• must = to do something that needs to be done
    • -> You must keep this a secret.
  • mustn’t = to be obligated no to do
    • -> You mustn’t tell anyone.
  • needn’t = to not have to
    • dá se nahradit don’t need to
      • ! don’t need to do X needn’t do
    • -> You needn’t tell Steve. I can tell him myself.
    • needn’t have done = to have done something that hasn’t been necessary to do
      • -> We needn’t have worried