Como usar Must and Have to

Must and have to is used to say that it is necessary to do something. Sometimes is does not make difference which you use:

• It is becoming later. I have to go. or I must go.

But there is a difference between have to and must 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 is a really nice person. You must meet her.(=I say this is necessary)
• I have not called Mary for ages. I must call her tonight.

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 situation;

• You cannot turn left here. You have to turn right (because of the traffic system)
• Mike can't go to the movie with us tonight. He has to work.

Now, compare:

• I must get up early tomorrow. There are a lot of things I want to do.
• I have to get up early tomorrow. I am going away and my train leaves at 8:00.

Note: If you are not sure which one to use, it is safer to use have to.

You can use must to talk about present or future, but not the past:

• We must go now.
• We must tomorrow.

You can use have to in all forms:

• I had to go to school.(past)
• Have you had to go to school.(present perfect)

In questions and negative sentences with have to, we use: do, does, did.

See you folks.