Discussion:
Simi: My house is very near the motorway.
Riva: It must be very noisy.
You can use must to say that you believe something is certain:
- You’ve been traveling all day. You must be tired. (Traveling is tiring and you’ve been traveling all day, so you must be tired.)
- ‘Jim is a hard worker’. Jim? You must be joking. He doesn’t do anything.’
- Carol must get very bored in her job. She does the same thing every day.
- I’m sure Sally gave me her phone number. I must have it somewhere.
You can use can’t to say that you believe 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.
- They haven’t lived here for very long. They can’t know many people.
Study and structure:
| I/you/he (etc) | Must Can’t | Be (tired/hungry/at work etc) Be ( doing/going/joking etc) Do/get/know/have etc |
For the past we use must have (done) and can’t have (done):
- There’s nobody at home. They must have gone out
Situation:
Martin and Lucy are standing at the door of their friends house.
They have rung the doorbell twice, but nobody has answered. Luch says:
They must have gone out.
- I didn’t here the phone. I must have been asleep.
- ‘I’ve lost one of my gloves.’ You must have drooped it somewhere.
- Sue hasn’t contacted me. she can’t have got my message.
- Tom walked into a wall. He can’t have been looking where he was going.
Study and structure:
| I/you/he (etc) | Must Can’t | have | Been (asleep/at work etc.) Been (doing/looking etc.) Gone/got/known etc. |
You can use couldn’t have instead of can’t have:
- sue couldn’t have got my message.
- Tom couldn’t have been looking where he was going.
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