ESL Inventory

Modals of Deduction and Probability: Examples & Exercises

Modals of Deduction and Probability, or Speculation, so many names for the same set of modals. And they can be Present, Past, and Future too, try this quiz and test yourself:

EXERCISE: Modals of Deduction / Probability (Round 1)

Choose the correct option to fill the gap.

1 / 10

That message _____ from Tom. He was offline all day.

2 / 10

You _____ be serious! This idea is too wild.

3 / 10

You _____ wrong, I never said that.

4 / 10

He _____ at home, the lights are on.

5 / 10

They _____ already, the house is empty.

6 / 10

They _____ be tired after that long trip.

7 / 10

We _____ the last bus, there’s no one at the stop.

8 / 10

He _____  the meeting — he didn’t show up.

9 / 10

She _____ be hungry, she’s just eaten a full meal.

10 / 10

This _____ be the right house, the number matches and the street name too.

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Was this too hard? Study the article below and try again.

We use these modals to guess, infer, or speculate about a situation. These are called modals of Deduction, Modals of Speculation or Modals of Probability. We choose different modals depending on how certain we are, and whether we’re talking about the present, past, or future.

The modal verbs ‘can’ and ‘could’ are also used as Modals of Prohibition and Permission,

Present Deduction

Used to say how likely something is right now.

ModalDegree of CertaintyUseExample
mustStrong certaintySure something is trueShe must be tired.
may / might / couldPossibilityMaybe trueHe might be at school.
can’t / couldn’tStrong impossibilitySure something is not trueThat can’t be the answer!

Structure:
Subject + modal + base verb

Infographic on Modals of Deduction

Infographic illustrating English Modals of deduction and probability with percentage-like circles: must, could, may, might, can't, couldn't. Designed for ESL learners, showing examples of modals of probability. Includes ESL Inventory owl logo and website link esl-inventory.com.
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Exercises on Present Deduction / Probability:

AutoEnglish | EnglishPage | PerfectEnglish1 | PerfectEnglish2 | TestEnglish |  LiveWorksheets1 | LiveWorksheets2 | OxfordUP | EnglishExercises | EslLounge | Grammaring | ELTbase

Past Deduction

Used to say how likely something was in the past.

ModalDegree of CertaintyUseExample
must haveStrong certaintySure it happenedShe must have left already.
may / might / could havePossibilityMaybe happenedHe might have forgotten the keys.
can’t / couldn’t haveStrong impossibilitySure it didn’t happenThey can’t have seen the message.

Structure:
Subject + modal + have + past participle

Exercises on Past Deduction and Probability:

Britishcouncil | Test-English |

Future Deduction

Used to talk about what is likely to happen or is unlikely to happen in the future, especially when imagining actions in progress or being planned.

Modal StructureDegree of CertaintyUseExample
must + be + -ingStrong certaintySure something is happening soonShe must be taking the train very early, her meeting is at 9am tomorrow.
should + be
(+ -ing)		ExpectationExpect something to happen soonShe should be arriving soon.
may / might / could + be + -ingPossibilitySomething might happen (action in progress)She might be going to the party tonight.
can’t / cannot + be + -ingStrong impossibilitySure something will not be happeningHe can’t be meeting us at 5, he’s abroad.

Structure:
Subject + modal + be + verb-ing

Please note that we can also use ‘will’ to speak about strong certainty in the future, please check Future Simple, Future Continuous (will be), and Future Perfect (will have) for reference.

Degrees of Certainty on modals of deduction

CertaintyModals
âś… Strong certaintymust (present/past), must have
🤔 Possibilitymay, might, could (all tenses)
❌ Strong impossibilitycan’t, couldn’t, can’t have

Exercises on Modals of Deduction and Probability

EXERCISE: Modals of Deduction / Probability (Round 2)

Choose the correct option to fill the gap.

1 / 10

I’m not sure, but she _____ us for lunch.

2 / 10

He _____ to Brazil next month like planned, his visa just got approved.

3 / 10

That dog _____ friendly, it’s wagging its tail.

4 / 10

They _____ soon, their car is still broken.

5 / 10

He _____ late tonight, he’s behind schedule.

6 / 10

She _____ to the dentist later, she has a toothache.

7 / 10

They_____ the new neighbors, they’re unloading all the furniture.

8 / 10

He _____ the game when we arrive.

9 / 10

They _____ the concert tomorrow, they bought tickets last week.

10 / 10

She _____ at work right now, her phone is off and she’s not allowed to use it at work.

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EXERCISE: Write a complete sentence with Modals of Deduction

Write complete sentences with Modals of Deduction. Use the words in bold as indicated.
Example:
Prompt: she – play the piano – all day (strong impossibility – past)
Answer: She can’t have played the piano all day.

1 / 10

It – be – a good idea (possibility – present)

2 / 10

It – be – true (strong impossibility – present)

3 / 10

He – be – the manager (strong certainty – present)

4 / 10

This – be – her phone (possibility – present)

5 / 10

They – know – the answer (strong impossibility – past)

6 / 10

She – be – serious (strong impossibility – present)

7 / 10

She – be – at home now (strong certainty – present)

8 / 10

He – be – tired (possibility – past)

9 / 10

You – be – right (possibility – past)

10 / 10

They – have – a lot of work to do (strong certainty – past)

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All these modals can have other meanings depending on the context, to learn more you can also study:

Modals of Ability
Modals of Advice
Obligation and Necessity
Permission and Prohibition