A》 Must has just one form and is followed by an infinitive without to.
● You must wear something smart.
Have to has both present and past forms.
● We have to wear something smart.
● David has to work on Sundays.
● I had to get up early today.
We form negatives and questions with do.
● We don’t have to wear smart clothes.
● What time did you have to get up?
Have to can be continuous or perfect and has an infinitive and ing-form.
● I’m having to do the work of two people.
● We’ve had to make a few changes.
● I don’t like to have to wait around.
● It’s no fun having to stand all the way.
Must and have to refer to what is necessary now or in the near future.
● I’m really sweaty. I must have a shower.
● We must make the arrangements soon.
● We have to turn left here. It’s one-way.
● Mark has to take an exam next week.
For the near future we can also use will have to.
● I have to go / I’ll have to go out soon.
We sometimes use must to recommend something enjoyable.
● You really must watch this programme.
There is a difference in meaning between must and have to.
We normally use must when the speaker/writer decides what is necessary, and we use have to when the necessity comes from the situation.
● You must wait in the queue. (I’m telling you.)
● You have to wait in the queue. (That’s the rule.)
● I must go on a diet. I want to lose weight.
● I have to go on a diet. Doctor’s orders.
Instead of have to, we can use have got to. The meaning is the same.
● I have to fill this form in.
● I’ve got to fill this form in.
● Does everyone have to register?
● Has everyone got to register?
Have got to is informal and used mostly in the present simple. In the past had to is more usual than had got to.
● I couldn’t go out because I had to finish my project.
We do not use got in the perfect or continuous, the infinitive, or the ing-form.