Unit 28. Must and can't

We use must to say that we feel sure something is ture.

• You've been traveling all day. You must be tired.
  (Travelling is tiring and you've been travelling all day, so you must be tired)
• Carol must get very bored in her job. She does the same thing every day.

We use can't to say that we feel sure something is nt possible.

• You've just had lunch. You can't be hungry already.
  (People are not normally hungry just after eating a meal. You've just eaten, so you can't be hungry.)
• They haven't lived here for very long. They can't know many people.

For the pas we use must have (done) and can't have (done). 

George is outside his friends' house.
He has rung the doorbell three times but nobody has answered.
They must have gone out.
(otherwise they would have answered)

• The phone rang but I didn't hear it. I must have been asleep.
• I've lost one of my gloves. I must have dropped it somewhere.

Couldn't have... is possible instead of can't have...

• She couldn't have seen me.
• Tome couldn't have been looking where he was going.