Grammar. 25.10.2016
Grammar Teacher

Modals of deduction: Past & Present

Автор: Grammar Teacher

Deduction is the process of reaching a decision or answer by thinking about the known fact, or the decision that is reached. Well-known Sherlock Holmes used this method to find out the criminals.

Some of us use this method in everyday life for making conclusion in our native language. We use deduction in English as well. There is a list of modal verbs that are called 'modals of deduction' and they are going to be discussed in this article.

PRESENT. We use modals of deduction to say how sure we are about something. In present modals of deduction are: must, might, may, could, can't.

  • We use must when we feel sure that something is true because there’s very strong evidence:

He must live near here because he comes to work  on  foot. (We don’t know where he lives but we’re sure it’s not far away)
You are a computer programmer? It must be well-paid job.

  • We use might, may or could to say that we think something is possible but we’re not sure:

What do you know about him? He might be a reserved person.
They may be late on meeting.
Don't eat it! It could be poisoned!

  • We use can't/couldn't  when we assume that something is not true:

She can't be a mother, she's only 14!
He can't be in prison, I saw him yesterday in a pub.
They couldn't be in a library. It's closed today.

All modals of deduction in present depend on how certain you are about the fact.

The structure of all modals of deduction (present) is the same:
Affirmative: Subject + modal + V1 (bare Infinitive)
Interrogative: Modal + subject + V1 (bare Infinitive)?
Negative: No + subject + modal + not + V1 (bare Infinitive)

PAST. The structure of modals in the past is different, but the meaning is quite similar (just refers to the past):

  • Must  +  have Ved/3 - we are sure that something happened in the past:

Where is my wallet?! Someone must have stolen it!
You're soaked. It must have been raining outside.

  • Might, may, could + have Ved/3 - we think something was possible but we aren’t sure:

The thieves might have escaped by car but we can’t be sure.
He should be hour by now. He may have been delayed by a traffic jam or something.
I can’t find my purse. I could have left it in the supermarket but I just don’t know.

  • Can't, couldn't + have Ved/3 - we feel sure that something didn’t happen in the past:

I thought I saw John in town this morning but it can’t have been him – he’s in Greece this week.
I can’t have left it in the supermarket – I had it on the bus on the way home.
You can’t have read the instructions properly. They’re perfectly clear.

 

As you can see in examples above the structure of modals of deduction (past) is the following:
Affirmative: Subject + modal + have V3/ed 
Interrogative: Modal + subject + have V3/ed ?
Negative: No + subject + modal + not + have V3/ed

Here is a very good table from our Visual Grammar rubric of modals of deduction for you:

More examples and exercises for practice you can find here:

It must be thought-provoking!

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