Grammar Rule in 30 Seconds
Use 'can't' to say you are 100% sure something is impossible based on the evidence you see.
- Use 'can't + base verb' for present impossibility: 'He can't be home.'
- Use 'can't have + past participle' for past impossibility: 'She can't have left.'
- Never use 'mustn't' for logical impossibility; 'mustn't' is for prohibition only.
Overview
can't와 couldn't have가 바로 이 역할을 합니다. 이 문법을 제대로 익히면 단순히 사실을 전달하는 수준을 넘어, 자신의 확신과 논리적인 판단을 원어민처럼 자연스럽고 힘 있게 전달할 수 있게 됩니다.No라고 하기보다, That can't be true. He is in Europe now!라고 말하며 논리적인 근거를 바탕으로 불가능함을 표현할 수 있습니다.can의 부정형을 사용하는 것입니다. 흔히 can't를 «할 수 없다»는 능력의 부정으로만 알고 계신 경우가 많은데, 추측이나 판단의 영역으로 넘어오면 «~일 리가 없다»라는 강한 부정적 확신을 의미하게 됩니다.must와의 관계입니다. 우리가 어떤 사실이 분명하다고 확신할 때(Positive Deduction) must(«~임에 틀림없다»)를 사용하죠? 그 반대 지점, 즉 «절대 아님이 틀림없다»라고 말하고 싶을 때 사용하는 조동사가 바로 can't입니다.can't- 예:
The store can't be closed; it's only 2 PM.(가게가 문을 닫았을 리가 없어요. 지금 겨우 오후 2시거든요.)
couldn't havecan't have도 사용 가능하지만, 과거의 일을 추론할 때는 couldn't have가 훨씬 더 자연스럽고 빈번하게 사용된다는 점입니다.- 예:
She couldn't have sent that email. Her computer was broken yesterday.(그녀가 그 이메일을 보냈을 리가 없어요. 어제 그녀의 컴퓨터가 고장 났었거든요.)
can't + Base Verb | It can't be true. (그럴 리가 없어.) |couldn't have + Past Participle (p.p.) | He couldn't have known. (그가 알았을 리가 없어.) |- 1현재 상태/사실에 대한 부정적 추측:
- 공식: 주어 +
can't+ 동사원형 You can't be hungry. You just had a big lunch.(배고플 리가 없잖아. 방금 점심 거하게 먹었으면서.)- 여기서
can't뒤에be동사가 자주 오는 이유는 상태에 대한 추측을 많이 하기 때문입니다.
- 1과거 사실에 대한 부정적 추측:
- 공식: 주어 +
couldn't have+ 과거분사(p.p.) They couldn't have arrived yet. The traffic is terrible.(그들이 벌써 도착했을 리가 없어. 교통 체증이 엄청나거든.)- 많은 한국인 학습자들이
couldn't뒤에 바로 과거형 동사를 쓰는 실수를 합니다. 반드시have + p.p.형태를 지켜주세요.
- 1부정의 강도 조절:
cannot(축약하지 않은 형태)을 쓰면 훨씬 더 격식 있고 단호한 느낌을 줍니다.It cannot be possible.(그것은 도저히 가능할 수 없습니다.)
- 상황: 친구가 한 달 만에 토익 만점을 받았다고 합니다.
- 표현:
You can't be serious! You didn't even study last week.(진심 아니지? 너 지난주에 공부도 안 했잖아.)
- 상황: 배달 앱에서 음식이 배달 완료되었다고 떴는데, 문 앞에는 아무것도 없습니다.
- 표현:
The food couldn't have been delivered. I've been waiting right by the door.(음식이 배달되었을 리가 없어요. 제가 계속 문 바로 옆에서 기다리고 있었거든요.)
- 상황: 누군가 어제 밤 10시에 PC방에서 나를 봤다고 주장합니다. 하지만 나는 그때 집에서 자고 있었습니다.
- 표현:
You couldn't have seen me at the PC bang. I was fast asleep at home then.(네가 나를 PC방에서 봤을 리가 없어. 난 그때 집에서 곯아떨어져 있었거든.)
- 상황: 낮인데 별이 보인다는 아이에게 설명할 때.
- 표현:
You can't see stars now. The sun is too bright.(지금은 별을 볼 수 없어(볼 수 있을 리가 없어). 태양이 너무 밝거든.)
can't 대신 mustn't을 사용하는 실수must니까, «~ 아님이 틀림없다»를 must not이라고 생각하기 쉽습니다. 하지만 영어에서 mustn't은 금지(Prohibition)의 의미일 뿐, 논리적 추측에는 쓰이지 않습니다.He mustn't be at home. | He can't be at home. | mustn't은 «집에 있으면 안 된다(금지)»는 뜻이 됩니다. |It mustn't be true. | It can't be true. | «사실일 리가 없다»는 논리적 판단은 반드시 can't를 씁니다. |couldn't have 뒤에 동사 과거형을 쓰는 실수couldn't have went 처럼 쓰는 경우가 많습니다. 조동사 뒤에 완료형(have p.p.)이 올 때는 반드시 과거분사를 써야 합니다.- ❌
They couldn't have saw us. - ✅
They couldn't have seen us.(그들이 우리를 봤을 리가 없어.)
I can't swim.은 «수영을 할 줄 모른다(능력)»는 뜻입니다. 하지만 It can't be 5 o'clock.은 «5시일 리가 없다(판단)»는 뜻이죠. 문맥에 따라 can't가 '능력'인지 '추측'인지 구분하는 연습이 필요합니다. 보통 주어가 사람이 아니고 사물이나 상황(It, That 등)일 때는 '추측'일 확률이 매우 높습니다.can't vs may/might notcan't는 근거가 확실할 때 쓰는 말입니다. 반면 might not은 그냥 «아닐 수도 있지 뭐» 정도의 약한 추측입니다.He can't be Korean.(그는 한국인일 리가 없어. - 여권을 봤거나 말을 전혀 못 하는 등 확실한 근거가 있음)He might not be Korean.(그는 한국인이 아닐지도 몰라. - 그냥 외모만 보고 추측함)
couldn't vs couldn't have p.p.couldn't는 단순히 과거에 «할 수 없었다(능력)»를 의미할 때가 많고, couldn't have p.p.는 과거의 특정 시점에 그 일이 «일어났을 리가 없다(추측)»는 의미로 고정됩니다.I couldn't go.(나는 갈 수 없었다. - 능력/상황)I couldn't have gone.(내가 갔을 리가 없다. - 추측/부정)
can't 대신 couldn't를 현재 추측에 써도 되나요?That couldn't be true.라고 하면 can't보다 약간 더 조심스럽거나 가정적인 느낌(«그럴 리가 없을 텐데요»)을 주지만, 실질적으로 강한 부정적 추측을 나타내는 것은 동일합니다.can't have p.p.는 안 쓰나요?can't have p.p.를 꽤 자주 쓰는 편입니다. 하지만 미국 영어와 일반적인 회화에서는 과거의 논리적 추측에 couldn't have p.p.를 더 선호하는 경향이 있습니다. 둘 다 의미 차이는 거의 없으니 편한 것을 선택하셔도 됩니다.can't be와 don't be는 어떻게 다른가요?Don't be silly.는 «바보같이 굴지 마»라는 명령/충고입니다. 반면 You can't be silly.는 «네가 바보 같을 리가 없어(너는 똑똑한 사람이니까)»라는 논리적 판단입니다. can't는 언제나 '판단'의 영역이라는 점을 기억하세요!Can it be true?라고 물으면 «그게 정말 사실일 수 있을까? (설마 그럴 리가?)»라는 의구심 섞인 질문이 됩니다. 대답할 때 No, it can't be.라고 하면 완벽한 대화가 되겠죠?can't와 couldn't have p.p.! 이제 여러분도 상대방의 말에 논리적으로 반박하거나, 자신의 확신을 멋지게 표현할 준비가 되셨나요? «그럴 리가 없어!»라는 생각이 들 때, 주저 말고 이 패턴을 꺼내 보세요. 훨씬 더 스마트하고 논리적인 영어 구사자가 될 것입니다. 쉽죠? 이렇게 하나씩 원리를 이해하면 영어 문법은 더 이상 암기 대상이 아니라 즐거운 논리 게임이 됩니다. 수고하셨습니다!Forming Logical Impossibility
| Tense | Subject | Modal | Auxiliary/Verb | Example |
|---|---|---|---|---|
|
Present
|
I/You/He/She/It/We/They
|
can't
|
be / do / go
|
It can't be true.
|
|
Present Continuous
|
I/You/He/She/It/We/They
|
can't
|
be + -ing
|
They can't be sleeping.
|
|
Past
|
I/You/He/She/It/We/They
|
can't
|
have + past participle
|
She can't have left.
|
|
Past Continuous
|
I/You/He/She/It/We/They
|
can't
|
have been + -ing
|
He can't have been driving.
|
Contractions
| Full Form | Contraction | Usage Note |
|---|---|---|
|
cannot
|
can't
|
Most common in speech and informal writing.
|
|
cannot have
|
can't have
|
Commonly used for past deductions.
|
|
could not
|
couldn't
|
Used for past ability or less certain deduction.
|
Meanings
The use of the modal verb 'can't' to express a firm belief that something is not true or impossible because the facts or situation suggest otherwise.
Present Impossibility
Expressing that a current state or action is impossible right now.
“You've just eaten a whole pizza; you can't be hungry!”
“That can't be the right answer; it doesn't make sense.”
Past Impossibility
Expressing that an event in the past was impossible.
“She can't have stolen the money; she was with me all day.”
“They can't have finished the project already; they only started an hour ago.”
Theoretical Impossibility
Used in scientific or mathematical contexts to state that something is fundamentally impossible.
“A triangle can't have four sides.”
“Nothing can't travel faster than the speed of light.”
Reference Table
| 주어 | 현재 불가능성 | 과거 불가능성 | 예시 (현재) | 예시 (과거) |
|---|---|---|---|---|
|
I
|
can't be
|
couldn't have been
|
I can't be late again.
|
I couldn't have been serious.
|
|
You
|
can't be
|
couldn't have been
|
You can't be hungry already!
|
You couldn't have finished already.
|
|
He/She/It
|
can't be
|
couldn't have been
|
He can't be home yet.
|
She couldn't have known.
|
|
We
|
can't be
|
couldn't have been
|
We can't be lost.
|
We couldn't have forgotten.
|
|
They
|
can't be
|
couldn't have been
|
They can't be right.
|
They couldn't have told us.
|
격식 수준 스펙트럼
It is highly improbable that such a statement is accurate. (Reacting to a rumor)
That can't be true. (Reacting to a rumor)
No way! That's impossible. (Reacting to a rumor)
Cap! (AAVE) / You're kidding, right? (Reacting to a rumor)
논리적 불가능성: 그럴 리 없어!
현재/미래
- Can't be It's impossible that it is
- Can't + verb Subject cannot perform action
과거
- Couldn't have been It's impossible that it was
- Couldn't have + past participle Subject could not have performed action
핵심 대비
- Must be Logical certainty (positive)
- Mustn't Prohibition (not impossibility)
Can't Be vs. May Not Be vs. Mustn't Be
논리적 불가능성 사용 결정하기
어떤 것이 사실이 아니라는 강력한 추론을 하고 있나요?
불가능성이 현재 또는 미래에 관한 것인가요?
불가능성이 과거에 관한 것인가요?
논리적 불가능성이 빛나는 순간
불신/놀라움
- • 터무니없는 소문을 들었을 때
- • 예상치 못한 결과를 보았을 때
- • 충격적인 소식에 반응할 때
모순되는 증거
- • 미스터리 속 알리바이
- • 진술 사실 확인
- • 잘못된 정보 수정
상식/논리
- • 나이 대 성과
- • 날씨 대 옷차림
- • 알려진 일정 대 주장
수준별 예문
He can't be 5 years old; he is very tall.
He can't be 5 years old; he is very tall.
It can't be raining; the sun is shining.
It can't be raining; the sun is shining.
You can't be hungry again!
You can't be hungry again!
That can't be my bag; mine is blue.
That can't be my bag; mine is blue.
She can't be at work; it's Sunday.
She can't be at work; it's Sunday.
They can't be tired; they slept for ten hours.
They can't be tired; they slept for ten hours.
This can't be the right road; we are lost.
This can't be the right road; we are lost.
He can't be the winner; he finished last.
He can't be the winner; he finished last.
You can't have seen her; she moved to Australia last year.
You can't have seen her; she moved to Australia last year.
He can't have finished the exam already; it's only been ten minutes.
He can't have finished the exam already; it's only been ten minutes.
They can't be living here; the house is completely empty.
They can't be living here; the house is completely empty.
It can't have been a ghost; ghosts don't exist.
It can't have been a ghost; ghosts don't exist.
The witness can't be telling the truth; her story keeps changing.
The witness can't be telling the truth; her story keeps changing.
You can't have been paying attention if you didn't hear the alarm.
You can't have been paying attention if you didn't hear the alarm.
The results can't have been faked; the lab is very reputable.
The results can't have been faked; the lab is very reputable.
He can't be serious about quitting his job now.
He can't be serious about quitting his job now.
The economy can't possibly recover as quickly as the government claims.
The economy can't possibly recover as quickly as the government claims.
Surely he can't have been so naive as to believe their promises.
Surely he can't have been so naive as to believe their promises.
The manuscript can't be an original; the ink is far too modern.
The manuscript can't be an original; the ink is far too modern.
You can't have failed to notice the tension in the room.
You can't have failed to notice the tension in the room.
One cannot but conclude that the hypothesis can't be sustained under such scrutiny.
One cannot but conclude that the hypothesis can't be sustained under such scrutiny.
The sheer scale of the project means it can't have been undertaken without significant capital.
The sheer scale of the project means it can't have been undertaken without significant capital.
It can't be overemphasized how critical this junction was in history.
It can't be overemphasized how critical this junction was in history.
He can't have been anything other than devastated by the news.
He can't have been anything other than devastated by the news.
혼동하기 쉬운
Learners think 'mustn't' is the negative of 'must' for logic, but it's only for rules.
In the past, both 'can't have' and 'couldn't have' are used for deduction.
Learners use 'can't' when they are only slightly unsure.
자주 하는 실수
He no can be here.
He can't be here.
It can't to be true.
It can't be true.
She can't is happy.
She can't be happy.
I can't be hungry.
I'm not hungry.
You mustn't be hungry.
You can't be hungry.
He can't be at home yesterday.
He can't have been at home yesterday.
That don't can be right.
That can't be right.
She can't had seen him.
She can't have seen him.
It can't be happened.
It can't have happened.
He can't be knowing the answer.
He can't know the answer.
It can't have been being done.
It can't have been done.
문장 패턴
It can't be ___ because ___.
You can't have ___ already!
He can't be ___ing right now.
There can't have been any ___.
Real World Usage
This photo can't be real; it looks photoshopped.
There can't have been a mistake in my application.
This can't be the right gate; the flight number is different.
This can't be my order; I'm a vegetarian and this is pepperoni.
He can't be serious! 😱
The data cannot be reconciled with the previous findings.
반대를 생각해 봐요!
'mustn't'는 절대 안 돼요!
'possibly'를 더해서 강조해 봐요!
'can't!'를 말할 때 억양이 중요해요!
Smart Tips
Immediately reach for 'can't be'. It's the most natural way to express this in English.
Use 'can't have' to sound more persuasive and analytical.
Use the phrase 'You can't be serious!' to show immediate disbelief.
Use 'cannot' instead of 'can't' and add 'possibly' for academic weight.
발음
The 't' in can't
In American English, the 't' is often a 'stop t', meaning the tongue stops the air but doesn't release it. In British English, the 'a' is long /kɑːnt/.
Contraction stress
We usually stress 'can't' more than 'can' to make the negative clear.
Rising-Falling for Disbelief
That can't be ↘ right!
Strong emphasis on the impossibility.
암기하기
기억법
C.A.N.T. stands for Certainty Against New Truths.
시각적 연상
Imagine a detective holding a magnifying glass over a clue that has a big red 'X' through it. The 'X' represents 'can't'.
Rhyme
If the facts say no, and you're sure it's so, use 'can't' to let the logic flow.
Story
A man sees his friend's car in the driveway, but the house is dark. He thinks, 'He must be home.' Then he sees his friend post a photo from Hawaii on Instagram. He realizes, 'He can't be home!' The Instagram post is the evidence that changes his deduction.
Word Web
챌린지
Look around your room. Find three things that 'can't' be true right now (e.g., 'My cat can't be a dog'). Say them out loud.
문화 노트
British speakers use 'can't' frequently in social situations to politely disagree. Instead of saying 'You are lying,' they might say 'That can't be right, surely?'
Americans often use 'No way' or 'Get out of here' as idiomatic substitutes for 'That can't be true' in casual conversation.
In scientific papers, 'cannot' is preferred over 'can't' to maintain a formal tone when dismissing theories.
The word 'can' comes from the Old English 'cunnan', meaning 'to know' or 'to know how to'.
대화 시작하기
Look at that person over there wearing a winter coat in summer. Why are they doing that?
I heard that our teacher is actually a secret agent. What do you think?
The store is closed, but the lights are on inside. Why?
My phone says it's 2050. Is it broken?
일기 주제
자주 하는 실수
Test Yourself
He's only 16, so he ___ a licensed driver yet.
Find and fix the mistake:
They mustn't be home. Their car isn't in the driveway.
Arrange the words in the correct order:
All words placed
Click words above to build the sentence
Score: /3
연습 문제
8 exercisesThe lights are off. He ___ be at home.
You ___ (see) him yesterday; he was in Paris.
Find and fix the mistake:
He mustn't be the thief because he has an alibi.
I am sure that isn't your car.
We use 'mustn't' when we are 100% sure something is not true.
A: I just saw a UFO! B: You ___ serious!
Select the correct sentence.
1. The car is gone. 2. He's only 10. 3. It's summer.
Score: /8
Practice Bank
12 exercisesShe said she was busy, so she ___ at the party last night.
The meeting mustn't start without the boss.
Choose the correct sentence:
Translate into English: 'Es imposible que él haya hecho eso.'
Arrange these words into a sentence:
Match the situations with the correct impossibility:
Judging by the size, this ring ___ real diamonds; it's too cheap.
My cat weren't able to open the fridge.
Which sentence is correct?
Translate into English: 'Das kann nicht wahr sein!'
Arrange these words into a sentence:
Given the traffic, they ___ arrived at the airport on time.
Score: /12
자주 묻는 질문 (8)
Yes, for past deductions like `couldn't have been`, they are very similar. In the present, `couldn't` sounds slightly less certain or more hypothetical than `can't`.
In English, `mustn't` specifically means 'it is forbidden'. If you say 'He mustn't be rich,' it sounds like you are telling him he is not allowed to be rich!
Yes, `cannot` is used in formal writing and for strong emphasis. In daily speech, `can't` is much more natural.
Use the formula: `can't + have + past participle`. For example: 'He can't have forgotten.'
No, it can also mean a lack of ability ('I can't swim') or lack of permission ('You can't go out'). Context tells you which one it is.
Absolutely. 'He can't be the doctor' is a very common way to express deduction about a person's identity or role.
If you have any doubt, use `might not` or `may not`. Only use `can't` when you are effectively 100% sure based on the evidence.
Rarely. We usually use 'Can...?' or 'Could...?' for questions. 'Can it be true?' is more common than 'Can't it be true?'
Scaffolded Practice
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In Other Languages
No puede ser
English distinguishes strictly between 'mustn't' (prohibition) and 'can't' (logic).
Ce ne peut pas être
French uses the passé composé of 'pouvoir', while English uses a modal perfect.
Das kann nicht sein
German 'muss nicht' means 'don't have to', which is a different modal category entirely.
~hazu ga nai (~はずがない)
Japanese uses a noun-based construction ('hazu' means expectation).
la yumkin an yakun (لا يمكن أن يكون)
Arabic uses a full clause structure rather than a simple modal verb.
bù kěnéng (不可能)
Chinese doesn't conjugate for tense, so 'can't be' and 'can't have been' look the same without time markers.
Learning Path
Prerequisites
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관련 동영상
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영어 문법 can't be, mustn't be, may not be 차이점 완벽 정리! (조동사)
라이브 아카데미
조동사 can't be, mustn't be, may not be, might not be 차이점
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