| A |
Must and mustn't
You must do something = it is necessary that you do it:
- Don't tell anybody what I said. You must keep it a secret.
- We haven't got much time. We must hurry.
You mustn't do something = it is necessary that you do not do it (so don't do it):
- You must keep it a secret. You mustn't tell anyone. (= don't tell anyone)
- We must be very quiet. We mustn't make any noise.
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| B |
Needn't and don't need to
You needn't do something = it's not necessary to do it (but you can if you like):
- We've got plenty of time. We needn't hurry. (= it is not necessary to hurry)
- Joe can stay here. He needn't come with us. (= it is not necessary for him to come)
You can also use don't/doesn't need to:
Remember that we say don't need to do / doesn't need to do, but needn't do (without to).
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| C |
Needn't have (done)
Study this example situation:
Paul and Sue decided to go to a restaurant. They reserved a table. But the restaurant was almost empty. So they needn't have reserved a table.
They needn't have reserved a table. = They reserved a table, but this was not necessary.
Compare needn't (do) and needn't have (done):
- Everything will be OK. You needn't worry. (it is not necessary)
- Everything was OK. You needn't have worried. (you worried, but it was not necessary)
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| D |
Needn't have (done) and didn't need to (do)
He needn't have done something = he did it, but now we know that it was not necessary:
- Why did he get up at 5 o'clock? He needn't have got up so early. He could have stayed in bed longer.
He didn't need to do something = it was not necessary to do it. It doesn't matter whether he did it or not:
- He didn't need to get up early, so he didn't.
- He didn't need to get up early, but it was a beautiful morning, so he did.
He didn't have to ... is also possible in these examples.
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