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Acting as auxiliaries

Modal + bare-infinitive

Never changing forms (no -s, -ed or -ing)

Used with progressive (be + v-ing) and perfect (have + p.p) aspects

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Can/Could => ability

May/Might => permission

Will/Would => prediction

Shall => prediction

Should/Ought => escapable obligation or duty

Must => inescapable obligation

Needn't => absence of obilgation

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Can/Could => natural or learned ability

E.g. Can you run 1500 meters in 5 mins?

Can you drive a car?

Jim could run very fast when he was a boy.

Barbara couldn't sing very well when she was younger.

Be (un)able to

Be (in)capable of

Manage to

Succeed in

Could/Was/Were able to => acquisition of a skill after effort

E.g. I tried again and found I could/was able to swim

Was/Were able to, managed to, succeeded in => specific achievement in the past (happening for only 1 time)

E.g. In the end they managed to rescue the cat on the roof. (...couldn't rescue the cat...)

Can/Could + verb of perception (NOT be able to)

Could ~ would be able to => “unreal past” (unreal/ unlikely situations NOT in the past)

Could have/ would have been able to => ability not used due to personal failure or lack of opportunity

E.g. I'm sure you could get into university (if you applied).

I could slap your face.

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(not) be allowed to

(not) be permitted to

Be forbidden to

Be not to

Very polite…

Can/could I (possibly)…

Do you think I could/might use your phone?

I wonder if I could/might…

Might I (possibly) be allowed to…?

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A certain fact

A possibility

She could/may/might be at home (Perhaps British accent/Maybe American accent she’s at home)

Past possibility

A certain fact

A possibility

Less common for possibility

Question about possibility

E.g. May/Might this be true?

Might/Could he know the answer?

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Certainty/ Facts

Deduction

E.g. He must live here./ He must be leaving.

He can’t live here/ He can’t be leaving.

He must have lived here./ He must have been leaving.

I’m sure that he lives/lived here

I’m sure it rained last night <- It must have rained last night.

I’m sure it didn’t rain last night <- It can’t/couldn’t have rained last night.

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Request with things/substances

Request with action

Will/Would you (kindly) open the door for me (please)? (about willingness)

Can/could you (possibly) open the door (please)?  (about ability)

Would you mind opening the window for me (please)?

Response

Yes, of course

No, I’m afraid I can’t

Not at all, no problem

Suggestions/Invitations with actions

Offers with action

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“Should”: it’s advisable to/ it’s (my) duty to

“Ought to” slightly stronger than should, regulations or duties imposed from the outside

“Had better”: the strongest (some specific future action) + threat/warning/urgency

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“Have to”: inescapable obligation coming from outside (a regulation, an order from somebody, etc)

“Have got to”: frequently used in writing ~ have to

“Must”:  inescapable obligation coming from the speaker (or the hearer in the questions)

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Advisability/ Necessity in the past

I should have been at the office before 9.

I ought to have left/ have been leaving London before 9.

Lack of necessity

Inadvisability

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He will always complain if he gets the opportunity

When we were students we would often stay up all night

Jackie used to make all her own dresses.

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I used to smoke, but I don’t anymore/any longer.

I never used to eat a large breakfast, but I do now.

I collected stamps when I was a child. = I used to collect stamps