4.216 'must'

'Must' is used in three common ways to talk about the importance of doing something.

You use 'must' with 'you' or 'we' to urge someone to do something, because you feel it is important. 'Must not' is used to urge someone not to do something.

• You must come at once.
• We must accept the truth about ourselves.
• You must not worry.
• You mustn't let her suffer for it.

You use 'must' to say that something is required by a rule or law.

• People who qualify must apply within six months.
• European Community standards must be met.

You use 'must' to say that it is necessary that something happens or is done, in order that something else can happen.

• Meadows must have rain.
• To identify a poison you must be able either to carry out a chemical analysis or observe the poison at work on the victim.

'Have to', 'have got to', and 'need to' can be used instead of 'must' to talk about the importance of doing something. This is explained in paragraphs 4.248 and 4.249.