Модальные глаголы - must и have to

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What the difference between must and have to? Or it's simply synonyms?...

1) used as an auxiliary to express obligation or compulsion: YOU MUST PAY YOUR DUES. In this sense, must does not form a negative. 
2) used as an auxiliary to indicate necessity I MUST GO TO THE BANK TOMORROW.
In any case we can say: I MUST GO TO THE BANK. (because I work there. necessity)
and I HAVE TO GO TO THE BANK. (because I want to get some money. more wishful action than necessity)

Must is modal verb. Must ,like have to,express strong obligation.Must express an obligation that involes the speaker's opinion.It is personal.
Have to isn't a modal verb.Have to expresses strong obligation.
Have to and must are sometimes interchangeable.But have to is used more often then must.If you are unsure which to use,it is probably safer to use have to.
Don't have to and mustn't are completely different.
Don't have to expresses absence of obligation-you can but it isn't necessry.(you can choose)
Mustn't expresses negative obligation-it is very important not to do something.

I'm American. My wife is Russian. She was reading this site and I noticed this post and thought I would respond. The difference between "must" and "have to" is slight. When you say "Have to", it usually indicates something that you do not really want to do, or something that will have bad consequences if you do not do it. "Must" on the otherhand, generally refers to anything that you need to do, without the not wanting to or bad consequences implied. Also, "Must" is slightly more formal, and is not used as much today as it was years ago.

Have to and must, don`t have to and mustn`n
1. Have to and must are sometimes interchangeabl.
I must be home by midnight. I have to be home by midnight.
But have to used more often then must. If you are unsure which to use, it is probably safer to use have to.
2.Must I...? is possible, but question forms with have to are more common.
Do I have to do whot you say, or can I do whot I want?
3. Have to has all forms; must does not.
4. Don`t have to and mustn`t are completly different.
Don`t have to expresses absence of oblilgation- you can but it isn`t necessary.
When you go into a shop, you don`t have to buy something. You can just look.
Mustn`t expresses negative obligation- you can but it isn`t necessary.
You mustn`t steal other people`s things. It`s wrong.

Mustn`t expresses negative obligation- you can but it isn`t necessary.
You mustn`t steal other people`s things. It`s wrong. -
I think you are wrong. On the contrary MUST NOT means strict prohibition.

Must is personal. We use  must  when we give our personal feelings. eg i must do something(it`s necessary) Have to is impersonal. We use have to for facts. Must use in present and future.eg i must go tomorrow.

I will try to explain the difference between MUST and HAVE TO.
Actually, MUST and Have To have a very similar meaning. HAVE To is more common for GENERAL,EXTERNAL obligations, for example rules and laws.
MUST is more common for SPECIFIC or PERSONAL obligations.
For example
1. I have to wear a tie at work( it is a rule)
2.I must buy a new shirt(itis your own decision).
HaVE TO exists in all Tense
Must is a modal verb.there are two forms are must and mustn't.
By the way you can use HAVE to and Must for strong recommendations, for example- YOU have to/must see that film.
Hope I was be able to help you.
Have a nice day

Olga, if I'm not mistaken you've forgotten the main difference between these two modal verbs sinse rules,laws are examples of ONE common meaning or something like this. So, when you are going to epress the actions that do not depend on you(some kind of circamstances) you sould use 'have to'. As for must it supposed to be used in a great amount of meanings. Some of them have already been mentioned. also 'must' denotes a very strong possibility of some events. 
E.G. he must be hire at 5 o'clock( that is he will definitely be hire at 5 o'clock/ Talking about other mneanings there is very interesting one of prohibition. 
e. g. you must not touch this! (a very rude form of modal expression "you're not allowed to) I hope it ' will help someone. 
Best of luck to everybody.


  • Use have to + infinitive to talk about rules and obligations, or to say something is necessary.
  • Use don’t have to + infinitive to say there is no obligation, or something is not necessary.
  • Use must + infinitive to talk about rules and obligations.
  • Use mustn’t + infinitive to say something is prohibited.
  • You can use mustn’t or can’t to talk about rules.

! Must and have to are very similar, but there is a small difference. We normally use have to for a general obligation (a rule at work or a law). We normally use must when the speaker imposes the obligation (for example, a teacher to students or a parent to children). But often you can use eighter.

! Mustn’t and have to have completely different meanings. 
You mustn’t go = You can’t go. It’s prohibited.
You don’t have to go = You can go if you want, but it’s not obligatory/necessary.
(By Oxford University Press, Pre-Intermediate St's Book)



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