Mustn’t (Must Not)

In negative sense, when talking about “must – should,” it means there is a prohibition.


You mustn’t smoke here. (It is forbidden to smoke here.)

You mustn’t leave the school if you don’t finish your schoolwork.

A scout mustn’t leave the camp unless he has got permission.

Needn’t / Don’t Have To / Don’t Need To (They have the same meanings)

In the present and future tense, when we don’t have to do something:


I needn’t worry about you. (I don’t need to worry about you.)

We needn’t wear gloves unless it snows.

You needn’t / don’t have to wear a suit tonight.

Didn’t Need To / Didn’t Have To

In the past when we didn’t have to do something:


He didn’t need to wear a suit last night.

She didn’t need to / didn’t have to write a formal letter because they required an informal one.

Mike didn’t need to get a taxi because his brother gave him a lift.

You can use these expressions to convey prohibitions or lack of necessity in different tenses.

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