Needn't, don't need to and Don't have to

Question 1

NEED can be used as modal verb or ordinary verb.
As modal verb it doesn’t change the tense, or add “S”.

Answer 1

Ordinary verb:
I need to leave early. She needs a drink.
Modal verb (Without S)
You needn’t speak so loudly. She needn’t speak so loudly.

Question 2

As a modal verb, NEED is used in negative.

Answer 2

I’ve already cleaned the car, so you needn’t bother to do it.
I was very nervous before the interview, but I needn’t have worried-I got the job. (apply, concern, fear, involve, mean, panic)

Question 3

In questions, use NEED as an ordinary verb.

Answer 3

Formal: Need you go so soon?
Do you need to go so soon? Do you have to go so soon? (ordinary verb).

Question 4

NEED is rarely used in affirmative sentences.

Answer 4

FORMAL: We need have no fear for that.

Question 5

In formal written, NEED is used with hardly, never, only, nobody, no one.

Answer 5

The changes need only be small.
Nobody ever need know all about that.
They need never know about that.

Question 6

To give permission not to do sth.

Answer 6

You needn’t cut the grass. (you don’t need to cut the grass).

Question 7

A general necessity, use Don’t need to.

Answer 7

You don’t need to be over 18 to go to a nightclub.

Question 8

To say it is unnecessary to do sth.
Needn’t or don’t have to.

Answer 8

You needn’t whispers. (you don’t have to whispers).

Question 9

Use NEEDN’T when is the speaker who decide.

Answer 9

You needn’t come until 10 tomorrow morning.

Question 10

USE NEEDN’T or Don’t have to to say a thing is not necessarily true.

Answer 10

Volcanos needn’t erupt constantly to be considered active. (Don’t have to).
Nowadays it needn’t cost a fortune to have computers. (It doesn’t have to cost a fortune…).