Modality B1 B2

Modal deduction and speculation

Judge present and future certainty with must, can't, may, might, could, and should.

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Visuaalinen opas

Modal deduction: the certainty scale

Evidence → choose the helper by certainty

IMPOSSIBLE       POSSIBLE          EXPECTED       ALMOST CERTAIN
can't            may / might /     should         must
                 could
   │                │                │              │
That can't be our taxi; the number is different.
They might be in the café.
The train should arrive soon.
The lights are on, so Ben must be home.

Shape:
person/thing + certainty helper + be / plain verb

✓ She must be tired.   ✗ She must tired.

Choose the modal by how sure the evidence makes you, then use it before be or the plain verb.

Introduction

Judging from evidence

Modal deduction and speculation help you judge what is true when you do not know for sure. You look at evidence, the situation, or normal expectations, then choose a modal to show your certainty. The lights are on, so Ben must be home. That can't be our taxi; the number is different. These sentences do not report direct facts; they report the speaker's present judgement about a present situation or a likely future result.

Core Kielioppi B1 Sanasto A2 Neutral

The lights are on, so Ben must be home.

Must shows a strong logical conclusion, not obligation, because the evidence points to it.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

The lights are on, so

evidence_frame

Gives the reason for the conclusion.

Ben must be home

strong_deduction

Shows a strong present conclusion from evidence.

Opettele yhtenä kokonaisuutena

Negative Kielioppi B1 Sanasto A2 Neutral

That can't be our taxi; the number is different.

Can't expresses a negative deduction: the speaker is sure something is not true.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

That can't be our taxi

impossible_deduction

Shows that the speaker thinks this possibility is impossible.

Opettele yhtenä kokonaisuutena

the number is different

evidence_frame

Gives the evidence for rejecting the idea.

Cognitive metaphor

A scale of certainty

Think of these modals as points on a certainty scale. Must is very strong: the evidence points clearly to one conclusion. Should means expected or likely because it is normal, planned, or reasonable. May, might, and could are in the middle: possible, but not claimed as certain. Can't is very strong in the opposite direction: the speaker thinks the idea is impossible. She must be the new manager. The train should arrive soon. This can't be the right key. They might be in the café.

Core Kielioppi B1 Sanasto A2 Neutral

She must be the new manager.

Must be is the normal frame for a strong conclusion about identity or state.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

She must be the new manager

strong_deduction

A strong conclusion about who she is.

Opettele yhtenä kokonaisuutena

Core Kielioppi B1 Sanasto A2 Neutral

The train should arrive soon.

Should often means the speaker expects something because it is normal, planned, or likely.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

The train should arrive soon

expected_result

Shows an expected result, but not complete certainty.

Opettele yhtenä kokonaisuutena

Negative Kielioppi B1 Sanasto A2 Neutral

This can't be the right key.

Can't is the opposite of must for deduction: the speaker feels sure the idea is wrong.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

This can't be the right key

impossible_deduction

Rejects the possibility as logically impossible or very unlikely.

Opettele yhtenä kokonaisuutena

Core Kielioppi B1 Sanasto A2 Neutral

They might be in the café.

Might be is useful when the speaker has a real possibility but weak evidence.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

They might be in the café

weak_possibility

Shows a possible present location without strong certainty.

Opettele yhtenä kokonaisuutena

Core pattern

The basic pattern

The core form is subject + modal + base verb. The modal does not add -s, -ed, or -ing, and the following verb stays in its base form. With adjectives, nouns, and places, use be after the modal. She must tired is a common mistake; She must be tired is correct. For future actions, use the same modal + base verb pattern: They may arrive early. For possible results, could is very common in speech: This could work.

Mistake Kielioppi B1 Sanasto A1 Neutral

She must tired.

After a modal, English needs the base verb. With an adjective like tired, use be.

Corrected Kielioppi B1 Sanasto A1 Neutral

She must be tired.

Use modal + be + adjective for deductions about states.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

She must be tired

strong_deduction

A reusable frame for a strong conclusion about someone's state.

Opettele yhtenä kokonaisuutena

Core Kielioppi B1 Sanasto A2 Neutral

They may arrive early.

May + base verb can speculate about a future action.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

They may arrive early

future_possibility

Shows a possible future event.

Opettele yhtenä kokonaisuutena

Spoken Kielioppi B1 Sanasto A2 Neutral

This could work.

Could often sounds natural for suggesting that something is possible.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

This could work

possible_result

A short reusable frame for a possible solution or result.

Opettele yhtenä kokonaisuutena

Form variations

Useful form variations

Deduction often uses be because we are judging a state, identity, place, or situation. Use modal + be + adjective, noun, or place for states and identities. Use modal + be + -ing for an action possibly happening now. Use modal + be + past participle for passive meanings. It might be raining downtown. The road may be closed. The report should be ready by noon. These patterns let you speculate about now, soon, or a future result without changing the modal form.

Core Kielioppi B2 Sanasto A2 Neutral

It might be raining downtown.

Use modal + be + -ing for speculation about an action in progress.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

It might be raining

continuous_speculation

Shows a possible action happening now.

Opettele yhtenä kokonaisuutena

downtown

place_context

Adds the place where the situation may be happening.

Core Kielioppi B2 Sanasto A2 Neutral

The road may be closed.

Use modal + be + past participle when the subject receives an action or is in a passive state.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

The road may be closed

passive_speculation

Shows a possible passive state.

Opettele yhtenä kokonaisuutena

Formal Kielioppi B1 Sanasto A2 Formal

The report should be ready by noon.

Should be ready is common for expected completion, especially in work or service contexts.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

The report should be ready

expected_ready_state

Shows an expected state.

Opettele yhtenä kokonaisuutena

by noon

deadline

Gives the expected time limit.

Usage rules

Negatives and questions

Negative forms do not all mean the same thing. May not and might not mean that a negative situation is possible: the speaker is not sure. Can't means the speaker is sure the idea is not true. She may not know the address. He can't be asleep; his light is on. In questions, could is the most common neutral choice for asking about a possible explanation. Could this be a mistake? Might they need more time? Might sounds more careful or formal than could.

Negative Kielioppi B1 Sanasto A2 Neutral

She may not know the address.

May not means possible non-truth, not impossibility.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

She may not know

negative_possibility

Shows that it is possible she does not know.

Opettele yhtenä kokonaisuutena

the address

object

Says what she may not know.

Negative Kielioppi B1 Sanasto A2 Neutral

He can't be asleep; his light is on.

Can't is much stronger than may not or might not.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

He can't be asleep

impossible_deduction

Shows the speaker is sure the idea is false.

Opettele yhtenä kokonaisuutena

his light is on

evidence_frame

Gives the evidence for the deduction.

Question Kielioppi B1 Sanasto A2 Neutral

Could this be a mistake?

Could is common and natural in questions about possible explanations.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

Could this be a mistake

possibility_question

Asks whether something is possible.

Opettele yhtenä kokonaisuutena

Question Kielioppi B2 Sanasto A2 Formal

Might they need more time?

Might can form speculation questions, especially when the speaker is cautious.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

Might they need more time

possibility_question

Asks about a possible need, often a little more careful or formal than could.

Opettele yhtenä kokonaisuutena

Contrast

Deduction is not obligation

The closest confusion is must for deduction versus must for obligation. You must be cold means I conclude this from what I see or know. You must wear a coat means I am giving a rule or strong instruction. The verb pattern and situation decide the meaning. Another important contrast is can't versus mustn't. Can't can reject a possibility in deduction. Mustn't means prohibition, so it is usually a rule or warning, not a logical conclusion.

Contrast Kielioppi B1 Sanasto A1 Neutral

You must be cold.

Here must is deduction because it is followed by be + adjective and fits the evidence.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

You must be cold

deduction_not_obligation

Shows a conclusion about someone's state, not a command.

Opettele yhtenä kokonaisuutena

Contrast Kielioppi B1 Sanasto A1 Neutral

You must wear a coat.

Must can also express obligation; context and verb meaning decide the reading.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

You must wear a coat

obligation

Shows a rule or command, not a deduction.

Opettele yhtenä kokonaisuutena

Danger zone

Common boundaries

Do not use can for a single uncertain future guess in ordinary English. It can rain in April means rain is generally possible in April. For one specific future situation, use may, might, or could: It might rain tonight. Also remember that these modals normally describe present or future judgement in this lesson. For past deduction, English uses forms such as must have left or might have forgotten; those are a separate pattern and should not be mixed with the simple present/future frames here.

Exception Kielioppi B1 Sanasto A1 Neutral

It can rain in April.

Can is natural for general possibility, but not usually for a single uncertain future event.

Rakennuspalikat

Lue lause merkityskokonaisuuksina, älä sana sanalta.

It can rain

general_possibility

Shows something that is generally possible, not a one-time guess.

Opettele yhtenä kokonaisuutena

in April

general_time_context

Marks the sentence as a general statement about a season or period.

Summary

The practical choice

Choose the modal by asking how strong your evidence is. Use must when the evidence strongly points to yes. Use can't when the evidence strongly points to no. Use may, might, or could when something is only possible. Use should when something is expected because it is normal, planned, or likely. Keep the form simple: modal + base verb, modal + be + adjective/place/noun, modal + be + -ing, or modal + be + past participle. The modal shows your judgement, not a guaranteed fact.

Oppiminen

Työkalut

Tutustu

Yritys & Tuki

Modal deduction and speculation

Modal deduction: the certainty scale

Judging from evidence

Rakennuspalikat

Rakennuspalikat

A scale of certainty

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

The basic pattern

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

Useful form variations

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

Negatives and questions

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

Rakennuspalikat

Deduction is not obligation

Rakennuspalikat

Rakennuspalikat

Common boundaries

Rakennuspalikat

The practical choice

Oppiminen

Työkalut

Resurssit

Yritys

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