'Must' & 'Have to'

Found this on a post in a forum.

"Have to" and "must" have the same meaning in the affirmative and interrogative forms when referring to obligation. Some grammarians think that "must" is slightly stronger, but for all practical purposes, they mean the same thing:
Doctors have to attend medical school for several years before they can practice medicine.
Doctors must attend medical school for several years before they can practice medicine.

While "have to" and "must" can be used interchangeably, there are differences in usage, as Michael Swan observes in Practical English Usage (Oxford University Press, 1995).

Both verbs can be used in British English to talk about obligation. (In American English, 'have to' is the normal form.)
British English often makes a distinction as follows:
'Must' is used mostly to talk about the feelings and wishes of the speaker and hearer — for example, to give or ask for orders.
'Have (got) to' is used mostly to talk about obligations that come from "outside" — for example from laws, regulations, agreements and other people's orders.

Compare: I must stop smoking. (I want to.)
I have to stop smoking. Doctor's orders.

This is a terrible party. We really must go home.
This is a lovely party, but we've got to go home because of the baby-sitter.

Must you wear dirty old jeans all the time? (Is it personally important for you?)
Do you have to wear a tie at work? (Is there a regulation?).

Hope these explanations will help you understand the two terms better.

Cheers,
Ms Yu