Cytat: chippy
Must= rules
Have to = choice
The speaker who uses “must” articulates the obligation or necessity that comes from him. When the speaker relates someone else’s orders or regulations, he uses “have to.” The difference is subtle, but it is there:
You must work harder on your English (because I’m telling you to). You have to work harder on your English (to pass the test.)
She says she must work harder on her English (because she wants to). She says she has to work harder on her English (to pass the test)
I must dress formally for work (because that’s my style and I want to dress formally for work).
I have to dress formally for work (because my employer says so).
You must dress formally for work (because I think it is necessary for your professional persona, or because I am your boss).