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Vocabulary
ㄹ/을 수 없다

A2 phrase 9 min read

ㄹ/을 수 없다

-l/eul su eopda

Practice it Examples Notes & Tips ㄹ/을 수 없다 in 30 Seconds

Explanation ㄹ/을 수 없다 in your Level:

At the A1 level, learners are introduced to 'ㄹ/을 수 없다' as a basic formula to express that they cannot perform a specific action. The focus is on simple, everyday verbs like 'go' (가다), 'eat' (먹다), and 'meet' (만나다). At this stage, students learn the basic conjugation rule: use '-ㄹ 수 없다' if there is no bottom consonant and '-을 수 없다' if there is one. The context is usually immediate and physical, such as 'I can't go to school today' or 'I can't eat kimchi.' The goal is to distinguish this from simple negation ('not') and understand that it refers to capability or situational possibility. Learners should practice the polite '-어요' ending, resulting in '-(으)ㄹ 수 없어요.'

At the A2 level, the usage of 'ㄹ/을 수 없다' expands to include situational constraints and more varied verb types, including irregulars. Learners begin to use it to provide reasons for their inability, often pairing it with the '-아/어서' (because) structure. For example, '비가 와서 공원에 갈 수 없어요' (I can't go to the park because it's raining). This level also introduces the past tense '-(으)ㄹ 수 없었다' to describe things one was unable to do in the past. Students should become comfortable with 'ㄹ' irregulars (like '만들다' becoming '만들 수 없다') and 'ㄷ' irregulars (like '듣다' becoming '들을 수 없다'). The focus is on practical communication in daily life, such as making excuses or explaining limitations during travel or shopping.

At the B1 level, 'ㄹ/을 수 없다' is used for more abstract concepts and complex social interactions. Learners move beyond physical inability to express psychological or emotional impossibility, such as '그 사람을 잊을 수 없어요' (I can't forget that person). The structure is also used in more formal settings, such as '-(으)ㄹ 수 없습니다' in work-related emails or announcements. At this stage, students should start comparing 'ㄹ/을 수 없다' with alternatives like '-지 못하다' to understand the subtle difference between 'lack of possibility' and 'lack of ability/circumstance.' They also learn to use it with adverbs like '전혀' (at all) or '도저히' (not possibly) to add emphasis to their statements.

At the B2 level, learners explore idiomatic and advanced uses of 'ㄹ/을 수 없다.' This includes the double negative structure '-지 않을 수 없다,' which means 'cannot help but do' or 'have no choice but to do' (e.g., '웃지 않을 수 없었다' - I couldn't help but laugh). This level requires a high degree of accuracy in both spelling and nuance. Learners use the phrase in argumentative contexts to state why a certain conclusion cannot be reached or why a certain action is impossible under specific legal or social frameworks. The distinction between 'ㄹ 수 없다' and '-(으)ㄹ 리가 없다' (there is no way that...) becomes a focus, as students learn to express different degrees of certainty and logical impossibility.

At the C1 level, 'ㄹ/을 수 없다' is integrated into sophisticated discourse. It appears frequently in academic writing and formal speeches to define the limits of a theory or the impossibility of a certain outcome. Learners use it in complex sentence structures, often as part of a larger modifying clause (e.g., '회복할 수 없는 손상' - irreparable damage). The focus is on the precision of the phrase in technical or literary contexts. Students also learn how it interacts with honorifics and highly formal registers, such as '-(으)ㄹ 수 없으십니다' when referring to a person of high status who is unable to do something. They are expected to use the phrase naturally in nuanced debates, expressing subtle shades of impossibility.

At the C2 level, 'ㄹ/을 수 없다' is handled with native-like mastery, including its use in classical-style proverbs, complex legal jargon, and high-level literature. The speaker can use the phrase to convey irony, sarcasm, or deep philosophical impossibility. They understand the historical development of the '수' (possibility) noun and can recognize archaic or dialectal variations of the structure. At this level, the focus is on the perfect integration of the phrase within the flow of high-level rhetoric. The learner can effortlessly switch between 'ㄹ 수 없다' and its many synonyms (like '불가능하다', '여지가 없다', '방법이 없다') depending on the desired register and rhetorical effect, ensuring the most impactful communication possible.

Practice it Examples Notes & Tips

ㄹ/을 수 없다 in 30 Seconds

The Korean phrase for 'cannot' or 'unable to,' used for both physical ability and situational impossibility.
Formed by adding -ㄹ 수 없다 to vowel-ending verb stems and -을 수 없다 to consonant-ending stems.
More formal and objective than the short negation '못,' making it ideal for professional and written contexts.
Can be used in past tense as '-(으)ㄹ 수 없었다' and with adverbs like '전혀' for emphasis.

The Korean grammatical structure ㄹ/을 수 없다 is one of the most fundamental ways to express inability, impossibility, or the lack of potential. In English, we translate this primarily as 'cannot' or 'be unable to.' However, to truly master its usage, one must understand the literal composition of the phrase. It consists of the prospective modifier suffix -(으)ㄹ, the dependent noun 수 (meaning 'way,' 'method,' or 'possibility'), and the negative existential verb 없다 (meaning 'to not exist'). Therefore, when you say you 'cannot' do something using this pattern, you are literally saying that 'the way or possibility to do it does not exist.'

Literal Breakdown: 수 (Su): A bound noun representing the means, possibility, or circumstance to perform an action. It never stands alone and always requires a modifier.
Grammatical Function: It functions as a complex predicate that negates the potential of the preceding verb. Unlike the short negation '못' (mot), which often implies a lack of skill or an external obstacle, ㄹ/을 수 없다 is more versatile and can describe absolute impossibility or situational constraints.

저는 매운 음식을 먹을 수 없습니다.
I cannot eat spicy food (The possibility of me eating it does not exist).

Native speakers use this phrase in various contexts ranging from physical limitations to social restrictions. For example, if a road is blocked, you would use this to say you cannot pass. If you lack a specific skill, like playing the piano, you use this to state your inability. It is considered more formal and clear than using the prefix '못,' making it the preferred choice in writing, public announcements, and polite conversations. In a professional setting, saying '할 수 없습니다' sounds more definitive and objective than '못 해요,' which can sometimes sound like a personal excuse or a lack of effort.

지금은 바빠서 갈 수 없어요.
I'm busy now, so I can't go.

Furthermore, this structure is essential for expressing logical impossibility. When something simply cannot be true based on the facts, ㄹ 수 없다 is employed. In academic or legal Korean, it appears frequently to define the boundaries of what is permissible or possible under certain conditions. Understanding this phrase is a gateway to moving beyond simple 'yes/no' statements and into the realm of describing capabilities and constraints in a nuanced, adult manner.

Using ㄹ/을 수 없다 requires a basic understanding of Korean verb conjugation, specifically how to attach future/prospective modifiers to verb stems. The rule is determined by whether the verb stem ends in a vowel or a consonant (batchim). This consistency makes it one of the more predictable patterns in Korean grammar, though there are a few irregular verbs to keep in mind.

Rule 1: Stems Ending in a Vowel: If the verb stem ends in a vowel, attach -ㄹ 수 없다 directly to the stem.
Example: 가다 (to go) → 가 + ㄹ 수 없다 → 갈 수 없다.
Rule 2: Stems Ending in a Consonant: If the verb stem ends in a consonant (batchim), attach -을 수 없다 to facilitate pronunciation.
Example: 먹다 (to eat) → 먹 + 을 수 없다 → 먹을 수 없다.
Rule 3: Stems Ending in 'ㄹ': If the stem already ends in 'ㄹ', you do not add another 'ㄹ'. Simply add 수 없다.
Example: 만들다 (to make) → 만들 수 없다.

비밀을 말할 수 없어요.
I cannot tell (you) the secret. (말하다 + ㄹ 수 없다)

Tense is expressed by conjugating the final verb 없다. To say 'could not' in the past tense, you change 없다 to 없었다. For example, 'I could not sleep' becomes '잠을 잘 수 없었어요.' It is a common mistake for beginners to try and change the verb stem (like '잤을 수 없다'), but the potential modifier always stays in its prospective form; only the ending 없다 carries the tense.

혼자서는 이 짐을 들 수 없었습니다.
I could not lift this luggage by myself. (들다 + 수 없었다)

When using this in questions, you simply change the intonation or add the question particle. '갈 수 없어요?' means 'Can't you go?' This is frequently used when expressing surprise at someone's inability to do something. In very formal situations, such as a presentation or a news broadcast, you will see the form -(으)ㄹ 수 없습니다, whereas in daily conversation with friends, -(으)ㄹ 수 없어 is common. Mastering the conjugation of this phrase allows you to set clear boundaries and describe limitations accurately in any social setting.

In South Korea, you will encounter ㄹ/을 수 없다 everywhere from the bustling streets of Seoul to the quietest library. It is the standard way to communicate 'prohibited' or 'unavailable' in public spaces. If you are at a museum, you might see signs that say '사진을 찍을 수 없습니다' (Photos cannot be taken). In a restaurant that has run out of a specific ingredient, the waiter might politely inform you, '지금은 주문할 수 없습니다' (You cannot order this right now).

In Public Transportation: Subway announcements often use this phrase to explain delays or safety rules. '안전 문이 닫힐 때는 탈 수 없습니다' (You cannot board when the safety doors are closing).
In K-Dramas and Movies: Dramatic scenes often utilize this phrase to express emotional impossibility. A character might cry out, '너를 보낼 수 없어!' (I can't let you go!) or '이 사실을 믿을 수 없어' (I can't believe this fact).

“죄송하지만, 더 이상 기다릴 수 없습니다.”
“I'm sorry, but I can no longer wait.” (Common in formal business or tense social situations)

In the workplace, this phrase is essential for managing expectations. When a deadline is impossible to meet, a Korean employee would say '기한 내에 끝낼 수 없습니다' (It cannot be finished within the deadline). It sounds more professional and objective than saying '못 해요,' which might imply a personal failure. By using ㄹ 수 없다, the speaker is focusing on the objective reality of the situation.

여기서는 담배를 피울 수 없습니다.
You cannot smoke here. (Standard prohibition sign language)

Socially, you'll hear it when friends discuss their schedules. If someone asks you to go to a concert but you have an exam, you would say '시험 때문에 갈 수 없어.' It's also found in song lyrics, frequently expressing the pain of an impossible love or the inability to forget a past lover. Because it covers both physical and metaphorical impossibility, it is one of the most high-frequency patterns you will encounter in any immersive Korean environment.

While ㄹ/을 수 없다 is straightforward, English speakers often stumble on its distinction from other negative forms and its specific conjugation rules. The most frequent error involves confusing it with the short negation '못' or the long negation '-지 못하다.' While they all translate to 'cannot,' the nuance and grammatical constraints differ significantly.

Mistake 1: Confusing with '못': '못' often implies a lack of ability or an external hindrance in a more casual, subjective way. ㄹ 수 없다 is more formal and describes objective impossibility. Using '못' in a formal report where ㄹ 수 없다 is expected can make the writing seem unprofessional.
Mistake 2: Doubling the 'ㄹ': Beginners often try to add an extra 'ㄹ' to verbs that already end in 'ㄹ'. For '살다' (to live), the correct form is 살 수 없다, not 살을 수 없다 or 살ㄹ 수 없다.
Mistake 3: Tense Placement: As mentioned before, learners frequently try to put the past tense on the main verb. Remember: It is 먹을 수 없었어요 (could not eat), NEVER 먹었을 수 없어요.

Incorrect: 수영할 수 못해요.
Correct: 수영할 수 없어요. / 수영을 못 해요.

Another common pitfall is using ㄹ 수 없다 with adjectives. In Korean, adjectives (descriptive verbs) generally do not use this potential form because 'possibility' is an action-oriented concept. You cannot say 'the weather cannot be cold' using '추울 수 없다' in the same way you say 'I cannot go.' Instead, you would use '-지 않다' or other structures like '-을 리가 없다' (there is no reason that...).

한국어를 전혀 할 수 없습니다.
I cannot speak Korean at all. (Note: Using '전혀' with this pattern emphasizes total inability.)

Finally, watch out for the spacing. In standard Korean orthography, there must be a space between the modifier (ㄹ/을) and the noun (수), and another space between the noun (수) and the verb (없다). Writing it as '할수없다' is a common spelling error even among native speakers in casual texting, but it is technically incorrect in formal writing.

To sound more natural and precise in Korean, it is important to know when to use ㄹ/을 수 없다 and when to choose an alternative. While it is the 'jack-of-all-trades' for 'cannot,' other structures offer specific shades of meaning that can make your speech more expressive.

-지 못하다: Comparison: Very similar to ㄹ 수 없다, but often implies that the speaker wants to do the action but is prevented by circumstances or lack of ability. ㄹ 수 없다 is more of a cold, hard statement of fact.
못 (Prefix): Comparison: The short form of '-지 못하다.' Used primarily in spoken, casual Korean. It is less formal than ㄹ 수 없다. You would use '못 가요' with friends but '갈 수 없습니다' in a speech.
-(으)ㄹ 리가 없다: Comparison: Translates to 'There is no way that...' or 'It's impossible that...' This is used for strong logical denial rather than physical inability. '그럴 리가 없어요' (That can't be true).

그는 거짓말을 할 리가 없어요.
There is no way he is lying. (Stronger than simply saying he 'cannot' lie)

Another useful alternative is -기(가) 힘들다 or -기(가) 어렵다. These literally mean 'it is difficult to...' but are often used as polite euphemisms for 'cannot.' If a Korean person says '지금은 도와드리기가 어렵습니다' (It is difficult to help you right now), they usually mean they cannot help you. It sounds much softer and less confrontational than '도울 수 없습니다.'

이 문제는 풀기 어려워요.
This problem is hard to solve. (Often used when 'cannot solve' sounds too definitive)

Lastly, for physical capability, the verb 못하다 can stand alone to mean 'to be bad at' something. While '노래를 할 수 없다' means you literally cannot sing (perhaps because of a sore throat), '노래를 못하다' means you are a bad singer. Knowing these distinctions prevents confusion and ensures you are conveying your intended meaning precisely.

How Formal Is It?

Fun Fact

In Middle Korean, '수' was used more broadly as a standalone noun, but in Modern Korean, it has become a 'bound noun' (의존 명사), meaning it can only exist when modified by a preceding word.

Pronunciation Guide

UK /r(u)l su ʌp̚.t͈a/

US /r(u)l su ʌp̚.t͈a/

Stress is usually equal across syllables, but the 'Su' can be slightly elongated for emphasis.

Rhymes With

할 수 없다 (Hal-su-eop-da) 갈 수 없다 (Gal-su-eop-da) 볼 수 없다 (Bol-su-eop-da) 살 수 없다 (Sal-su-eop-da) 알 수 없다 (Al-su-eop-da) 올 수 없다 (Ol-su-eop-da) 줄 수 없다 (Jul-su-eop-da) 쓸 수 없다 (Sseul-su-eop-da)

Common Errors

Pronouncing '없다' as 'eops-da' (the 's' should be silent before the 'd').
Making the 'ㄹ' too heavy like an American 'r'.
Forgetting to tense the 'd' in 'da' to a 't' sound (eop-ta).
Not spacing correctly between 'ㄹ' and 'su'.
Merging 'su' and 'eop' into one syllable.

Difficulty Rating

Reading 2/5

Easy to recognize due to the distinct '수 없다' ending.

Writing 3/5

Requires correct spacing and knowledge of batchim rules.

Speaking 3/5

Requires smooth transition between the verb and the 'ㄹ' sound.

Listening 2/5

Very common, so it becomes easy to hear with practice.

What to Learn Next

Prerequisites

없다 있다 가다 먹다 하다

Learn Next

ㄹ 수 있다 ㄹ 줄 알다/모르다 -지 못하다 ㄹ 리가 없다

Advanced

-지 않을 수 없다 -(으)ㄹ 수밖에 없다 -(으)ㄹ 여지가 없다

Grammar to Know

-(으)ㄹ 수 있다

한국어를 할 수 있어요. (I can speak Korean.)

-지 못하다

어제 잠을 자지 못했어요. (I couldn't sleep yesterday.)

-(으)ㄹ 수밖에 없다

공부할 수밖에 없어요. (I have no choice but to study.)

-(으)ㄹ 줄 알다/모르다

수영할 줄 몰라요. (I don't know how to swim.)

-기 어렵다/힘들다

가기가 힘들어요. (It's hard/impossible to go.)

Examples by Level

오늘 학교에 갈 수 없어요.

I cannot go to school today.

가다 + ㄹ 수 없어요

저는 김치를 먹을 수 없어요.

I cannot eat kimchi.

먹다 + 을 수 없어요

지금 친구를 만날 수 없어요.

I cannot meet my friend now.

만나다 + ㄹ 수 없어요

우유를 마실 수 없어요.

I cannot drink milk.

마시다 + ㄹ 수 없어요

영어를 할 수 없어요.

I cannot speak English.

하다 + ㄹ 수 없어요

이 책을 읽을 수 없어요.

I cannot read this book.

읽다 + 을 수 없어요

노래를 부를 수 없어요.

I cannot sing songs.

부르다 + ㄹ 수 없어요

운전을 할 수 없어요.

I cannot drive.

운전하다 + ㄹ 수 없어요

비가 와서 축구를 할 수 없어요.

I can't play soccer because it's raining.

Action impossible due to external reason (rain).

돈이 없어서 옷을 살 수 없어요.

I can't buy clothes because I have no money.

살다 (to buy) + ㄹ 수 없어요.

너무 매워서 먹을 수 없었어요.

It was too spicy, so I couldn't eat it.

Past tense: 없었다.

바빠서 전화를 받을 수 없었습니다.

I was busy, so I could not answer the phone.

Formal past tense: 없었습니다.

길이 막혀서 제시간에 올 수 없어요.

The road is blocked, so I can't come on time.

오다 + ㄹ 수 없어요.

다리가 아파서 걸을 수 없어요.

My legs hurt, so I can't walk.

걷다 (irregular) -> 걸을 수 없어요.

안경이 없어서 볼 수 없어요.

I don't have my glasses, so I can't see.

보다 + ㄹ 수 없어요.

비밀이라서 말할 수 없어요.

It's a secret, so I can't tell you.

말하다 + ㄹ 수 없어요.

도저히 그 사실을 믿을 수 없어요.

I simply cannot believe that fact.

Using '도저히' for emphasis.

전혀 이해할 수 없는 행동이에요.

It is behavior that I cannot understand at all.

Using '전혀' for total negation.

더 이상 기다릴 수 없습니다.

I can no longer wait.

Formal register for setting boundaries.

그의 목소리를 잊을 수 없어요.

I cannot forget his voice.

Abstract/Emotional inability.

혼자서는 이 문제를 해결할 수 없어요.

I cannot solve this problem alone.

Situational limitation.

예약 없이는 입장할 수 없습니다.

You cannot enter without a reservation.

Conditional impossibility.

이 약 없이는 잠을 잘 수 없어요.

I cannot sleep without this medicine.

Dependency-based inability.

슬퍼서 눈물을 참을 수 없었어요.

I was so sad I couldn't hold back my tears.

Internal emotional state.

그 광경을 보고 웃지 않을 수 없었다.

Looking at that sight, I couldn't help but laugh.

Double negative: -지 않을 수 없다 (must/couldn't help but).

부모님의 은혜는 다 갚을 수 없습니다.

One cannot fully repay the grace of one's parents.

Metaphorical impossibility of scale.

이것은 누구도 부정할 수 없는 사실입니다.

This is a fact that no one can deny.

Logical/Argumentative use.

상황이 너무 나빠서 손을 쓸 수 없어요.

The situation is so bad that nothing can be done.

Idiom: 손을 쓰다 (to take action/treat).

그의 제안을 거절할 수 없었습니다.

I could not refuse his proposal/offer.

Social/Professional pressure.

이 강을 건널 수 있는 방법이 없어요.

There is no way to cross this river.

Using '방법이 없다' as a synonym structure.

환경 오염은 더 이상 무시할 수 없는 문제입니다.

Environmental pollution is a problem that can no longer be ignored.

Formal/Societal context.

성공을 확신할 수 없는 상황입니다.

It is a situation where success cannot be guaranteed.

Expressing uncertainty.

인간의 욕심은 끝이 있을 수 없다.

There can be no end to human greed.

Philosophical statement.

이 이론은 과학적으로 증명될 수 없습니다.

This theory cannot be scientifically proven.

Passive form: 증명되다 + ㄹ 수 없다.

그의 공로는 아무리 강조해도 지나칠 수 없다.

His contribution cannot be overstated no matter how much it's emphasized.

Rhetorical structure: 아무리 ~해도 지나칠 수 없다.

이 두 사건은 별개로 생각할 수 없습니다.

These two events cannot be considered separately.

Logical connection.

그는 도저히 용납할 수 없는 실수를 저질렀다.

He committed an unforgivable (cannot be tolerated) mistake.

Adjectival use of the clause.

이 계약은 일방적으로 파기될 수 없습니다.

This contract cannot be unilaterally terminated.

Legal/Technical register.

전통은 하루아침에 만들어질 수 없는 것이다.

Tradition is something that cannot be made overnight.

Passive + Nominalization.

그 결과에 대해서는 책임을 피할 수 없을 것입니다.

One will not be able to avoid responsibility for that result.

Future conjecture: -을 것.

진리는 결코 왜곡될 수 없는 법이다.

Truth is something that can never be distorted.

Axiomatic expression: -는 법이다.

그의 문체는 누구도 흉내 낼 수 없는 독창성을 지녔다.

His writing style possesses an originality that no one can imitate.

High-level literary description.

역사의 흐름은 인위적으로 막을 수 있는 것이 아니다.

The flow of history is not something that can be stopped artificially.

Philosophical/Historical discourse.

그 조치는 돌이킬 수 없는 결과를 초래했다.

That measure brought about irreversible (cannot be turned back) results.

Idiomatic usage: 돌이킬 수 없는.

삶과 죽음의 경계는 명확히 구분 지을 수 없다.

The boundary between life and death cannot be clearly demarcated.

Abstract philosophical boundary.

민심은 천심이라, 이를 거스를 수 있는 권력은 없다.

The will of the people is the will of heaven; there is no power that can oppose it.

Proverbial/Political rhetoric.

예술의 가치는 돈으로 환산할 수 없는 영역에 존재한다.

The value of art exists in a realm that cannot be converted into money.

Abstract value assessment.

그의 결백을 증명할 길이 없어 안타까울 따름이다.

It is simply regrettable that there is no way (길이 없어) to prove his innocence.

Using '길이 없다' as a high-level variant.

Common Collocations

믿을 수 없다

참을 수 없다

잊을 수 없다

이해할 수 없다

비교할 수 없다

거절할 수 없다

피할 수 없다

예측할 수 없다

상상할 수 없다

멈출 수 없다

Common Phrases

어쩔 수 없다

— It can't be helped; there is no other choice.

이미 늦었으니 어쩔 수 없어요.

말할 수 없이

— Inexpressibly; beyond words.

말할 수 없이 기뻐요.

할 수 없지

— Well, nothing can be done (accepting a situation).

매진됐어? 할 수 없지.

도저히 갈 수 없다

— Simply cannot go no matter what.

몸이 아파서 도저히 갈 수 없어요.

다 셀 수 없다

— Innumerable; cannot count them all.

별이 너무 많아서 다 셀 수 없어요.

두고 볼 수 없다

— Cannot just stand by and watch (usually something bad).

불의를 보고 그냥 두고 볼 수 없었다.

참을 수 없는 존재의 가벼움

— The Unbearable Lightness of Being (Famous book title).

그 책의 제목은 '참을 수 없는 존재의 가벼움'이다.

가만히 있을 수 없다

— Cannot stay still; must take action.

가만히 있을 수 없어서 밖으로 나갔다.

믿기지 않을 수 없다

— Cannot help but be unbelievable (Double negative).

그의 성공은 믿기지 않을 수 없다.

부정할 수 없는

— Undeniable.

그것은 부정할 수 없는 증거입니다.

Often Confused With

ㄹ/을 수 없다 vs 못

못 is shorter and more casual; ㄹ 수 없다 is more formal and objective.

ㄹ/을 수 없다 vs -지 못하다

-지 못하다 often implies a desire to do something but being unable; ㄹ 수 없다 is a general lack of possibility.

ㄹ/을 수 없다 vs -(으)ㄹ 줄 모르다

This refers specifically to not knowing the 'how-to' or skill, whereas ㄹ 수 없다 can be about external circumstances.

Idioms & Expressions

"손을 쓸 수 없다"

— To be beyond help or repair; cannot take action.

불이 너무 커져서 손을 쓸 수 없었다.

Neutral

"눈 뜨고 볼 수 없다"

— To be too terrible or pathetic to watch.

그의 연기는 눈 뜨고 볼 수 없었다.

Informal

"입을 다물 수 없다"

— To be so surprised that one's mouth stays open.

놀라운 광경에 입을 다물 수 없었다.

Neutral

"발을 붙일 수 없다"

— To be unable to find a place or stand one's ground.

경쟁이 심해서 이곳에 발을 붙일 수 없다.

Metaphorical

"숨을 쉴 수 없다"

— To be extremely busy or under heavy pressure.

업무가 많아서 숨을 쉴 수 없을 정도예요.

Casual

"고개를 들 수 없다"

— To be too ashamed to look up.

창피해서 고개를 들 수 없었습니다.

Neutral

"말문이 막혀서 말을 할 수 없다"

— To be speechless (word-gate is blocked).

너무 당황해서 말을 할 수 없었다.

Neutral

"발 디딜 틈이 없다"

— To be so crowded that one cannot even step (related to ability to move).

지하철에 발 디딜 틈이 없어요.

Common

"어디 내놔도 손색이 없다"

— To be so good that it cannot be shamed anywhere (cannot lack anything).

이 실력은 어디 내놔도 손색이 없다.

Praising

"앞뒤를 가릴 수 없다"

— To be unable to distinguish front from back (acting recklessly).

화가 나서 앞뒤를 가릴 수 없었다.

Behavioral

Easily Confused

ㄹ/을 수 없다 vs 안 하다

Both are negative.

'안 하다' is 'to not do' (choice), while '할 수 없다' is 'cannot do' (inability).

공부를 안 해요 (I don't study by choice) vs 공부를 할 수 없어요 (I can't study due to noise).

ㄹ/을 수 없다 vs 못하다

Sounds similar.

'못하다' as a verb means 'to be bad at', while 'ㄹ 수 없다' means 'cannot'.

노래를 못해요 (I'm a bad singer) vs 노래를 할 수 없어요 (I can't sing because my throat hurts).

ㄹ/을 수 없다 vs 없다

Both mean 'not exist'.

'없다' is for objects/existence; 'ㄹ 수 없다' is for the possibility of an action.

돈이 없어요 (No money) vs 살 수 없어요 (Cannot buy).

ㄹ/을 수 없다 vs 모르다

Both show lack of something.

'모르다' is lack of knowledge; 'ㄹ 수 없다' is lack of possibility.

방법을 몰라요 (Don't know the way) vs 갈 수 없어요 (Can't go).

ㄹ/을 수 없다 vs 어렵다

Used as euphemisms.

'어렵다' means difficult; 'ㄹ 수 없다' means impossible.

풀기 어려워요 (Hard to solve) vs 풀 수 없어요 (Can't solve).

Sentence Patterns

N을/를 V-(으)ㄹ 수 없어요.

김치를 먹을 수 없어요.

Reason(-아서/어서) V-(으)ㄹ 수 없어요.

비가 와서 갈 수 없어요.

도저히 V-(으)ㄹ 수 없어요.

도저히 믿을 수 없어요.

V-지 않을 수 없었다.

웃지 않을 수 없었다.

아무리 ~해도 V-(으)ㄹ 수 없다.

아무리 노력해도 잊을 수 없다.

V-(으)ㄹ 수 없는 N

믿을 수 없는 이야기

N(이)라 V-(으)ㄹ 수 있는 권력이 없다.

민심을 거스를 수 있는 권력은 없다.

V-(으)ㄹ 수 없게 되다.

갑자기 갈 수 없게 됐어요.

Word Family

Nouns

수 (possibility/way)

불가능 (impossibility)

Verbs

없다 (to not exist)

못하다 (to be unable)

Adjectives

불가능하다 (impossible)

ㄹ 수 있다 (can)

ㄹ 리가 없다 (no way that)

ㄹ 줄 모르다 (not know how to)

ㄹ 필요가 없다 (no need to)

ㄹ 지경이다 (to the point of)

How to Use It

frequency

Extremely high in both spoken and written Korean.

Common Mistakes

먹었을 수 없어요 → 먹을 수 없었어요
The past tense must be on '없다', not on the main verb stem.
살을 수 없어요 → 살 수 없어요
For stems ending in 'ㄹ', do not add '을'. Just add '수 없다'.
할수없다 → 할 수 없다
There must be spaces between the modifier, the bound noun '수', and the verb '없다'.
수영할 수 못해요 → 수영할 수 없어요
You cannot combine 'ㄹ 수' with '못해요'. Choose one or the other.
추울 수 없어요 → 춥지 않아요 / 추울 리가 없어요
Adjectives usually don't use the potential form for simple negation.

Tips

Spacing Rule

Always remember the space: [Verb-ㄹ/을] [space] 수 [space] 없다. It's a common mistake even for natives in casual chat!

Softening a 'No'

If '갈 수 없어요' feels too harsh, try '가기 어려울 것 같아요' (It seems difficult to go) to be more polite.

Formal Contexts

In essays or business emails, use '-(으)ㄹ 수 없습니다' instead of '못' to maintain a professional tone.

Emphasis Adverbs

Pair it with '도저히' (not possibly) to express that you've tried everything but still can't do it.

Listen for the 'ㄹ'

The tiny 'ㄹ' sound at the end of the verb stem is your biggest clue that a potential structure is coming.

Ability vs. Circumstance

Remember it covers both: 'I can't swim' (ability) and 'I can't swim today because the pool is closed' (circumstance).

Declining Invitations

Koreans often use this to shift the reason for declining away from their own choice, making it more polite.

Watch the 'ㄹ' Verbs

For verbs like '만들다', don't add another '을'. It's just '만들 수 없다'.

The 'Su' Bridge

Imagine 'Su' is a bridge. 'Eopda' means the bridge is gone. You can't cross!

Double Negatives

Learn '-지 않을 수 없다' (cannot help but) to sound like a high-level speaker.

Memorize It

Mnemonic

Think of 'Su' as 'Superpower'. If you have 'Su-eopda' (Su-absent), you have NO superpower to do the action!

Visual Association

Imagine a road with a giant 'X' on it. The road is the 'Su' (the way), and the 'X' is 'Eopda' (not there/blocked).

Word Web

가다 (Go) -> 갈 수 없다 먹다 (Eat) -> 먹을 수 없다 하다 (Do) -> 할 수 없다 보다 (See) -> 볼 수 없다 듣다 (Hear) -> 들을 수 없다 웃다 (Laugh) -> 웃을 수 없다 울다 (Cry) -> 울 수 없다 자다 (Sleep) -> 잘 수 없다

Challenge

Try to list 5 things you cannot do today because of the weather using 'ㄹ 수 없어요'.

Word Origin

The phrase originates from the combination of the future-oriented modifier '-ㄹ', the bound noun '수' (derived from Middle Korean meaning 'way' or 'method'), and the negative verb '없다'.

Original meaning: Literally: 'The way/method (to do something in the future) does not exist.'

Koreanic (Native Korean grammar construction).

Cultural Context

When declining an invitation from a superior, it is better to say '-기 어려울 것 같습니다' (It seems it will be difficult) rather than a blunt '갈 수 없습니다,' which can sound too final.

English speakers often over-rely on '못' because it's shorter, but using 'ㄹ 수 없다' makes you sound much more fluent and educated in formal or semi-formal Korean settings.

The song '잊을 수 없어' (Cannot Forget) by various artists. The movie title '참을 수 없는' (Unbearable). Commonly seen on 'No Parking' signs: '주차할 수 없습니다'.

Practice in Real Life

Real-World Contexts

Declining an invitation

선약이 있어서 갈 수 없어요.
일이 많아서 참여할 수 없습니다.
시간을 낼 수 없어요.
죄송하지만 갈 수 없게 됐어요.

Reporting a problem

기계가 작동할 수 없어요.
인터넷을 연결할 수 없습니다.
파일을 열 수 없어요.
소리가 들리지 않아 들을 수 없어요.

Expressing surprise

믿을 수 없는 일이에요!
상상할 수 없었어요.
그럴 수 없어요!
이해할 수 없는 행동이에요.

Physical limitations

매운 것을 먹을 수 없어요.
술을 마실 수 없습니다.
수영을 할 수 없어요.
운전을 할 수 없어요.

Public rules

여기서 사진을 찍을 수 없습니다.
음식물을 반입할 수 없어요.
들어갈 수 없습니다.
주차할 수 없어요.

Conversation Starters

"혹시 한국어를 할 수 없으신가요? (Can you not speak Korean?)"

"왜 오늘 파티에 올 수 없어요? (Why can't you come to the party today?)"

"믿을 수 없는 소식을 들었는데, 아세요? (I heard some unbelievable news, do you know?)"

"매운 음식을 전혀 먹을 수 없나요? (Can you not eat spicy food at all?)"

"이 문제를 도저히 풀 수 없는데 좀 도와줄래? (I simply can't solve this problem, can you help?)"

Journal Prompts

오늘 내가 하고 싶었지만 할 수 없었던 일 세 가지 적어보기. (Write three things I wanted to do today but couldn't.)

내가 절대로 잊을 수 없는 추억에 대해 써보기. (Write about a memory I can never forget.)

돈으로 살 수 없는 소중한 것은 무엇일까? (What is something precious that money cannot buy?)

미래에 내가 할 수 있게 되고 싶은 일은? (What is something I want to be able to do in the future?)

내가 이해할 수 없는 세상의 모습은? (What aspects of the world can I not understand?)

Frequently Asked Questions

10 questions

Generally, no. Adjectives describe states, not actions. Use '-지 않다' for negation or '-을 리가 없다' for logical impossibility. However, in some contexts like '행복할 수 없다' (cannot be happy), it is used to describe a state that is impossible to achieve.

'못 가요' is more common in spoken Korean and often sounds like a personal excuse. '갈 수 없어요' is more formal and sounds like an objective statement of fact. In writing, always prefer '갈 수 없습니다'.

Yes, in official Korean spelling, '수' is a bound noun, so it must be separated by a space from the modifier and the following verb. Incorrect: 할수없다. Correct: 할 수 없다.

You conjugate the final verb '없다' into the past tense '없었다'. Example: '먹을 수 없었어요' (I could not eat).

Usually, we use '-아/어도 돼요?' for 'May I?'. 'ㄹ 수 있어요?' is more about 'Is it possible?' or 'Do you have the ability?'. 'ㄹ 수 없어요?' is 'Can't you?' (expressing surprise).

It is a very common idiom meaning 'It can't be helped' or 'There's no other way.' It's used when accepting an unavoidable situation.

Yes. For 'ㄹ' stems (살다), it becomes '살 수 없다'. For 'ㄷ' stems (듣다), it becomes '들을 수 없다'. For 'ㅂ' stems (돕다), it becomes '도울 수 없다'.

Yes, 'ㄹ 수 없다' often sounds more definitive and absolute regarding the impossibility of the action.

Yes, '전혀 ... ㄹ 수 없다' means 'cannot ... at all' and is very common for emphasis.

It is almost always in the '-습니다' form: '주차할 수 없습니다' (No parking), '입장할 수 없습니다' (No entry).