Tra từ must - Từ điển Oxford Learners Wordfinder Dictionary

1 ways of expressing what must be done
2 things that must be done
3 making sb do sth
things that you need to have NEED
see also POSSIBLE

1 ways of expressing what must be done
※ necessary to do sth
- if you think that it is necessary that sb does sth, you can say that they must (do sth), have to (do sth), have got to (do sth), need to (do sth)
You must try to be on time in future! ◎ Must she go away? ◎ Do I have to show my passport? ◎ Sorry, I've got to go. ◎ Have we got to listen to another speech? ◎ I need to get up at half past six if I'm going to catch the 8.15 train.
- to say that sth was necessary in the past, you can say that sb had to (do sth), needed to (do sth)
I'm sorry I'm late. I had to go to the bank. ◎ 'Why did you come back?' 'I needed to see you.'
Note: must often suggests that sth is necessary because the speaker wants it to be done; have to often suggests that sth is necessary because of the situation or because of a law or a rule; have got to is a little more informal than have to; need to often suggests that sth is necessary if sth else is to be possible.
※ necessary not to do sth
- if you think that it is necessary that sb does not do sth, you can say that they must not (do sth)
You must not say that! They won't like it at all! ◎ I mustn't forget to put the chicken in the oven before we go out.
- if you want to say that it is necessary not to do sth because it is not permitted, you can say that sb is not allowed to (do sth) or can't (do sth)
We weren't allowed to smoke at my school. ◎ We can't wear jeans in my office.
※ more on being allowed to do sth ALLOW
※ not necessary to do sth
- if you think that it is not necessary that sb does sth, you can say that they don't have to (do sth), haven't got to (do sth), don't need to (do sth), needn't (do sth)
You don't have to wear a tie, but you can if you want. ◎ I'm so glad I haven't got to go into hospital. ◎ George doesn't need to go to the dentist again, does he? ◎ 'Have I really got to do my homework now?' 'No, you needn't do it now, but you'll have to after supper.'
- to say that sth was not necessary in the past, you can say that sb didn't have to (do sth), didn't need to (do sth), needn't have (done sth)
Are you telling me now that I didn't have to re-type those letters? ◎ It was kind of you to help, but you really didn't need to, you know. ◎ I now realize that I needn't have done all that cleaning.
※ right or desirable (but not necessary)
- if you think that it is right or a good idea that sb does sth, you can say that they should (do sth), ought to (do sth)
Shouldn't I show you my essay again before I hand it in? ◎ You should try the chicken chasseur - it's extremely good. ◎ There ought to be more lights along this road - it's dangerous. ◎ Oughtn't you to go to the doctor with that cough?
- to give advice, you can also say that sb must (do sth)
You must try and see that film - it's brilliant.
- to say that sth was right or a good idea in the past, you can say that sb should have (done sth), ought to have (done sth)
You should have thought about that before you sold the house! ◎ We ought to have foreseen this.

2 things that must be done
- something that has to be done, because sb has said that you must do it or because you have promised to do it: obligation (noun C/U)
to have family obligations ◎ You're under no obligation to buy.
- if you officially have to do sth, it is compulsory, obligatory
It's obligatory to carry some form of identification with you.
- not obligatory: optional
an optional course
- something that you have to do because the situation requires it: necessity; adjective: necessary
Wearing a cycle helmet is a real necessity in town. ◎ Don't spend all the money unless it's absolutely necessary.
- absolutely necessary: essential, vital
A good diet is essential to a healthy life. ◎ It's vital that everyone is here on time.
- something that has to be done, either because it is your job or because you are morally obliged to do it: duty
I feel I have a duty to help him.
- to tell sb that they are free from a duty, responsibility, etc: excuse sb (from sth)
I was excused from games because of my bad leg.
- free from having to do sth or pay sth: exempt (from sth) (not before a noun); noun (C/U): exemption
exempt from military service
- to make sb exempt from sth: exempt sb (from sth)
※ more on duty DUTY

3 making sb do sth
- to make sb do sth: force sb to do sth, compel sb to do sth (usually passive), oblige (AmE obligate) sb to do sth (usually passive)
I felt compelled to tell them what I thought of the plan.
- to say to sb that they must do sth: tell* sb to do sth, order sb to do sth; noun: order
The policeman told the driver to get out of the car. ◎ to give sb an order
- to ask for sth in a way that shows that you expect to get it: demand sth/to do sth
I went into the shop and demanded to see the manager.
- to say that you must have sth, or that sth must happen: insist (on sth), insist that ※¦; noun (U): insistence
We insist on punctuality. ◎ I insisted that she tell me the truth.
※ more on giving orders ORDER