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Here we will study the verbs “Must” and “Have to” and get to know their differences. Both Have to and Must are used to express an obligation. Must is subjective and means that the speaker is the one who thinks this is an obligation. “Have to” is objective and means the speaker is the one being obliged.

• I must stop smoking.
• My parents warned me that I have to stop smoking.
• The teacher is strict so you must do your homework.
• The teacher is strict so you have to do your homework.
• You must visit London as it’s a beautiful city.
• You have to visit London as it’s a beautiful city.

As you see, ‘have to’ expresses an obligation due to outside effect, and ‘must’ is just an opinion of the speaker. In the case of the “You must visit London as it’s a beautiful city” sentence, the opinion is of the person saying it to you.

 

Also it is common in British English to say “have got to” instead of “have to”.

• I have got to get ready vs. I have to get ready.
• I have got to work vs. I have to work.
• He has got to be joking vs. He has to be joking.

“Will have to”, strangely, can mean the exact same as “must”:

• We will have to talk soon.
• They will have to arrive soon.
• She will have to call me.

 

“Must” is sometimes used to express a deduction and to certify that something is true. For example:

• You ate the cake alone so it must be delicious.
• Everybody is talking about Messi so he must be a good player.
• You look tired so you must have had a difficult day.
• He is happy so something good must have happened to him.
• This car is expensive so it must be good.
• This house is big so it must be nice.

In the negative forms the verbs have different meanings:

“Must not” means prohibition from doing something and is a strong obligation not to do it. “Must not” can be abbreviated as “mustn’t”.

• You must not break the law.
• The doctor told me that I must not drink alcohol.
• My mother told me that I must not go there.
• He must not go outside since he is sick.
• I mustn’t sleep too much.
• You mustn’t be so hasty.

“Not+Have to” means that there is no necessity to do something:

• The teacher is ill so I don’t have to go to school.
• You don’t have to listen to me since you look busy.
• They don’t have to come tonight.
• If she retires, she won’t have to work anymore.
• He doesn’t have to bring gifts every time he comes here.

 

Let’s do some exercises with what we have learned already. Fill the gaps with the proper words: must, have to, must not, not+have to.

 

1. You ____ call me in the afternoon tomorrow as I have work.
2. She ____ be so cold outside in the snow.
3. You ____ to be so formal. We’re friends now!
4. I ____ send my boss this email. It’s important.