Must / mustn’t /needn’t

A. Must     mustn’t     needn’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 anybody else. (= don’t tell anybody else)
• It’s essential that nobody hears us. We mustn’t make any noise.

 

‘You needn’t do something’ = it is not necessary that you do it, you don’t need to do it:

 

• You can come with me if you like but you needn’t come if you don’t want to. (= it is not necessary for you to come)
• We’ve got plenty of time. We needn’t hurry. (= it is not necessary to hurry)

 

B. Instead of needn’t, you can use don’t/doesn’t need to. So you can say:

• We needn’t hurry, or We don’t need to hurry.

 

Remember that we say ‘don’t need to do’, but ‘needn’t do’ (without to)

 

Needn’t and don’t need to are similar to don’t have to.

 

• We’ve got plenty of time. We don’t have to hurry.

 

C. Needn’t have (done)

Study this example situation:

 

George had to go out. He thought it was going to rain, so he decided to take the umbrella.

 

George: I think it’s going to rain. I’ll take the umbrella.

 

But it didn’t rain, so the umbrella was not necessary. So: He needn’t have taken the umbrella.

 

George: I needn’t have brought the umbrella.

 

‘He needn’t have taken the umbrella’ = He took the umbrella but this was not necessary. Of course, he didn’t know this when he went out.

 

Compare needn’t (do) and needn’t have (done):

 

• That shirt isn’t dirty. You needn’t wash it.
• Why did you wash that shirt? It wasn’t dirty. You needn’t have washed it.

 

D. Didn’t need to (do) and needn’t have (done)

I didn’t need to… = it was not necessary for me to… (and I knew this at the time):

 

• I didn’t need to get up early, so I didn’t.
• I didn’t need to get up early, but it was a lovely morning, so I did.

 

‘I needn’t have (done) something’ = I did something but now I know that it was not necessary:

 

• I got up very early because I had to get ready to go away. But in fact it didn’t take me long to get ready. So, I needn’t have got up so early. I could have stayed in bed longer.

 

EXERCISES

1 Complete the sentences using needn’t + one of these verbs:

ask   come   explain   leave   tell   walk

1. We’ve got plenty of time. We …needn’t leave… 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 something to eat. You …………………………………………… first.
5. We can keep this a secret between ourselves. We …………………………………………… anybody else.
6. I understand the situation perfectly. You …………………………………………… further.

 

2 Complete the sentences with must, mustn’t or needn’t.

1. We haven’t got much time. We  must hurry.
2. We’ve got plenty of time. We … needn’t…. hurry.
3. We have enough food at home so we ………………………….. go shopping today.
4. Jim gave me a letter to post. I………………………….. remember to post it.
5. Jim gave me a letter to post. I………………………….. forget to post it.
6. There’s plenty of time for you to make up your mind. You ………………………….. decide now.
7. You ………………………….. wash those tomatoes. They’ve already been washed.
8. This is a valuable book. You ……………………… look after it carefully and you ……………………….lose it.
9. ‘What sort of house do you want to buy? Something big?’  ‘Well, it………………………….. be big — that’s not important. But it………………………….. have a nice garden — that’s essential.’

 

3 Read the situations and make sentences with needn’t have.

1. George went out. He took an umbrella because he thought it was going to rain. But it didn’t rain.He needn’t have taken an umbrella,
2. Ann bought some eggs when she went shopping. When she got home, she found that she already had plenty of eggs. She ………………………………………………………………………………………………….
3. A friend got angry with you and shouted at you. You think this was unnecessary. Later you say to him/her: You ……………………………………………………………………………………………………………..
4. Brian had no money, so he sold his car. A few days later he won some money in a lottery. He…………………………………………………………………………………………………………………………………………………
5. When we went on holiday, we took the camera with us but we didn’t use it in the end………………………………………………………………………………………………………………………………………………….
6. I thought I was going to miss my train so I rushed to the station. But the train was late and in the end I had to wait 20 minutes. ………………………………………………………………………………..……………………….

 

4 Write two sentences for each situation. Use needn’t have in the first sentence and could have in the second (as in the example).

1. Why did you rush? Why didn’t you take your time? You needn’t  have rushed. You could have taken your time,
2. Why did you walk home? Why didn’t you take a taxi?………………………………………………………………..
3. Why did you stay at a hotel? Why didn’t you stay with us?…………………………………………………………..
4. Why did she phone me in the middle of the night? Why didn’t she phone me in the morning?…………………………………………………………………………………………………………………………………………………
5. Why did you leave without saying anything? Why didn’t you say goodbye to me?…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….