MUST, MUSTN’T, NEEDN’T

1. 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.

2. 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 hurrry.

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

3. 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)

4. 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.