must

I strong UK [mʌst] / US weak UK [məst] / US modal verb ***

Summary:

Must is usually followed by an infinitive without "to": You must stop at the red light. Sometimes must is used without a following infinitive: We will act alone if we must.
Must does not change its form, so the third person singular form does not end in "-s": She must be asleep. Questions are formed without "do": Must we wear our uniforms? Must can be used in question tags: We mustn't be late, must we? The negative form must not is used for saying that something should not be done. This is often shortened in conversation or informal writing to mustn't: You mustn't use the office phone for private calls. For saying that it is not necessary to do something not have to, not need to, or needn't is used: Children don't have to pay to go in. ♦ You don't need to take the test. There is no infinitive form of must, so to have to is used instead: I didn't expect to have to do my own cleaning. There is no past tense, but had to is used for saying that something was necessary in the past: We had to show our passports. Must have followed by a past participle can be used for saying that you believe something happened in the past: They must have missed the train. When indirect speech is introduced by a verb in the past tense, must can be used as a past tense: She said that I must come immediately. There is no future tense, but must can be used for saying that someone should do something in the future: You must be here at nine o'clock tomorrow morning. For saying that something will be necessary in the future will have to can be used: Graham will have to sleep on the sofa.

1) used for saying that you think something is probably true because nothing else seems possible

You must be tired after your long journey.

There must be some mistake – no one called Shaw lives here.

They must have got lost or they'd be here by now.

I must have fallen asleep.

2) used for saying that it is necessary or important to do something

Tomato plants must be watered regularly.

People must realize that there are limits to what we can do.

I've told you the truth. Must I keep repeating it?

We mustn't be late.

a) used for ordering someone to do or not do something

You must answer all the questions.

Shayler was warned that he must not publish the allegations.

b) used for saying that it is your duty to do something

We must defend the freedom that our parents fought for.

3) used for suggesting to someone that they should do something because it would be enjoyable, interesting etc

You must come and visit us again some time.

You must see the Monet exhibition – it's really wonderful.

4) used for emphasizing that you intend to do something

I must introduce you to my brother.

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if you (really) must — spoken used for telling someone that it is all right to do something, even though you do not want them to

"I'm just going to finish this off first." "Go on then, if you must."

must you? — spoken used for telling someone that what they are doing annoys you

Must you rush around without looking where you're going?

what/why must...? — used for showing that you are unhappy or angry about a situation

Why must life be so damn complicated?

I forgot their daughter's name. What must they think of me?

See:

say I

II UK [mʌst] / US noun

- a must