can

can’t

could

don’t have to

don’t need to

had better

have (got) to

may

may as well/might as well

ought to

shall

shan’t

should

will

would

(be) able to

ability, less used than can

e.g. I’m not able to come to the game on Friday.

can

ability

e.g. Can you play the piano?

asking for and giving permission

 e.g. “Mom, can I go the cinema tonight?”

“No, you can’t.  You have homework to do”

offer

e.g.  Can I help you?

request, instruction

e.g.  Can you switch on the light for me?

capability

e.g. The summers in England can be really unpredictable.

with be to make criticisms

e.g. Susan can be a real pain in the neck at times.

can’t

e.g. I can’t come to the game on Friday.

when you feel sure something is not possible (opposite of must)

e.g.  The tennis match can’t be over yet.  (I’m sure it isn’t).

possibility or uncertainty (can also use might)

e.g. He could be the one for you!

request (more polite than can)

e.g. Could you switch on the light for me?

suggestion

  e.g. We could go on a picnic this afternoon.

asking for and giving permission

  e.g. “Could I use your phone?”

“Yes, of course you can”

unwillingness

  e.g. I couldn’t possibly leave Tom alone while he’s in this state.

with comparative adjectives to express possibility or impossibility 

e.g. I could be fitter.

e.g. He couldn’t study harder.

don’t have to

when you don’t need to do something (but you can if you want)

  e.g. You don’t have to go to school if you don’t want to.

don’t need to

not necessary to do something (more used than needn’t)

 e.g. You don’t need to come to the party if you don’t want to.

had better

strong advice (less used than should)

  e.g. You’d better do the washing up now.

e.g. I’d better not go out tonight, because I have to get up early tomorrow.

have (got) to

necessity, impersonal, not for personal feelings, but for a rule or situation.  If you are unsure whether to use must or have to, it is usually safer to use have to.

e.g. I have to get up early tomorrow to catch the train to the office.

may

to express although in clauses

  e.g. I may be married to you, but that doesn’t give you the right to treat me like dirt.

possibility or uncertainty (formal)

  e.g. There may be a cure for AIDS within the next ten years.

asking for and giving permission (less usual, more formal) 

e.g. “May I use your phone?”

“Yes, of course you may”

may as well/might as well

describes the only thing left to do, something which the speaker is not enthusiastic about

  e.g. I’m so bored, I may as well do some housework.

might

possibility or uncertainty

  e.g. There might be a cure for AIDS within the next ten years.

unreal situation

e.g. If I knew her better, I might invite her to the ball.

must

when you feel sure something is true (opposite of can’t)

e.g. The tennis match must be over by now. (I’m sure it is).

necessity, personal feelings

  e.g. I haven’t spoken to Liz for ages.  I must give her a call.

order, strong suggestion

  e.g. You must stop smoking or you’ll get lung cancer.

must not

prohibition (negative order)

  e.g. You must not leave the table until you have finished your dinner.

need

as a normal verb

  e.g. Do you need me to help you?

in questions (less usual) 

e.g. Need you make so much mess?

needn’t

not necessary to do something (unusual)

  e.g. You needn’t come to the party if you don’t want to.

ought to

expectation (can use should)

  e.g. If you like Picasso, you ought to enjoy the exhibition.

recommendation (can use should)

e.g. You ought to have more driving lessons before you take the test.

criticism (can use should)

  e.g. You ought not to shout at your mother like that.

certainty or desire (mainly British English)

  e.g. I shall give up chocolate for Lent.

in formal rules and regulations (mainly British English)

  e.g. Racism or sexism shall not be tolerated in this building.

in questions to ask for instructions and decisions, and to make offers and suggestions (mainly British English)

  e.g.  What shall I do?

When shall we come and see you?

Shall we go to the cinema this evening?

shan’t

certainty (less usual, mostly British English)

e.g. I shan’t be late for the meeting.

expectation (can use ought to)

  e.g. If you like Picasso, you should enjoy the exhibition.

suggestion, advice, opinion (can use ought to)

  e.g. You should have more driving lessons before you take the test.

when something is not right or as you expect it

e.g. The price on this can of beans is wrong.  It should say $1.20, not $2.20.

criticism  (can use ought to)

  e.g. You shouldn’t shout at your mother like that.

uncertainty

  e.g. Should I ask her out on a date?

should + words of thinking, to make an opinion less direct

  e.g. I should think he could find a more compatible match.

with be and adjectives describing chance, including odd, strange, typical, natural, interesting, surprised, surprising, funny (=odd) and What a coincidence.

e.g. It’s odd that he should ask you so many personal questions.

after in case to emphasise unlikelihood

  e.g. I’m not going out tonight in case she should call me.

If…..should

e.g. If Jane should drop by when I am out, tell her to come back later.

polite order or instruction

  e.g. Applications should be sent by 3^rd January.

will

assumption

  e.g. Oh, that’ll be John on the phone.

request (can and could are more common)

e.g.  Will you go to the shop for me?

intention or willingness

  e.g. “I’ll take gran’s pearls then”.

“You won’t!”

“I will!”

order

  e.g.  Will you please shut up?

insistence

  e.g. “I won’t clean my room!”

“Yes you will!”

habits and typical behaviour

  e.g. Sarah will sit and gaze at the stars all night.

criticism

  e.g.  She will drink too much when she goes out.

won’t

emphatically forbid an action, in response to a will expression

  e.g. “I’ll take gran’s pearls then”.

“You won’t!”

“I will!”

refusal

  e.g. “I won’t clean my room!”

“Yes you will!”

request (can and could are more common)

  e.g.  Would you go to the shop for me?

would like - offer/invitation

  e.g.  Would you like a cup of tea?

after be, followed by adjectives doubtful, unlikely, to emphasise a tentative action

  e.g. It’s doubtful that he would be there in time of need.

annoying habit, typical of a person

  e.g. She would ask me for money, wouldn’t she?

certainty in a suppressed conditional sentence

  e.g. I would never agree to that. (even if he asked me)

certainty in a suppressed conditional sentence

  e.g. I wouldn’t agree to that. (even if he asked me.)