UNIT 27 Must (have) and can't (have)
A. Study this example situation:
Liz is a very good player, and not many players beat her. But yesterday she played against Bill and Bill won. So:
Bill must be a very good player (otherwise he wouldn't have won)
We use must to say we are sure that something is true:
- You've been traveling all day. You must be tired. (= I sure that you are am tired.)
- I hear that your exams are next week. You must be studying very hard right now. (= I am sure that you are studying.)
- Carol knows a lot about films. She must like to go to the movies. (= I am sure she likes to go to the movies.)
We use can't to say that think something is impossible:
- You just had dinner. You can't be hungry already. (= It is impossible that you are hungry.)
- Tom said that he would be here ten minutes ago, and he is never late. He can't be coming.
be tired/hungry, etc. I/you/he (etc.) {must} be studying/ waiting/coming, etc.
{can't} know/like, etc.
B. For the past we use must have (done) and can't have (done). Study this example:
We went to Roy's house last night and rang the doorbell. There was no answer.
He must have gone out (otherwise he would have answered).
- The phone rang, but I didn't hear it. I must have been asleep
- I made a lot of noise when I came home. You must have heard me.
- She passed me on the street without speaking. She can't have seen me.
- Tom walked into the wall. He can't have been looking where he was going.
Study the structure:
{must} {been asleep/tired, etc.
I/you/he (etc.) { } have {been looking/waiting, etc
{can't} {gone/done/seen/heard, etc.
"couldn't have (done)" is possible instead of "can't have (done)":
- She couldn't have seen me.
- He couldn't have been looking where he was going.
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