-(으)ㄹ 줄 알다 / 모르다: Know How To | Korean Grammar

-(으)ㄹ 줄 알다 means "know how to," and -(으)ㄹ 줄 모르다 means "not know how to." Like -(으)ㄹ 수 있다, it is built on a bound noun — here 줄, roughly "the way / the method / the manner of doing" — but it locks onto a much narrower meaning: skill, know-how, learned competence. That narrowness is the whole point of the page, because English speakers habitually collapse "know how to" and "can" into the one word can, and Korean keeps them apart.

The construction

Attach the prospective modifier -(으)ㄹ to the verb, add the bound noun 줄 (spaced), then 알다 ("know") or 모르다 ("not know"):

Verb	-(으)ㄹ 줄 알다	Meaning
수영하다	수영할 줄 알아요	I know how to swim
운전하다	운전할 줄 몰라요	I don't know how to drive
읽다	읽을 줄 알아요	I know how to read (it)
만들다	만들 줄 알아요	I know how to make (it)

The batchim rule is identical to every other -(으)ㄹ construction: vowel or ㄹ-stem takes bare -ㄹ 줄 (할 줄, 만들 줄), a consonant stem takes -을 줄 (읽을 줄). Note the irregular contraction on 모르다: 모르다 → 몰라요 in the present (a 르-irregular), so "don't know how" is 몰라요, not ×모르아요.

저는 자전거를 탈 줄 알아요.

jeoneun jajeongeoreul tal jul arayo

I know how to ride a bike.

운전할 줄 몰라서 항상 지하철을 타요.

unjeonhal jul mollaseo hangsang jihacheoreul tayo

I don't know how to drive, so I always take the subway.

김치를 만들 줄 알아요?

gimchireul mandeul jul arayo

Do you know how to make kimchi?

The reframing: know-how vs ability

Here is the distinction that matters. -(으)ㄹ 줄 알다 highlights that you possess the skill — you have learned the technique and could, in principle, do it. -(으)ㄹ 수 있다 highlights that you are able / it is possible in the here and now, whether that's because you have the skill or because circumstances permit.

저는 수영할 줄 알아요.

jeoneun suyeonghal jul arayo

I know how to swim. (I have the skill)

오늘은 수영할 수 있어요.

oneureun suyeonghal su isseoyo

I can swim today. (it's possible — the pool is open, I have time)

The clearest way to feel the gap is a sentence where the skill and the possibility come apart: you have the skill but can't exercise it right now.

수영할 줄은 아는데 오늘은 감기 때문에 수영할 수 없어요.

suyeonghal jureun aneunde oneureun gamgi ttaemune suyeonghal su eopseoyo

I do know how to swim, but I can't today because I have a cold.

That sentence is impossible to say with a single English word, and it is impossible to say in Korean with 줄 알다 alone. "I can't swim today (I'm sick)" is about possibility, so it must be 수 없어요 — never ×수영할 줄 몰라요, which would falsely claim you never learned. This is the number-one error learners make with 줄 알다, so hold onto it.

💡

Ask: "Am I talking about a skill I have learned (줄 알다), or about whether it's possible / I'm able right now (수 있다)?" A cold, a closed pool, a lack of time all block possibility (수 있다), not know-how (줄 알다). Your swimming skill doesn't vanish because you have a cold.

한글은 읽을 줄 아는데 아직 잘 못 써요.

Hangeureun ilgeul jul aneunde ajik jal mot sseoyo

I know how to read Hangul, but I still can't write it well.

젓가락질할 줄 몰라서 포크로 먹었어요.

jeotgarakjilhal jul mollaseo pokeuro meogeosseoyo

I don't know how to use chopsticks, so I ate with a fork.

The second life: -(으)ㄴ/는 줄 알았다 = "thought / assumed that"

Now the twist that surprises everyone. When 줄 알다 appears with a past or present modifier (-(으)ㄴ or -는) rather than the prospective -(으)ㄹ, and especially in the past tense 알았다, it stops meaning "know how" entirely. Instead it means "thought / assumed (mistakenly) that":

가게 문을 닫은 줄 알았어요.

gage muneul dadeun jul arasseoyo

I thought the shop was closed.

저는 그 사람이 선생님인 줄 알았어요.

jeoneun geu sarami seonsaengnimin jul arasseoyo

I thought that person was a teacher.

벌써 끝난 줄 알았어요.

beolsseo kkeunnan jul arasseoyo

I thought it was already over.

💡

The tense is your giveaway. Present 줄 알아요 / 몰라요 with a -(으)ㄹ modifier = "know / don't know how to." Past 줄 알았어요 with a -(으)ㄴ/-는 modifier = "(mistakenly) thought that." If you see 알았어요 plus a past modifier, it's almost never about skill.

The strong implication is that the belief turned out to be wrong: the shop was actually open, the person wasn't a teacher, it wasn't over yet. This is a genuinely different construction — a mistaken-belief marker — and it happens to reuse the same 줄 알다 skeleton. What tells the two apart is the modifier: prospective -(으)ㄹ 줄 알다 = "know how to"; past/present -(으)ㄴ/-는 줄 알았다 = "assumed that." It sits alongside the quotation and reported-thought system, so if you want to explore how Korean packages beliefs and reported speech, start at the quotation overview.

For the bound noun 줄 on its own — its meaning and its cousins — see the bound noun 줄.

Common Mistakes

1. Using 줄 알다/모르다 for situational possibility. Whether you can do something today (time, weather, permission) is 수 있다/없다, not know-how.

❌ 오늘 시간이 있어서 갈 줄 알아요.

Wrong — 'I can go today (I have time)' is possibility, not a skill.

✅ 오늘 시간이 있어서 갈 수 있어요.

oneul sigani isseoseo gal su isseoyo

I can go today because I have time.

2. Saying "I can't do it today" with 줄 모르다. That falsely denies the skill; use 수 없다.

❌ 감기 때문에 수영할 줄 몰라요.

Wrong — this claims you never learned to swim, not that you can't today.

✅ 감기 때문에 수영할 수 없어요.

gamgi ttaemune suyeonghal su eopseoyo

I can't swim today because of a cold.

3. Dropping 줄 and using bare 알다 for "know how." 알다 alone means "know (a fact)"; the know-how sense needs 줄.

❌ 저는 운전을 알아요.

Wrong for 'I know how to drive' — needs 운전할 줄 알아요.

✅ 저는 운전할 줄 알아요.

jeoneun unjeonhal jul arayo

I know how to drive.

4. Adding 을 to a ㄹ-stem. Same trap as everywhere: ㄹ-stems take bare -ㄹ 줄.

❌ 이 요리를 만들을 줄 알아요.

Incorrect — the ㄹ-stem takes 만들 줄, no 을.

✅ 이 요리를 만들 줄 알아요.

i yorireul mandeul jul arayo

I know how to make this dish.

5. Blurring "know how" and "assumed that" by using the wrong modifier. Prospective -(으)ㄹ for skill; past -(으)ㄴ for a mistaken belief.

❌ 문을 닫을 줄 알았어요.

Says 'I knew how to close the door' — but you mean you thought it was closed.

✅ 문을 닫은 줄 알았어요.

muneul dadeun jul arasseoyo

I thought the door was closed.

Key Takeaways

-(으)ㄹ 줄 알다 / 모르다 = "know / don't know how to" — a learned skill, built on the bound noun 줄.
Keep it apart from -(으)ㄹ 수 있다: 줄 알다 is know-how; 수 있다 is ability/possibility. You can know how to swim yet be unable to today.
모르다 contracts to 몰라요 (르-irregular), not ×모르아요.
With a past modifier, -(으)ㄴ 줄 알았다 flips to "assumed / thought (wrongly) that" — a different construction that shares the skeleton.

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