Permission, obligation and necessity.
Permission, obligation, and necessity
can/could, must, should, ought to, had better
1 Can I use your phone, as my battery seems to have died?
I couldn't take any photos in the gallery, so I bought some postcards.
If you want to apply for this job, you must be able to speak Spanish.
We should/ought to drive-it’ll be much quicker.
The most common modal verbs for talking about permission and obligation are can/could, must, and should/ought to.
We can also use May 17 to ask for permission, ag. May l use your phone?
Should you can take it as an advice
2 We should have/ ought to have driven it would have been quicker.
We can use should have or ought to have past participle to talk about past events which did not happen and which we regret.
3 You’d better post the parcels today or they won’t get there in time.
had better is stronger and more urgent than should/ ought to and is often used to give strong advice or a warning. It normally refers to the immediate future
The negative is had better not NOT hadn’t-better
mustn’t/don’t have to
You mustn't take photos during the performance
You don't have to tip here unless you think the service was especially good
mustn’t and don’t have to are completely different. - mustn't is used to express an obligation not to do something. - don't/doesn't have to is used to express an absence of obligation.
need
1 You usually need to check in at least two hours before a flight leaves.
You don't need to take a jacket. It’s going to be hot today.
We use need/don't need to + infinitive to say that something is necessary/unnecessary. You can use these forms for habitual, general, and specific necessity.
- We
needn'tlock the car, Nobody will steal it in this village. When we want to say that something is unnecessary on a specific occasion, we can also useneedn't + infinitive without to.
3 We needn't have booked/didn't need to book. The restaurant is empty!
When something was not necessary, but you did it, you can use wither needn't have past participle or didn't need to infinitive.
4 We knew the way, so we didn't need to use the satnav.
When something was not necessary, so you did not do it, you must use didn’t need to. Compare:
We didn’t need to book. It wasn’t necessary. We may have booked or we may not.)
We needn’t have booked. ( We booked, but it wasn’t necessary.)
be able to, be allowed to, be permitted to, be supposed / meant to
1 From tomorrow we won't be able to park in this street.
You’re not allowed/permitted to smoke in any public buildings in our country.
We often use person be able to or be allowed + to infinitive instead of can to talk about what is possible or permitted.
2 it is not permitted to take phones into the exam room.
it be permitted to + infinitive is used in formal situations, eg. notices and announcements, to say what can/can’t be done according to the law or to rules and regulations.
We don’t use it isn’t allowed to NOT allowed to take phones into the them room
3 We are supposed/meant to check out by 12.00. What’s the time now?
You aren't supposed/meant to park here-it’s reserved for teachers.
We can also use be supposed to/be meant to + infinitive to say what people should or shoulde’t do, often because of rules. There is often a suggestion that the rules are not necessarily obeyed, e.g. Students are not supposed/meant to have guests after 12:00, but everyone does