Modals – deductions about the past 14.4.2021

Do you know how to use modal verbs to show how certain you are about past events?

Look at these examples to see how must, might, may, could, can't and couldn't are used in the past.

An earthquake? That must have been terrifying!
We don't know for sure that Alex broke the coffee table. It might have been the dog.
How did she fail that exam? She can't have studied very much.

We can use modal verbs for deduction – guessing if something is true using the available information. The modal verb we choose shows how certain we are about the possibility. This page focuses on making deductions about the past.

must have
We use must have + past participle when we feel sure about what happened.
Who told the newspapers about the prime minister's plans? It must have been someone close to him.
The thief must have had a key. The door was locked and nothing was broken.
Oh, good! We've got milk. Mo must have bought some yesterday.

might have / may have
We can use might have or may have + past participle when we think it's possible that something happened. 
I think I might have left the air conditioning on. Please can you check?
Police think the suspect may have left the country using a fake passport.
May have is more formal than might have. Could have is also possible in this context but less common.

can't have / couldn't have 
We use can't have and couldn't have + past participle when we think it's not possible that something happened.
She can't have driven there. Her car keys are still here.
I thought I saw Adnan this morning but it couldn't have been him – he's in Greece this week.

On page 75 in you book do the exercise 4a, 4b, 4c, 4d.

Modals – deductions about the present

Look at these examples to see how must, might, may, could and can't can be used.

That must be the main entrance. I can see people queuing to get in.
I've lost my keys. They might be at work or they could be in the car.
You can't be bored already! You've only been here five minutes.

We can use modal verbs for deduction – guessing if something is true using the available information. The modal verb we choose shows how certain we are about the possibility. This page focuses on making deductions about the present or future. 
must
We use must when we feel sure that something is true or it's the only realistic possibility.
This must be her house. I can see her car in the garage.
He must live near here because he always walks to work.
Come inside and get warm. You must be freezing out there!
might, may, could
We use might, may or could to say that we think something is possible but we're not sure. 
She's not here yet. She might be stuck in traffic.
He's not answering. He could be in class.
We regret to inform you that some services may be delayed due to the bad weather.
They all have the same meaning, but may is more formal than might and could.
can't
We use can't when we feel sure that something is not possible.
It can't be far now. We've been driving for hours.
She can't know about the complaint. She's promoted him to team leader.
It can't be easy for him, looking after three kids on his own.
Note that these verbs, like all modal verbs, are followed by an infinitive without to.