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must

 
pronunciation:
muhst
features:
Word Combinations (verb), Note
part of speech: verb
definition 1: used to express necessity to do something; have to.
Humans must breathe in order to live.
definition 2: to be required to (do something) because of a command, rule, or law.
Children must attend school.
definition 3: used to express a command to do something or not to do something.
You can take a break, but you must be back in ten minutes.Employees must not use this machine without proper training.
definition 4: used to make a strong statement about something based only on logic, not knowledge.
That woman must be her sister. She looks just like her.He is not answering the phone, so he must be out.
Word CombinationsSubscriber feature About this feature
must or have to?
Have to and must share the meaning of necessity to do something. Have to is used more often in everyday conversation. Must is more often used in writing or in a formal situation. But for the meaning of must in a sentence such as You must be joking!, both have to and must are very common in conversation. You need to be careful, though, to choose between have to and must when your sentence uses not. In negative sentences, have to and must have different meanings, as you can see in the examples below.
Compare:
  • You have to leave tomorrow.
  • You must leave tomorrow.
  • You do not have to leave tomorrow. (It is not necessary for you to leave tomorrow. You can leave tomorrow if you want, or you can stay.)
  • You must not leave tomorrow. (You do not have permission to leave tomorrow.)