May and Might

‘May’ and ‘might’ can both be used to ask for permission. They are more formal than ‘can’ and ‘could’.

E.g. May I borrow your car? – No, I’m afraid you may not.

I wonder if I might have a little more cheese. (very formal)

‘Might’ can be used to criticize. ‘Might + perfect infinitive’ is used to talk about the past.

E.g. You might phone Mother. She is so worried. – Ты мог бы и позвонить маме.

She might have told me she was going to stay out all night. – Она могла бы и сказать мне , что собирается …

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.