Must and Have to

In affirmative sentences, we can use ‘must’ to say what is necessary, and to give strong advice and orders to ourselves and others.

E.g. Plants must get enough light and water if they are to grow properly.

I really must stop smoking.

You must be here before eight o’clock tomorrow.

‘Must’ is common in emphatic sentences.

E.g. You really must come and see us soon.

In sentences about obligation with ‘must’, the obligation comes form the speaker. To talk about obligation that comes from ‘outside’ (for instance a regulation, or an order from somebody else), we usually prefer ‘have to’.

E.g. I have to work from nine to five.

In my job I have to travel a lot.

In questions, people use ‘must’ to ask about what the hearer thinks is necessary.

E.g. Must I clean all the rooms?

Why must you always leave the door open?

‘Must not’ is used to say that things should not be done, or to tell people not to do things.

E.g. The government mustn’t expect people to work for no money.

You mustn’t open this parcel until Christmas Day.

Note that ‘mustn’t’ is not used to say that things are unnecessary. This idea is expressed by ‘do not need to’ or ‘do not have to’.

E.g. You don’t need (don’t have) to get a visa to go to Scotland.

NB. There is a certain difference in the use of ‘must’ and ‘have to’ in British and American English. In American English ‘have to’ is more common, particularly in speech.

E.g. Must I clean all the rooms? (BrE)

Do I have to clean all the rooms? (AmE)

Plants must get enough light and water. (BrE)

Plants have to get enough light and water. (AmE)

Need

When ‘need’ is followed by another verb, it can have forms either of an ordinary verb or of a modal auxiliary verb. If it is an ordinary verb it has ‘-s’ in the third person singular and is followed by an infinitive with ‘to’. Questions and negatives are made with ‘do’. It is used to express general necessity or its absence. It means ‘require’.

E.g. Everybody needs to rest sometimes.

Do we need to reserve seats on the train?

You don’t need to pay for emergency calls in most countries.

‘Will need to’ can be used to talk about future obligations, and give advice for the future. It can make orders and instructions sound less direct.

E.g. You will need to fill in this form before you see the Inspector.

‘Need’ as a modal auxiliary is mostly used in negative sentences.

E.g. You needn’t reserve seats. There’ll be plenty of room.

‘Need not + perfect infinitive’ is used to say that somebody did something, but that was unnecessary – a waste of time. On the other hand, if we say that somebody ‘did not need to do something’, we say that it was not necessary and most probably it wasn’t done.

E.g. I needn’t have watered the flowers. Just after I finished it started raining.

It started raining, so I didn’t need to water the flowers.

Should and Ought to

‘Should’ and ‘ought to’ are very similar in meaning and can replace each other, though ‘should’ is much more frequent.

E.g. They ought to be more sensible, shouldn’t they?

They are both used to talk about obligation and duty and to give advice. They are less strong than ‘must’.

E.g. People should drive more carefully. (More polite than ‘People must …’)

‘Should’ and ‘ought to’ can be used with perfect infinitives to talk about unfulfilled obligations in the past. ‘Must’ is not used like this.

E.g. You should have been nicer to Annie. (NOT: You must have been …)

Shall

‘Shall’ is used in questions with ‘I/we’ to ask for instructions or decisions, to offer services and make suggestions.

E.g. What time shall we come and see you?

Shall we go out for a meal?

In contracts and other legal documents, ‘shall’ is often used with third-person subjects to refer to obligations and duties.

E.g. The hirer shall be responsible for the maintenance of the vehicle.

Be + Infinitive

This structure is used in formal style to talk about plans and arrangements, especially when they are official.

E.g. The President is to visit Nigeria next month.

We are to get a 10% wage rise in June.

I felt nervous because I was soon to leave home for the first time.

A perfect infinitive can be used to show that a planned event did not take place.

E.g. I was to have started work last week, but I changed my mind.

‘Be + passive infinitive’ is often used in notices and instructions.

E.g. This cover is not to be removed.

Note that this structure exists only in present and past tenses, not present perfect or future.

 

Unit 9