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7. Necessity: mustnt, neednt, etc.

FORM 9

1 Mustn't or needn't?

We use must to say that something is necessary.
You must be careful with those glasses.
I must remember my key.

Now compare mustn't and needn't.

MUSTN'T

We use mustn't ['masnt] to say that something is a
bad idea.
You mustn't drop those glasses. They'll break.
I mustn't forget my key, or I won't get in.
You mustn't wear your best clothes. You'll get
them dirty.

NEEDN'T

We use needn't when something is not necessary.

You needn't wash those glasses. They're clean.
We needn't make sandwiches. There's a cafe.
You needn't wear your best clothes. You can wear
what you like.

2 Don't have to and don't need to

We can use don't have to and don't need to when something is not necessary.
The meaning is the same as needn't.
You don't have to / don't need to wash those glasses. They're clean.
Mark doesn't have to / doesn't need to finish the report today. He can do it at the weekend.

For the past we use didn't.
The food was free. We didn't have to pay / We didn't need to pay for it.

3 Didn't need to or needn't have?

Daniel hadn't booked a seat, but luckily the train
wasn't fu ll. He didn't need to stand.

Trevor and Laura booked a table for dinner.
But the restaurant was empty. They needn't
have booked a table.

DIDN'T NEED TO

We use didn't need to when something was not
necessary. Standing was not necessary because
there were seats.
Mark didn't need to hurry. He had lots of time.
He drove slowly along the motorway.
We didn't need to go to th e supermarket because
we had plenty of food.

NEEDN'T HAVE

We use needn't have + a past participle for
something we did which we now know was not
necessary, e.g. booking a table.
Mark needn't have hurried. After driving at top
speed, he arrived half an hour early.
We needn't have gone to the supermarket. We
already had a pizza for tonight.

Sometimes we can use didn't need to when the action happened, even though it was not necessary.
Mark didn't need to hurry, but he drove at top speed. He likes driving fast.

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