1. You haven’t got much time. You must hurry.
2. You can tell John what I said but he must keep it a secret .

You mustn’t do means that it is necessary that you do not do something. Let’s see the following examples.

1. The baby is asleep. You mustn’t talk loudly.
2. This is a non-smoking area. You mustn’t smoke here.

You needn’t do means that it is not necessary that you do something. Let’s see the following examples.

1. I can hear you quite clearly . You needn’t talk loudly. (= It is not necessary to talk loudly.)
2. You’ve got plenty of time. You needn’t hurry. (=It is not necessary to hurry.)

Needn’t do can be replaced with doesn’t/don’t need to do. So, the two sentences above can be rewritten this way:

1. I can hear you quite clearly. You don’t need to talk loudly.
2. You’ve got plenty of time. You don’t need to hurry.

We use needn’t have done to say that it was not necessary to do (in the past). Let’s see the following examples.

1. Achmad wanted to catch a plane. He left home late, so he hurried to the station. But the train was also late – it didn’t leave until 20 minutes after Achmad arrived at the station. So, Achmad needn’t have hurried.
2. Jane bought some sugar but when she got home she found that she already had a lot of sugar. So she needn’t have bought any sugar.

Didn’t need to is different from needn’t have.

We use didn’t need to  to say that an action was unnecessary. This was known at the time of the action.  Let’s see the following examples.

1. I didn’t need to go, so I didn’t go.
2. I didn’t need to go but I decided to go anyway.

When we use needn’t have, it was not known at the time that the action was not necessary. Let’s see the following example.

1. I needn’t have gone. (= I went – this was unnecessary, but I didn’t know at the  time that it was unnecessary.)

In this exercise you have to complete the sentences with needn’t or mustn’t !

1. Jack gave me a letter to post. I ………..forget to post it.
2. “Do you want me to wait?” “No, It’s okay. You ………..wait.”
3. This ring is very valuable. You ……..lose it.
4. You …….come if you don’t want to.
5. We still have enough eggs. We ……..buy any.

Exercise II

Answer the following questions. Ask and answer with your partner if possible.

1. Write three things you mustn’t do when you do the school exam.
2. Mention three things you needn’t do to enjoy your life.
3. Tell us/me a few things you must always do in the morning.
4. Can you tell your Mom a few things she needn’t do every day.
5. Tell your brother or sister a few things he/she mustn’t do in her social media account.

Answers

Exercise I

1. Jack gave me a letter to post. I mustn’t forget to post it.
2. “Do you want me to wait?” “No, It’s okay. You  needn’t wait.”
3. This ring is very valuable. You mustn’t lose it.
4. You needn’t come if you don’t want to.
5. We still have enough eggs. We needn’t buy any.

Exercise II

Different answers are welcome.

1. I mustn’t cheat, talk, make noise.
2. First, I needn’t worry too much about anything; then, I needn’t have bad prejudice; Also, I needn’t be too ambitious.
3. I must get up early, take a shower, have breakfast, perform sholat.
4. She needn’t cook every day, worry about me too much, work too hard, clean the house every day.
5. He/she mustn’t reveal his/her private life too much, communicate with strangers, say inappropriate things.

Download the exercises in Google Drive.