English Grammar in Use – Unit 31: “Have to” and “Must”

Part A:

I have to do something= it is necessary to do it, I am obliged to do it:
You can’t turn right here. You have to turn left.
I have to wear glasses for reading.
Robert can’t come out with us this evening. He has to work late.
Last week Tina broke her arm and had to go to hospital.
I haven’t had to go to the doctor for ages.
You have to turn left here.
We use do/does/did in questions and negative sentences (for the present and past simple):
What do I have to do to get a new driving licence? (not What have I to do?)
Karen doesn’t have to work Saturdays. (not Karen hasn’t to)
Why did you have to Leave early?
You can say I’ll have to … , I’m going to have to … and I might / I may have to … :
They can’t fix my computer, so I’ll have to buy a new one. or
I’m going to have to buy a new one.
Tom might have to work late tomorrow. or Tom may have to work … (=it’s possible that he will have to)

Part B:

Must is similar to have to:
It’s later than I thought. I must go. or I have to go.
You can use must or have to to give your own opinion (for example, to say what you think is necessary, or to recommend someone to do something):
I haven’t spoken to Sue for ages. I must phone her. or I have to phone her. (= I say this is necessary)
Mark is a really nice person. You must meet him. or You have to meet him. (I recommend this)
We use have to (not usually must) to say what someone is obliged to do. The speaker is not giving his/her own opinion:
I have to work from 8.30 to 5.30 every day. (a fact, not an opinion)
Jane has to travel a lot for her work.
But must is used in written rules and instructions:
Applications for the job must be received by 18 May.
(exam instruction) Answer all the questions. You must write your answers in ink.
You cannot use must to talk about the past:
We didn’t have much time. We had to hurry. (not we must hurry)

Part C:

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 this a secret. You mustn’t tell anyone. (= don’t t ell 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 don’t have to tell Tom what happened. I can tell him myself.
I don’t have to be at the meeting, but I think I’ll go anyway.
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 Helen got to go? or When does Helen have to go?

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