Obligation and advice: should and ought to, be supposed to
We use ought to and should to talk about obligations and duties in the future, present and past, or to give advice
– You ought to/should speak English in class.
– Shouldn’t we tell someone about the accident?
– Oughtn’t we to have invited Mandy?
We can use be supposed to when saying what someone should or should not do according to rules or regulations
– You‘re not supposed to park here.
Should + have + past participle is often used to criticise your own or other people’s behaviour
– I should have told you before.
– You shouldn’t have promised that.
Other phrases for advice
– It is advisable/wise to keep documents in a safe place.
– You should remember that…
– Travellers are reminded that banks close on Saturdays.
– Guests are recommended to keep documents in a safe place.
Lack of obligation or necessity
We use needn’t, don’t need to, don’t have to to talk about a lack of obligation, in the present or future
– You don’t need to/needn’t meet me at the station.
– We don’t have to wait. We can go straight in.
We use needn’t + have + past participle to say that somebody did something, but that it was unnecessary
– You needn’t have gone to all that trouble.
We use didn’t need to + infinitive to say that something wasn’t necessary without saying whether the person did it or not
– You didn’t need to bring any extra money.
Asking for and giving permission
We can use to ask for and give permission
– Can I borrow your calculator for a few minutes.
– Yes, you can stay up and watch the late night film.
– You can’t wait here. It’s private. (= not allowed to)
We use could to ask for permission when we are not sure what the answer will be
– Could I open the window? Yes, of coure you can.
Watch Out! could is not used for giving permission.
We use may to ask for or give permission in formal situations
– May I take that chair?
– You may use pen or pencil.