Need as a modal auxiliary verb

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Need is used both as an ordinary verb and as an auxiliary verb.

As an ordinary verb

As an ordinary verb need is used in the sense of 'require'. It has the usual forms needs and needed. Ordinary need is followed by an infinitive with to.

Questions and negatives are made with do.

As an auxiliary verb

The auxiliary form of need is used mainly in questions and negatives. It is also used after negative words like hardly and only.

The auxiliary need is followed by an infinitive without to. It has no -s in the third person singular.

Questions and negatives are made without do.

Note that the auxiliary form of need is rare in American English.

Points to be noted

The auxiliary need is mainly used to ask for or give permission. It is not used to talk about habitual or general things.

Need is usually used in questions without 'not'.

If the answer is in the negative, you should say - 'No, he need not' or 'No, you need not'. But if the answer is in the positive, you should say - 'Yes, he must' or 'Yes, you must'. The opposite of need not in such a context is not need but must.

Need not + perfect infinitive

The structure need not + perfect infinitive can be used to say that somebody did something, but that was unnecessary.

Note that need not have does not mean the same as did not need to. When we say that somebody did not need to do something, we are simply saying that it was not necessary (whether or not it was done).

Compare:

Need + participle

In British English it is possible to use an -ing form after need. It means the same as a passive infinitive.

A structure with need + object + present/past participle is also possible in some cases.

Sections in this article

Modal Auxiliary Verbs
Can
May and Can: differences
Could
May
Might
Will
Would
Shall
Should
Should: other uses
Must
Must: uses
Must and have to: The Difference
Ought to
Need
Had better
Should, Ought and Must: The difference