Modals of deduction: must, might, can't을(를) 공부할 때 가장 집중해야 할 부분은 무엇인가요?

Must expresses near certainty that something is true: the lights are on, somebody must be inside. Can't expresses near certainty that something is impossible: she can't be thirty, she looks eighteen. Might, may, and could express realistic possibility: take an umbrella, it might rain this afternoon.

B1grammar문제 17개

Modals of deduction: must, might, can't

규칙

Must, might, could, and can't express logical deductions about present situations based on observable evidence.

Modals of Present Deduction (Epistemic Present Modals) are used when a speaker makes a logical evaluation, judgment, or deduction about a current situation based on observable evidence or circumstances. Degrees of Epistemic Certainty: (1) MUST (95% Positive Certainty): Used when the speaker is virtually certain that something is true because the evidence points overwhelmingly to that conclusion: "The office lights are illuminated and his car is outside; David must be at work", "She has studied architecture for six years; she must be very knowledgeable". (2) CAN'T (95% Negative Certainty / Impossibility): Used when the speaker is virtually certain that something is impossible because the evidence completely contradicts it: "That man can't be sixty years old; he looks thirty", "She can't be at home right now; I just saw her walking into the supermarket". (3) MIGHT / MAY / COULD (30–50% Real Possibility): Used when the speaker deduces that something is possible, but lacks conclusive proof to be certain: "Why isn't the train here yet? — There might be a signal delay down the line", "Don't touch that wire; it could be dangerous", "Take an umbrella; it may rain this afternoon". Formula: Subject + must / can't / might / could + BARE BASE VERB ("He must be at home", "She can't know about it").

기억할 것

Must expresses near certainty that something is true: the lights are on, somebody must be inside.
Can't expresses near certainty that something is impossible: she can't be thirty, she looks eighteen.
Might, may, and could express realistic possibility: take an umbrella, it might rain this afternoon.

피해야 할 흔한 함정

Never use must not to express that something is impossible: say it can't be true, never it must not be true.

Guía visual

How to read this B1 topic

At B1, grammar links ideas: condition, result, reported meaning, experience, and narrative order.

1. Name the relationship

Ask whether the sentence gives a condition, contrast, cause, report, or result.

If it rains, we will stay home.

2. Separate time from aspect

Finished event, visible result, duration, and background action use different forms.

I had left before she arrived.

3. Test both clauses

In complex sentences, the second half often proves the first half.

I wish I knew.

Modal verbs

Modals are followed by the base verb. They do not take third-person -s.

Meaning	Present / future	Past or perfect reference	Example
ability	can	could / was able to	She can swim.
obligation	must / have to	had to	We must leave.
advice	should	should have + participle	You should rest.
deduction	must / might / can't	must have / might have / can't have	He must be tired.

Contrasts that often decide the answer

Event or background

Simple forms move events forward; continuous forms show an action in progress.

I left while she was talking.

Fact or stance

Modals, hedges, and reporting structures show how certain or responsible the speaker sounds.

This may indicate a problem.

Clause or compressed phrase

Advanced writing often compresses full clauses into participle, noun, or prepositional phrases.

Having reviewed the data, we revised the plan.

예문

1The office lights are on and his bicycle is parked outside; David must be inside.
2That luxury sports car can't belong to a high school student; it costs a fortune.
3Take your warm coat with you; it might turn very chilly later this evening.
4She speaks four languages with flawless accents; she must be an interpreter.
5The front door is locked and the blinds are drawn; they can't be having a party.
6Don't eat those wild forest mushrooms; they could be poisonous and dangerous.
7Why isn't the bus arriving? — There might be heavy road construction ahead.
8He has been jogging in the summer heat for two hours; he must be very thirsty.
9That answer can't be correct; two plus two definitely equals four.
10Sophia isn't answering her desk phone; she may be attending a client presentation.

예외

Can't vs. Must Not: To state that something is logically impossible, English obligatorily uses can't, NOT must not: say "He can't be French; he doesn't speak a word of it", never "He must not be French". Must not expresses prohibition (you are forbidden to do it), not logical deduction. Could vs. Couldn't: Could expresses possibility ("It could be true"), but couldn't expresses impossibility ("It couldn't be true" = it can't be true).

자주 하는 실수

(1) Using must not for impossibility: "She must not be at home; the house is dark." → "She can't be at home; the house is dark." (Impossibility takes can't). (2) Adding to after deduction modals: "He must to be tired." → "He must be tired." (Modals are followed by bare base verbs). (3) Confusing can with could/might: Using can for specific present deduction ("It can rain today" → "It might/could rain today").

실력 확인

Look at three mysterious situations around you and write deductions using must, might, and can't, then practise this topic.

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