Can anybody please explain me the main differences between "Must" and "Have to"?
I can't really understand their differences. I mean, I know that both are used in similar way. Someone told me that "Must" express more obligation than "Have to". Is that true? Does exist any rule or grammar use for each one? When do I use them? Thank you very much!!
Here's a pretty good description of the difference: http://www.englishgrammarsecrets.com/musthaveto/menu.php
When used to talk about obligation, there's only a subtle difference between the two words (in the affirmative).
- Use "must" or "will have to" when there's a strong internal obligation to do something.
- Use "have to" when there's a strong external obligation to do something.
In the negative, there's a big difference:
- "Must not" is a strong obligation NOT to do something.
- "Don't/doesn't have to" simply implies the lack of an obligation.
I wouldn't say that either expresses "more" obligation necessarily, but I would say that "must" is more formal. In normal speech, I generally stick to "have to" or "will have to".
Thank you very much, but I still don't get it in totally. What happen with public signs or advices? For example; (In library) You must be quiet.
In the context of commands on public signs, it's more common to avoid using either word. For example, "be quiet" or "please be quiet" in libraries.
If you do see "must" on a public sign, it's likely influenced by the other definition - "expressing certainly or an implied agreement among all parties". In your example of seeing "You must be quiet" in a library, the sign might also read "Everybody acknowledges that we should all be quiet" or "It is certain that we're all going to be quiet here."
This is in contrast to "have to", which implies agreement by only one side. I have to be quiet means "The librarian wants me to be quiet, so I will (but I don't want to!)".
Another example can be seen in hotels. You could imagine that a hotel sign reading "Guests must check out before 11am" has the implied meaning "According to the rules (which we all understand to be 100% true), guests check out before 11am."
I hope that helps you a little. Like I said, it's a subtle difference. You'll be mostly understood no matter which word you use :)
Must means that you have to do it even if you do not like it. Have means that you have to do it , but you can decide when or change your mind and not do it.