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