modal verbs for speculation and deduction

Past modals

Míriam Tomàs

Logical assumptions and deductions

How can we express certainty, probability or speculation?

Let’s put on the thinking cap

must

You have been practising all day,

you must be exhausted!

must

Sean and Jennie must be going out again. I’ve seen them talking very lovey-dovey, you know.

Logical assumptions and deductions

Must:

▪ is used in affirmative sentences.

▪ states something about which you are certain that is true.

Modal verbs and different tenses

We can use modal verbs with different combinations of verbs to change the time of the actions.

must



must



Infinitive = present speculation

must


Infinitive + gerund (continuous) = in progress at the time of speaking

must


must

I must have left my phone at Anna’s. I definitely remember having it there.

must

I must have left my phone at Anna’s. I definitely remember having it there.

Have + past participle = speculation about the past

Can’t and couldn’t

What you say about Claire and Jake can’t be true! They’re so good together it’s impossible they’re going to break up.

Someone’s been at home, but it can’t have been James, he was at work.


You couldn’t have seen their faces. It was too dark.


Couldn’t = when the speculation is about the distant past


▪ Can’t and couldn’t are used in negations and express negative logical assumptions. That is to say, you use them when you’re certain that something is not true or real.

Monsters can’t be real!


▪ Can’t and couldn’t are the opposite of must. So we don’t say:

Monsters mustn’t be real!

but:

Monsters can’t be real!

Infinitive = speculation about the present


What you say about Claire and Jake can’t be true! They’re so good together it’s impossible they’re going to break up.

Someone’s been at home, but it can’t have been James, he was at work.


Have + past participle = speculation about the past

The children can’t be studying. I can hear them gossiping.


Infinitive + gerund = speculation about an action in progress at the

time of speaking

Possibility and probability

They might have been a perfect match, but something got in their way.

May and might

Someone might have stolen your wallet when you got off the train.

May and might

He hasn’t arrived yet. I may have given him the wrong directions.

May and might

We use may and might when we think it’s possible that

something’s happened or is true.

May and might

We’re not 100% sure!

He hasn’t arrived yet. I may have given him the wrong directions.

He might be lost.

He might be looking for the right directions.

May and might

Different tenses can also be used:

Infinitive presentHave + past part. pastInfinitive + gerund actionin progress

Regret & criticism

You ought to have fed the cat and dog.

It’s my fault. I should have told you earlier my mother was coming.

Should and ought to

▪ Should have + past participle is used to criticise someone’s

actions or lack of them in the past, or in other words to say that

somebody didn’t do the right thing in the past.

Ought to have + past participle is used as

an alternative to should

Now it’s your turn!

Go to page 156 to complete exercise 3.

modal verbs for speculation and deduction

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