032 : must / mustn’t / needn’t

   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.

 

 

   B   

Needn't(영) and don't need to(미)

 

 

You don't need to do something = it's not necessary to do it (but you can if you like):

• We've got plenty of time. We don't need to hurry. (= it is not necessary to hurry)
• Joe can stay here. He don't need to come with us. (= it is not necessary for him to come)

 

 

You can also use needn't :  

•   We needn't hurry.

 

 

Remember that:

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

 

 

   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)

 

 

   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.

 

 

 

 

 (American English -> Appendix 7) 

 

BRITISH You can use needn't or don't need to: We needn't hurry.  or  We don't need to hurry.

AMERICAN Needn't is unusual. The usual form is don't need to: We don't need to hurry.