English Grammar in Use With Answers » Unit 32: Must / mustn't / needn't

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.

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 / doesn't need to do, but needn't do (without to).

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)

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.

32.1 Which is correct?

  1. We haven't got much time. We must / mustn't hurry.
    • must
    • mustn't
  2. We've got plenty of time. We mustn't / don't need to hurry.
    • mustn't
    • don't need to
  3. I have to talk to Gary. I must / mustn't remember to call him.
    • must
    • mustn't
  4. I have to talk to Gary. I mustn't / needn't forget to call him.
    • mustn't
    • needn't
  5. There's plenty of time for you to make up your mind. You mustn't / don't need to decide now.
    • mustn't
    • don't need to
  6. We needn't / mustn't wash these tomatoes. They've already been washed.
    • needn't
    • mustn't

32.2 Complete the sentences. Use needn't + one of these verbs:

  • ask
  • come
  • explain
  • leave
  • walk
  1. We've got plenty of time. We yet.
  2. I can manage the shopping alone. You __________ with me.
  3. We __________ all the way home. We can get a taxi.
  4. Just help yourself if you'd like more to eat. You __________ first.
  5. I understand the situation perfectly. You __________ further.

32.3 Write two sentences for each situation. Use needn't have in the first sentence and could have in the second (as in the example). For could have, see Unit 27.

  1. Why did you rush? Why didn't you take your time?
    (1) .
    (2) .
  2. Why did you walk home? Why didn't you take a taxi?
    (3) __________ .
    (4) __________ .
  3. Why did you stay at a hotel? Why didn't you stay with us?
    (5) __________ .
    (6) __________ .
  4. Why did she phone me in the middle of the night? Why didn't she wait until the morning?
    (7) __________ .
    (8) __________ .
  5. Why did you shout at me? Why weren't you more patient?
    (9) __________ .
    (10) __________ .
  6. Why did you leave without saying anything? Why didn't yo u say goodbye to me?
    (11) __________ .
    (12) __________ .

32.4 Correct the sentences where necessary.

  1. We have plenty of time. We don't need hurry.
  2. You must keep it a secret . You mustn't tell anybody else.
    __________
  3. I'll be all right. You needn't to worry about me.
    __________
  4. You mustn't wait for me. You go on and I'll join you later.
    __________
  5. You don't need to keep these emails. You can delete them.
    __________
  6. I needn't have gone out, so I stayed at home.
    __________
  7. I needn't have bought eggs. We had some already.
    __________

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