Are there any difference in using 'must' and 'have to'? I heard many different version of this matter, but I don't know still how to use this words. Thank you. Kate
One thing about "must" is that it is often used for rules and regulations.
If a speaker uses "must" it often communicates something more serious.
They're sometimes interchangeable as well. It depends on the context.
I've heard students use "must" when "have to" would be more appropriate.
There's "have got to", which could sound more emphatic. "Have got to" is often more suited to informal types of speaking as in "I've got to get going now" or "I've got to return these DVDs to the video-rental store. "Have got to" is not reserved for informal speaking, however. Anyone could use it in most any type of circumstance.
Remember, also, that "have to" and "must" are not just used to express types of obligation, but also to give what we could call emphatic recommendations.
You must see that movie. You've got to read this article.
Then there's expressing disbelief.
You must be joking. You have to be joking.
You can use them to express certainty as well.
My glasses must be in this room somewhere. You must be Joe. This has to be the place.
Here you can observe how they are used by native speakers in different contexts. It's all about context, the speaker's viewpoint, and speaking style. There are guidelines to what is usual and typical. However, there aren't any hard and fast rules in this particular case.