to go to class today.	I had to go to class yesterday.
will	1. 100% certainty	He will be here at 6:00 ((future only)
	2. willingness	--the phone's ringing. I'll get it.
	3. polite request	Will you please pass the salt?
be going to	1. 100% certainty	He is going to be here at 6:00 (future only)
	2. definite plan	I'm going to paint my bedroom. (future only)	I was going to paint my room, but I didn't have time.
can	1. ability / possibility	I can run fast.	I could run fast when I was a child but now I can't.
	2. informal permission	You can use my car tomorrow.
	3. informal polite request	Can I borrow your pen?
	4. impossibility (negative only)	That can't be true!	That can't have been true!
could	1. past ability		I could run fast when I was a child.
	2. polite request	Could I borrow your pen? Could you help me/
	3. suggestion	--I need help in math. You could talk to your teacher.	You could have talked to your teacher.
	4. less than 50% certainty	--Where's John? He could be at home.	He could have been at home.
	5. impossibility (negative only).	That couldn't be true!	That couldn't have been true!
be able to	1. ability	I am able to help you. I will be able to help you.	I was able to help him.
would	1. polite request	Would you please ass salt? Would you mind if I left early?
	2. preference	I would rather go to the park than stay home.	I would rather have gone to the park.
	3. repeated action in the past		When I was a child, I would visit my grandparents ever weekend
used to	1. repeated action in the past		When I was a child, I would visit my grandparents every weekend.
shall	1. polite question to make a suggestions	Shall I open the window?
	2. future with "I" or "we" as subject	I shall arrive at nine. (will = more common)