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Modal Verbs - Lesson 203

Mustn't vs Don't Have To - Prohibition

Lesson 203 - learn modal verbs of prohibition: mustn't and don't have to: how to form it, when to use it, clear examples and a short video from a British English teacher.

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How to form and use the mustn't vs don't have to

Mustn't is a prohibition. Don't Have to is optional.

Mustn't talks about a prohibition in the present or future. A rule. A norm. A strong obligation. Something that is not permitted.
For example: You must not smoke in a petrol station. It is prohibited by law.
You mustn't be rude to your parents, you must show more respect.
People mustn't eat too much sugar and salt if they wish to live a long life.

Don't have to talks about things that are not necessary, but that you can do if you want. The action is possible and optional, but not obligatory.
For example: You don't have to donate money to charity, but it is a good thing to do.
You don't have to come to the party, but I would really appreciate it if you did come.
You don't have to do it my way, but if you do it your way, you are going to have trouble.


The following video explains the difference between Mustn't and Don't Have to:

Watch the video lesson

Video transcript

Hi there. Mustn't and don't have to. Notice in the positive, must and have to are very similar. In the negative they are completely different. You must not, a prohibition. You don't have to. It's not necessary. It's optional. It's voluntary. OK. So, you mustn't eat poison, or you will die. You don't have to eat chocolate, but you can eat chocolate if you want. So, you don't have to, you can if you want. Erm.. people work Monday to Friday and sometimes they work on Saturday. Sometimes it's voluntary and sometimes it's not. OK. So, if it's voluntary you don't have to work on Saturday, but you can if you want. It's that simple. You mustn't, it's prohibited. You don't have to, you can if you want, it's possible but it's not necessary. In another video I... we will look at mustn't and don't have to in the past, because notice mustn't is only for present and future. So thanks for watching and I'll see you in another video. Bye for now.

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This lesson is part of our free English Modal Verbs course. Work through the series in order, or jump to the tense or structure you need next.

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