Need as a modal auxiliary verb

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.

§  One needs to be punctual.

§  Everybody needs to be loved. 

§  He needed some more time to decide the question.

Questions and negatives are made with do.

§  Do you need to go now? 

§  I don't need to talk to him. 

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.

§  You need not work today. 

§  Need I go now? 

§  Need we reserve seats? 

§  He need only say what he wants and it will be granted.

§  I need hardly add that you are always welcome.

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

§  He need not wait. (NOT He needs not wait.) 

§  You need not come. 

Questions and negatives are made without do.

·         Need I come again? (NOT Do I need come again?)

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.

§  You need not work today. (Auxiliary - Particular occasion) 

§  You don't need to work on Sundays. (Ordinary - habitual thing) 

§  You need not pay for this call. (Auxiliary - Particular occasion) 

§  In most countries, you don't need to pay for emergency calls. (Ordinary - general thing) 

Need is usually used in questions without 'not'.

·         Need I wait any longer?

·         Need he come again?

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.

§  They need not have come all this way. (= They came all this way, but it was not necessary.)

§  We need not have waited for his approval. (= We waited for his approval, but that was not necessary.)

§  You need not have bought a new car.

§  You need not have paid for that call.

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:

§  I need not have bought it. (=I bought it, but it was not necessary.) 

§  I didn't need to buy it. (=It was not necessary for me to buy it.) 

Need + participle

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

§  Your hair needs washing. (= Your hair needs to be washed.)

§  The carpet needs cleaning. (= The carpet needs to be cleaned.) 

§  The roof needs repairing. 

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

§  You need your hair cutting/cut. 

§  You need your car cleaned.