Must vs. Have to

Must vs. have to
Both Must and have to express obligation or necessity, but there are some small differences:
- We use must when the speaker thinks it is necessary or important to do an action:

Must you go? ~ Yes, I must.
You must go. (= It is important that you go.)

- We use have to to talk about an action that is necessary because of rules or laws, or because someone obliges us to do it:

 Doctors sometimes have to work on Sunday.
(It is in the rules of their work.)