UNIT 28. Must and can't

A. Study this example:

We use must to say that we feel sure something is true:

* You've been travelling all day. You must be tired. (Travelling is tiring and you've been travelling all day, so you must be tired.)

* 'Jim is a hard worker.' 'Jim? A hard worker? You must be joking. He's very lazy.'

* 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 not 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.)

* Brian said he would definitely be here before 9.30. It's 10 o'clock now and he's never late. He can't be coming.

* They haven't lived here for very long. They can't know many people.

Study the structure:

I/you/he (etc.) must/can't be (tired/hungry/at work etc.)

I/you/he (etc.) must/can't be (doing/coming/joking etc.) do/go/know/have etc.

I/you/he (etc.) must/can't do/go/know/have etc.

B. For the past we use must have (done) and can't have (done). Study this example:

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.

* Jane walked past me without speaking. She can't have seen me.

* Tom walked straight into a wall. He can't have been looking where he was going.

Study the structure:

I/you/he (etc.) must/can't have been (asleep/at work etc.)

I/you/he (etc.) must/can't have been (doing/working etc.)

I/you/he (etc.) must/can't have done /gone/known/had etc.

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

* She couldn't have seen me.

* Tom couldn't have been looking where he was going.

EXERCISES

Put in must or can't.

1. You've been travelling all day. You must be very tired.

2. That restaurant --- be very good. It's always full of people.

3. That restaurant --- be very good. It's always empty.

4. You're going on holiday next week. You --- be looking forward to it.

5. It rained every day during their holiday, so they --- have had a very nice time.

6. Congratulations on passing your exam. You --- be very pleased.

7. You got here very quickly. You --- have walked very fast.

8. Bill and Sue go away on holiday very often, so they --- be short of money.