English Grammar in Use – Unit 32: “Must, Mustn’t, Needn’t”

  • English Grammar Class
  • Coursebook: English Grammar in Use
  • Unit: 32
  • Topic: Modal Auxiliary Verb: “Must, Mustn’t, Needn’t”

Part 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.

Part 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 = We don’t need to hurry.
Remember that we say don’t need to do I doesn’t need to do, but needn’t do (without to).

Part C:

Needn’t have (done)

Study this example situation.

Hello, can I reserve a table for two, please?

We needn’t have reserved a table.

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)

Part 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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