Must and have to are both used to talk about
obligations:
For example:
We must talk to her before
she leaves: you think this is very important, and you need to do it. The
obligation comes from you and your feelings.
I have to go into work early
tomorrow: you have no choice. The obligation comes from the situation, not from
you.
Native English speakers use have
to much more in conversation. It’s rare to use must to talk about
obligations in spoken English, but you can use must to talk about
obligations in your written English if you’re writing something more formal.
What about mustn’t and don’t
have to?
Must not means that something is forbidden.
You are not allowed to do this.
Don’t have to means that something is not
necessary. You can choose to do something or not.
In a non-smoking area you mustn’t
smoke, but in a smoking area you don’t have to smoke but you can if you
want to.
You use should to give advice or
express your opinion. For example:
You should go to bed earlier.
Then you wouldn’t feel so tired all the time. –> This is my advice. I think
it’s better for you to do this, but it isn’t necessary. It’s not an obligation,
so you still have a choice.
Another example giving advice:
You should try the fish.
Using must or have
to expresses stronger feelings than just using should: it is stronger
and more emphatic.
You must try the fish!
You have to try the fish!
However, if you want to give
negative advice, only shouldn’t is possible.
You shouldn’t eat so much chocolate at once—you’ll make yourself sick!
