Must is one of the less commonly used modal verbs in American English which may be due to how direct the verb is. Must is used to describe certainty in how others should act. Let’s look at some example sentences:

  • You must sign the contract!
  • You must listen to your mother!

Must has a similar meaning to ‘(you) have to’. It’s often replaced with ‘have to’ which is just as direct, but less formal.