Modals (Tablo)

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

He may be at the library

He may have been at the library

might

1. less than 50% certainty

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

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

You could have talked to your teacher.

4. less than 50% certainty

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)