Page 19 - Grasp English B1 (Grammar Book)

Rules at School 3

Modals of obligation and prohibition in the present

We use must and have to to talk about something which is necessary or required. The requirement
consists of rules, laws or prohibition.
We must wait at the red light. You have to wait at the red light.
You must bring your books to school every day. You have to get up early.

We use mustn’t to talk about things that we aren’t allowed to do. It is against the law or rules. It also
expresses prohibition.
You mustn’t cross the street at the red light.

We use don’t have to to show that something is not necessary.
We don’t work on Saturdays, so you don’t have to come to the office.
You don’t have to take medicine any more because you are very well now.
We use can’t to show that something is prohibited or not permitted.
You can’t use drugs in this country.
You can’t use your mobile phone here.
You can’t bring your pet to the restaurant.

We use needn’t to show that something is not necessary.
We can use don’t have to instead of needn’t.
You needn’t buy any vegetables. We have got
a lot at home.
You don’t have to buy any vegetables. We have got
a lot at home.

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