[Azar] 의무, 필요(obligation and necessity)

• must와 have to 모두 필요를 나타낸다.
  
  All applicants must take an entrance exam.
  All applicants have to take an entrance exam.
  
  
• must보다는 have to가 더 널리 쓰인다. must는 have to보다 강한 의미, 즉 긴박감이나 중요성를 나타낸다.
  
  I'm looking for Sue. I have to talk to her about our lunch date tomorrow.
  Where's Sue? I must talk to her right away. I have an urgent message for her.
  
  
• have got to는 구어체에서 have to의 의미로 쓰인다.
  
  I have got to go now. I have a class in ten minutes.
  
  
• 과거의 필요를 나타낼 때는 had to를 쓰며, must의 과거형은 없다.
  
  I had to study last night.
  
  
• must not은 금지를 뜻하며, don't have to는 그럴 필요가 없다는 것을 나타낸다.
  
  Tomorrow is a holiday. We don't have to go to class.
  You must not tell anyone my secret. Do you promise?