We use must and have to to say that it is necessary to do
something. Sometimes it doesn't matter which you use:
- Oh, it's later than I thought. I must go. or I have
to go.
But there is a difference between must and have
to and sometimes this
is important:
Must is personal. We use must when we give our personal feelings. 'You must do something' = 'I (the speaker) say it is necessary':
- She's a really nice person. You must meet her. (= I say this
is neccessary)
- I haven't phoned Ann for ages. I must phone her tonight.
Compare:
- I must get up early tomorrow. There are a lot of things I want
to do.
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Have to is impersonal. We use have to for facts, not
for our personal feelings.
'You have to do something' because of a rule or the situation:
- You can't turn right here. You have to
turn left. (because of
the traffic system)
- My eyesight isn't very good. I have to
wear glasses for reading.
- George can't come out with us this evening. He has
to work.
- I have to get up early tomorrow.I'm going away and my train
leaves at 7.30.
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If you are not sure which to use, it is usually safer to use have
to.
You can use must to talk about the present or future, but not the past:
- We must go now
- We must go tomorrow. ( but
not 'We must go yesterday')
You can use have to in all forms. For example:
- I had to go to hospital. (past)
- Have you ever had to go to hospital? (present
perfect)
- I might have to go to hospital. (infinitive after might)
In questions and negative sentences with have to, we normally use do
/ does / did:
- What do I have to do to get a driving licence ? (not 'What have I
to do?' )
- Why did you have to go to hospital ?
- Karen doesn't have to work on Saturdays.
Mustn't and don't have to are completely different:
You mustn't do something = it is necessary that you do not do
it (so, don't do it):
- You must keep it a secret. You mustn't
tell anyone. (= don't
tell anyone )
- I promised I would be on time. I mustn't
be late. (= I must
be on time )
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You don't have to do something = you don't need to
do it (but you can if you want):
- You can tell me if you want but you don't
have to tell me.
(= you don't need to tell me)
- I'm not working tomorrow, so I don't have
to get up early.
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You can use 'have got to' instead of 'have to'. So you can say:
- I've got to work tomorrow. or I have
to work tomorrow.
- When has Ann got to go ? or When does Ann have
to go ?
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