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 get up early tomorrow. My flight leaves at 7:30.
Jason can’t meet us tonight. He has to work late.
Last week Nicole broke her arm and had to go to the hospital.
Have you ever had to go to the hospital.
We use do / does / did in questions (for the present and past simple):
What do I have to do to get a driver’s license? (not What have I to do?)
Does Kimberly have to work tomorrow?
Why did you have to leave early?
In negative sentences, we use don’t / doesn’t / didn’t:
I don’t have to get up early tomorrow. (not I haven’t to)
Kimberly doesn’t have to work on Saturdays.
We didn’t have to pay to park the car.
You can say:
I’ll have to / I won’t have to …
I’m going to have to …
I might / may have to … (= perhaps I’ll have to)
They can’t fix my computer, so I’ll have to buy a new cone. or
… so I’m going to have to buy a new one.
I might have to leave the meeting early. or I may have to leave …
Must is similar to have to:
The economic situation is bad. The government must do something about it.
The government has to do …
If you go to New York, you really must visit the Empire State Building.
(or … you really have to visit …)
But have to is more common that must.
We use especially in written rules and instructions:
Answer all the questions. You must write your answers in ink.
Applications for the job must be received by May 18.
You must not do something = it is necessary that you not do it (so don’t do it):
Students must not use cell phones in class. (= it is not allowed)
Compare must not and don’t have to:
You must keep this a secret. You must not tell anybody.
(= don’t tell anybody)
You don’t have to tell Tim about what happened. I cal tell him myself.
(= you don’t need to tell him, but it’s OK if you do)
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.
He’s got to visit his aunt tonight. or He has to visit his aunt tonight.