• Modals of Deduction

• 
• Use a modal of deduction when you are sure about something.
  

  
  

  Use must or must not* when you are 100% certain about something and have evidence.

  -Tasha must be rich.  She has a private airplane. 

  (We are sure she is rich because she has her own airplane.)

  -John never eats eggs. He must not like them.

  (We are sure he doesn't like eggs because he never eats them.)

  
  

  Use can't when something is not true or not possible.

  -She can't be at work.  I saw her at the mall ten minutes ago.

  (It is impossible for her to be at work right now.)
•  Click on the play button to hear the audio

• That restaurant must be popular.  There's always a really long line.	Sam doesn't like anything scary.  He must not watch horror movies.
  I just bought that box of chocolates yesterday. It can't be empty already!	They can't make it before the concert starts.  They missed the train.

• *Be careful! Do not use mustn't for deductions.
• 
  

Source : Alison