Had better

Had better refers to the immediate future. It is followed by an infinitive without to. It is a strong advice. We use it to tell people what to do.

§  You had better consult a doctor.

§  You had better apologize. 

§  We had better hurry up. We are already late. 

Had better sometimes suggests a threat and is not used in polite requests.

§  You had better tell them soon. If you don't, there will be trouble. 

§  You had better mend your ways. 

To make negative forms, we put not between had better and infinitive.

§  You had better not irritate him. 

Should, ought to, must

Should and ought have similar meanings. They are both used to talk about obligation, and to give advice or instructions.

·         We should respect our parents.

·         We ought to respect our parents.

·         You should stop smoking.

·         You ought to stop smoking.

Must is stronger than should and ought.

§  You must stop smoking. (A command.)

§  You should/ought to stop smoking. (A piece of advice.)

Must expresses certainty. Should/ought to expresses probability.

§  He must be home now. (It is certain.) 

§  He should be home now. (It is probable.) 

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. 

Ought to

Ought is a modal auxiliary verb. There is no -s in the third person singular.

·         She ought to understand. (NOT She oughts to ...)

Ought is different from other auxiliary verbs. It is used with to

§  We ought to respect our parents. 

§  We ought to help the poor. 

Note that to is dropped in question tags.

§  You ought to love your country, ought not you? (NOT...ought not you to.) 

Ought does not have infinitives (to ought) or participles (oughting, oughted). Questions and negatives are made without do.

§  Ought we to help them? (NOT Do we ought to ...)

§  You ought not to go now. 

Ought is rarely used in questions and negatives; should is generally used instead. A structure with think ... ought is also common.

·         We ought to help them, shouldn't we? (More natural than ought not we?)

·         Do you think I ought to consult a doctor? (More natural than Ought I to consult a doctor?)

·         Should we tell her? (Less formal than Ought we to tell her?)

Ought: Meaning

Ought expresses duty, necessity, desirability and similar ideas. It is often used to advise people - to tell them that they have a duty to do things. The meaning is similar to should

§  You ought to attend office regularly. (Duty) 

§  We ought to help the needy. (Moral obligation) 

§  We ought to buy some furniture. (Necessity) 

Ought is not as forceful as must.

Uses

To express probability

Ought can express logical probability.

§  If he started an hour ago, he ought to be here soon. 

Ought to have + past participle

When ought refers to past time, it is followed by the perfect infinitive. This structure can be used to talk about things which were supposed to happen but did not.

·         I ought to have written to my parents, but I forgot. 

·         You ought to have invited her to your party. 

This structure can also be used to make guesses.

·         It is ten o'clock. He ought to have reached home.

Ought not to have can be used to talk about things that happened unnecessarily.

§  We ought not to have wasted so much time over it. 

§  We have done things that we ought not to have done. 

§  We have left undone things that we ought to have done. 

Difference between must and have to

Both must and have to can be used to express the conclusion that something is certain. Note that have to is more common in American English.

·         He must be mad to do this. (OR He has to be mad to do this.)

·         You must be joking. (You have got to be joking.)

Conclusions about the past are usually expressed with must followed by the perfect infinitive (have + past participle).

·         I hear you have been to Australia. That must have been interesting.

Necessity

Must and have to can both be used to talk about necessity. In American English, have to is more common.

·         We must/have to build up a strong army to defend the country.

Obligation

Both must and have to can be used to talk about obligation. In American English have to is the normal form. British English often makes a distinction between them. Must is used mostly to talk about the feelings and wishes of the speaker and hearer. Have (got) to is used mostly to talk about obligations that come from 'outside' - for example from laws, regulations, agreements and other people's orders.

Compare:

·         I must stop smoking. (= I want to stop smoking.)

·         I have to stop smoking. (= Doctor has asked me to stop smoking.)

·         You really must go to church next Sunday. (I am telling you to.)

·         Catholics have to go to church on Sundays. (Their religion tells them to.)

Will have to is used to talk about future obligation, but have (got) to is preferred when arrangements for the future have already been made.

·         When you leave school you will have to find a job. (Future obligation)

·         I have got to go for a job interview tomorrow. (It is already arranged.)

Had to is used to talk about past obligation. Must is used with the perfect infinitive (have + past participle) to express certainty about the past.

·         Mary isn't in her office. She had to go home. (= It was necessary for her to go home.)

·         Mary isn't in her office. She must have gone home. (= It seems certain that she has gone home.)

Must not and do not have to/ have not got to have quite different meanings. Must not is used to tell people not to do things; do not have to/ have not got to is used to say that there is no obligation.

·         You must not tell him. (= Don't tell him.)

·         You don't have to tell him. (= You can if you like but it is not necessary.)

Must as an auxiliary verb

To express a conclusion

Must can be used to express the conclusion that something is certain or highly possible.

·         If A is bigger than B, and B is bigger than C, then A must be bigger than C.

·         There is the doorbell. That must be the postman.

Must in questions and negatives

Must is not often used to express certainty in questions and negative clauses. In questions we use can.

·         Somebody is knocking at the door. Who can it be? (NOT Who must it be?)

In negative clauses we generally use cannot/can't to say that something is certainly not the case.

·         It can't be your mother. She is in New York.

However, mustn't is normal in question tags after must, and in negative questions.

·         It must be nice to be a bird, mustn't it?

To express necessity

Must is often used in affirmative sentences to say what is necessary, and to give strong advice and orders to ourselves and other people.

·         We must get up early and start on our way.

·         We must build a strong army to defend the country.

·         I must stop smoking.

Must can be used in questions to ask about what the hearer thinks is necessary.

·         Must I go now?

In American English, have to is more common.

·         Do I have to go now?

Must not or mustn't is used to say that things should not be done, or tell people not to do things.

·         You must not open this parcel until Christmas day.

·         You must not lie.