Can’t haveis also possible, but it is much less common than couldn’t have.

Certainty

Certainty about the Present

When making deductions about the present, we use mustif we are sure something is true and can'tif we are sure that something is impossible.

For example, if you see this guy, you can say:

· He mustbe a chef.

(we are very certain, because of his uniform and what he is doing)

· He can’tbe a policeman.

(we are very certain he is NOT a policeman)

Carla works every day from 9 AM to 5 PM. Right now it’s 10:30 AM, so…

· She mustbe at work.

· She can'tbe at home.

Put it into practice!

You'll see five pictures accompanied by sentences. For each one, fill in the blank with must(if you think it is true) or can't(if you think it's not possible).

He be a vegetarian. They be in love.

You studied all night. You be exhausted.

That be right…

She love her cat.

Certainty about the Past

When we consider some present evidence and draw a reasonably certain conclusion about what happened in the past, we use must haveand couldn't haveplus the past participle of the verb.

must have + past participle

when we draw the conclusion that something DID happen

· Sheila got a tan. She must have spenta lot of time in the sun lately.

· There was one banana left, but now it's gone. My husband must have eatenit.

must not have + past participle

when we draw the conclusion that something did NOT happen

· The car is still dirty. Paul must not have washedit yet.

· He barely touched his lunch. He must not have beenhungry.

couldn't have + past participle

when we are certain that something was IMPOSSIBLE

· Martha couldn't have takenyour notebook; she wasn't even in class yesterday.

· The cookies are gone. But Eric couldn't have reachedthe cookies on the top shelf; he must have askedhis older brother to get them.

Can’t haveis also possible, but it is much less common than couldn’t have.

Here’s an example that illustrates the difference between must not haveand

couldn’t have:

· I don’t see the report here – she must not haveprinted it out.

(we draw the conclusion that she did not do it)

· The printer’s been broken for the past week, so she couldn’t haveprinted out the report.

(we know it was IMPOSSIBLE for her to do it)

Date: 2015-12-11; view: 1269