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 necessary)
* 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.
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.
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)
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.
You can use 'have got to' instead of 'have to'. So you can say:
* I've got to work tomorrow. or have to work tomorrow.
* When has Ann got to go? or When does Ann have to go?
EXERCISES
31.1 Complete these sentences with must or have to (in the correct form). Sometimes it is possible to use either; sometimes only have to is possible.
1. It's later than I thought. I must or have to go now.
2. Jack left before the end of the meeting. He had to go home early.
3. In Britain many children. --- wear uniform when they go to school.
4. When you come to London again, you --- come and see us.
5. Last night Don became ill suddenly. We --- call a doctor.
6. You really --- work harder if you want to pass the examination.
7. I'm afraid I can't come tomorrow. I.. --- work late.
8. I'm sorry I couldn't come yesterday. I --- work late.
9. Paul doesn't like his new job. Sometimes he --- work at weekends.
10. Caroline may --- go away next week.
11. We couldn't repair the car ourselves. We --- take it to a garage.
12. Julia wears glasses. She --- wear glasses since she was very young.
31.2 Make questions with have to.
1. I had to go to hospital last week. Why did you have to go to hospital?
2. I have to get up early tomorrow. Why --- early?
3. Ann has to go somewhere now. Where --- she ---.
4. George had to pay a parking fine yesterday. How much ---.
5. I had to wait a long time for the bus. How long ---.
6. I have to phone my sister now. Why ---
7. Paul has to leave soon. What time ---
31.3 Complete these sentences using don't/doesn't/didn't have to + one of these verbs:
do get up go go pay shave wait work
1. I'm not working tomorrow, so I _don't have to get up_ to early.
2. The car park is free-you --- to park your car there.
3. I went to the bank this morning. There was no queue, so I ---.
4. Sally is extremely rich. She ---.
5. We've got plenty of time. We --- yet.
6. Jack has got a beard, so he ---.
7., I'm not particularly busy. I've got a few things to do but I ---them now.
8. A man was slightly injured in the accident but he --- to hospital.
31.4 Complete these sentences with mustn't or don't/doesn't have to.
1. I don't want anyone to know. You _mustn't_ tell anyone.
2 He doesn't have to wear a suit to work but he usually does.
3. I can stay in bed tomorrow morning because I --- go to work.
4. Whatever you do, you --- touch that switch. It's very dangerous.
5. There's a lift in the building, so we --- climb the stairs.
6. You --- forget what I told you. It's very important.
7. Sue --- get up early. She gets up early because she wants to,
8. Don't make so much noise. We --- wake the baby.
9. I --- eat too much. I'm supposed to be on a diet.
10. You --- be a good player to enjoy a game of tennis.
31.1
3 have to
4 must or have to
5 had to
6 must or have to
7 have to
8 have to
9 has to
10 have to
11 had to
12 has had to
31.2
2 do you have to get up/have you got to get up
3 does (she) have to go?/has (she) got to go?
4 did he have to pay?
5 did you have to wait?
6 do you have to phone her now?/have you got to phone her now?
7 does he have to leave?/has he got to leave?
31.3
2 don't have to pay
3 didn't have to wait
4 doesn't have to work
5 don't have to go
6 doesn't have to shave
7 don't have to do
8 didn't have to go
31.4
3 don't have to
4 mustn't
5 don't have to
6 mustn't
7 doesn't have to
8 mustn't
9 mustn't
10 don't have to
