-ㄴ/는/ㄹ 게 틀림없다
Be Certain/sure
'-ㄴ/는/ㄹ 게 틀림없다' means 'it must be...' or 'it's certain that...'. It's a strong statement of conviction.
How It Works
'-ㄴ/는/ㄹ 게 틀림없다' is a powerful expression used to state that something is undoubtedly true. The phrase '틀림없다' literally means 'there is no mistake/error,' so the entire pattern translates to 'the fact that... is without error,' or more naturally, 'it must be that...' or 'I'm sure that...'.
This pattern is used when the speaker is making a logical deduction based on strong evidence, not just a simple guess.
Conjugation Rules:
The pattern attaches to the noun-modifying forms of verbs and adjectives.
1. Adjectives (Present Tense):
- Stems ending in a vowel: -ㄴ 게 틀림없다 (e.g., 예쁘다 → 예쁜 게 틀림없다)
- Stems ending in a consonant: -은 게 틀림없다 (e.g., 좋다 → 좋은 게 틀림없다)
2. Verbs (Present Tense):
- Always use -는 게 틀림없다 regardless of the stem. (e.g., 먹다 → 먹는 게 틀림없다; 가다 → 가는 게 틀림없다)
3. Past Tense:
The past tense has different forms depending on the nuance.
A. Completed Action (Verbs): Used to state certainty about an action that is verifiably finished. This uses the past tense noun-modifying form.
- Stems ending in a vowel: -ㄴ 게 틀림없다 (e.g., 보다 → 본 게 틀림없다 - It's certain that they saw it)
- Stems ending in a consonant: -은 게 틀림없다 (e.g., 먹다 → 먹은 게 틀림없다 - It's certain that they ate it)
B. Past State (Adjectives & 이다): Used to state certainty about a state that was true in the past.
- Use -았/었던 게 틀림없다 (e.g., 예쁘다 → 예뻤던 게 틀림없다 - It's certain she was pretty; 학생이다 → 학생이었던 게 틀림없다 - It's certain he was a student)
C. Conjecture about a Past Event (Verbs & Adjectives): Used to express a strong deduction that something must have happened or must have been true.
- Attach -았/었을 게 틀림없다 to the stem. (e.g., 오다 → 왔을 게 틀림없다 - It must have rained; 바쁘다 → 바빴을 게 틀림없다 - He must have been busy)
4. Future Tense / Conjecture (Verbs & Adjectives):
- Stems ending in a vowel: -ㄹ 게 틀림없다 (e.g., 오다 → 올 게 틀림없다)
- Stems ending in a consonant: -을 게 틀림없다 (e.g., 먹다 → 먹을 게 틀림없다)
5. Nouns (with 이다):
- Present: Noun + 인 게 틀림없다 (e.g., 학생이다 → 학생인 게 틀림없다)
- Past: See rule 3B above.
This pattern is much stronger than -ㄴ/는/ㄹ 것 같다 ('it seems like') or -나 보다 ('I guess'). It should only be used when you have a high degree of confidence.
Examples (6)
- 저렇게 환하게 웃는 걸 보니 기분이 좋은 게 틀림없어요.
Seeing them smile so brightly, they must be in a good mood.
Word by Word: Seeing (them) smiling brightly like that, (their) mood being good is certain.
- 매일 밤 늦게까지 불이 켜져 있는 걸 보면, 저 집 학생은 열심히 공부하는 게 틀림없다.
Seeing the lights on late every night, the student in that house must be studying hard.
Word by Word: Seeing the light is on until late every night, that house's student studying hard is certain.
- 바닥이 젖어 있는 걸 보니 밤사이에 비가 왔을 게 틀림없다.
Seeing that the ground is wet, it must have rained during the night.
Word by Word: Seeing the floor is wet, during the night rain must have come is certain.
Here, '-았/었을 게 틀림없다' is used to make a strong conjecture about a past event (raining).
- 이 서류는 그 사람이 직접 작성한 게 틀림없습니다.
This document must have been written by that person himself.
Word by Word: This document, that person directly wrote is certain.
This uses the '-ㄴ/은 게 틀림없다' form to express certainty about a completed past action (작성하다 → 작성한).
- 그의 말투를 들어보니 한국 사람인 게 틀림없어요.
Listening to his accent, he must be Korean.
Word by Word: Listening to his way of speaking, (him) being a Korean person is certain.
This example shows the pattern used with a noun + 이다 (사람이다 → 사람인 게).
- 이렇게 많은 사람들이 모인 것을 보니, 내일 경기는 재미있을 게 틀림없다.
Seeing so many people gathered, tomorrow's game is sure to be exciting.
Word by Word: Seeing that this many people have gathered, tomorrow's game being interesting is certain.
This uses the future/conjecture form '-을 게 틀림없다' to express certainty about a future event.
Common Mistakes
Using it for a weak guess instead of a strong conviction.
Different Meaning하늘이 조금 흐리니까 비가 올 게 틀림없어요.Better하늘이 조금 흐리니까 비가 올 것 같아요.'-ㄴ/는/ㄹ 게 틀림없다' implies near 100% certainty based on strong evidence (like dark storm clouds and thunder). For a simple guess based on slightly cloudy skies, use a softer expression like -ㄹ 것 같다.
Using the present tense form for a past event.
Not Quite어제 그가 여기 오는 게 틀림없다.Better어제 그가 여기 왔을 게 틀림없다.To express certainty about a past event, you must use a past tense form. Use '-ㄴ/은 게 틀림없다' for a completed action you are certain of (e.g., '그가 여기 온 게 틀림없다') or '-았/었을 게 틀림없다' for a strong deduction about a past event. The present tense form '오는 게' cannot be used with a past time marker like '어제'.
Learn This First
To express certainty 'be certain/sure', you need modifier forms and negation concepts.
Related Patterns
- -ㄴ/는/ㄹ 것 같다Seems Like, Looks Like
Both express inference, but '-ㄴ/는/ㄹ 게 틀림없다' indicates a much stronger degree of certainty ('it must be'), while '-ㄴ/는/ㄹ 것 같다' is for a guess or assumption ('it seems like').
- -(으)ㄹ 리가 없다There's No Way, Impossible
This is the logical opposite. While '-ㄴ/는/ㄹ 게 틀림없다' means 'it's certain that...', '-ㄹ 리가 없다' means 'there's no way that...' or 'it's impossible that...'. Both express strong conviction.
- -나 보다It Seems/looks Like
Similar to '-ㄴ/는/ㄹ 것 같다', '-나 보다' is used for guessing based on observation ('I guess/suppose'). It is much weaker and more colloquial than the very certain '-ㄴ/는/ㄹ 게 틀림없다'.
- -ㄴ/는/ㄹ 게 뻔하다It's Obvious/certain That
Very similar in meaning, expressing certainty. However, '-ㄴ/는/ㄹ 게 뻔하다' often carries a negative nuance, implying that the outcome is obvious and often undesirable. '-ㄴ/는/ㄹ 게 틀림없다' is more neutral.
- -는 것Thing of -ing
This pattern uses the nominalizing form '-는 것' (shortened to '-는 게'). Understanding how -는 것 turns a verb or adjective clause into a noun phrase is essential for understanding the structure of '-ㄴ/는/ㄹ 게 틀림없다'.