Main points

* You use `need to’ to talk about necessity.

* You use `don’t have to’, `don’t need to’, `haven’t got to’, or `needn’t’ to say that it is not necessary to do something.

* You use `needn’t’ to give someone permission not to do something.

* You use `need not have’, `needn’t have’, `didn’t need to’, or `didn’t have to’ to say that it was not necessary to do something in the past.

1 You can use `need to’ to talk about the necessity of doing something.
You might need to see a doctor.
A number of questions need to be asked.

2 You use `don’t have to’ when there is no obligation or necessity to do something.
Many women don’t have to work.
You don’t have to learn any new typing skills.

You can also use `don’t need to’, `haven’t got to’, or `needn’t’ to say that there is no obligation or necessity to do something.
You don’t need to buy anything.
I haven’t got to go to work today.
I can pick John up. You needn’t bother.

3 You also use `needn’t’ when you are giving someone permission not to do something.
You needn’t say anything if you don’t want to.
You needn’t stay any longer tonight.

4 You use `need not have’ or `needn’t have’ and a past participle to say that someone did something which was not necessary. You are often implying that the person did not know at the time that their action was not necessary.
I needn’t have waited until the game began.
Nell needn’t have worked.
They needn’t have worried about Reagan.

5 You use `didn’t need to’ to say that something was not necessary, and that it was known at the time that the action was not necessary. You do not know if the action was done, unless you are given more information.
They didn’t need to talk about it.
I didn’t need to worry.

6 You also use `didn’t have to’ to say that it was not necessary to do something.
He didn’t have to speak.
Bill and I didn’t have to pay.

7 You cannot use `must’ to refer to the past, so when you want to say that it was important that something did not happen or was not done, you use other expressions.

You can say `It was important not to’, or use phrases like `had to make sure’ or `had to make certain’ in a negative sentence.
It was important not to take the game too seriously.
It was necessary that no one was aware of being watched.
You had to make sure that you didn’t spend too much.
We had to do our best to make certain that it wasn’t out of date.