못 vs 안: Which Korean "Not" Does Your Sentence Need?
못 means can't, 안 means doesn't — and the wrong one changes what you said. The rule, the traps, and practice at kdiaryai.com.
For Korean learners at beginner to intermediate level
A student wrote this sentence about a phrase that had fallen out of fashion:
❌ 이 말이 요즘은 많이 보이지 못하는 것 같다.
Their intent was simple: "This phrase doesn't seem to get used much these days."
Nothing here is misspelled. The grammar of 보이지 못하다 is textbook-correct. But a native reader stops, because the sentence says something the writer never meant — that the phrase is somehow unable to appear. As if it were trying and failing.
The natural version:
✅ 이 말이 요즘은 많이 쓰이지 않는 것 같다.
Two things changed. The verb, and — more importantly — which kind of "not" was used.
The Rule, in One Line
안 / -지 않다 = doesn't. 못 / -지 못하다 = can't.
English blurs these. Korean does not.
- 안 is about fact or choice. It simply didn't happen, or you don't do it.
- 못 is about an obstacle. Something outside your will blocked it.
Once you hear it this way, the student's sentence gives itself away. A phrase falling out of fashion isn't blocked from appearing. People just stopped using it. That's 안, not 못.
The Pair That Makes It Click
Keep these two sentences somewhere you can see them. Almost every mistake with 못 is a version of this pair:
| Korean | English | What it implies |
|---|---|---|
| 오늘 일기를 안 썼어요. | I didn't write my diary today. | I just didn't. No drama. |
| 오늘 일기를 못 썼어요. | I couldn't write my diary today. | Something stopped me — work, no time, I was sick. |
Both are correct Korean. They are not interchangeable. The second one quietly asks to be explained: why couldn't you?
More pairs, same logic:
| 안 (doesn't) | 못 (can't) |
|---|---|
| 술을 안 마셔요. — I don't drink. | 술을 못 마셔요. — I can't drink (it doesn't agree with me). |
| 매운 음식을 안 먹어요. — I don't eat spicy food. | 매운 음식을 못 먹어요. — I can't handle spicy food. |
| 그 사람을 안 만났어요. — I didn't meet them. | 그 사람을 못 만났어요. — I couldn't meet them (we missed each other). |
Notice how the 못 column always leaves a small hole in the story. That hole is the meaning.
Why English Speakers Reach for 못
Because English "can't" is soft. We say "I can't come tonight" when we simply have other plans. We say "I couldn't finish it" when we ran out of interest.
Korean 못 doesn't stretch that far. It means an actual barrier existed. So when you translate your English "couldn't" straight into 못, you often overstate your case — you claim you were prevented when you merely didn't.
A quick self-test: ask yourself "Was something in my way?" If you can't name the obstacle, use 안.
The Trap in the Other Direction
The fix isn't "always use 안." 못 is exactly right when a real barrier exists:
- 표가 다 팔려서 영화를 못 봤어요. — The tickets sold out, so I couldn't see the film.
- 비가 와서 산책을 못 했어요. — It rained, so I couldn't take a walk.
- 한국어를 아직 잘 못 해요. — I still can't speak Korean well.
That last one is worth pausing on. 못 is the honest word for "not yet able." Learners sometimes avoid it out of caution and write 잘 안 해요 instead — which means "I don't do it well on purpose." That's a stranger sentence than the mistake they were avoiding.
Three Places 못 Simply Cannot Go
1. With descriptive verbs (adjectives).
Ability doesn't apply to a state. A room cannot fail to be clean.
- ❌ 방이 못 깨끗해요.
- ✅ 방이 안 깨끗해요. — The room isn't clean.
2. With verbs that already have a negative twin.
Korean has dedicated negative words for a few high-frequency verbs. Don't build your own.
| Positive | Negative | Never write |
|---|---|---|
| 있다 | 없다 | 안 있다 |
| 알다 | 모르다 | 안 알다 |
| 좋다 | 싫다 (as a preference) | — |
3. Inside a 하다 verb.
With noun + 하다, the negator goes between the two parts, not in front of the whole word.
- ❌ 안 운동해요 / ❌ 못 공부했어요
- ✅ 운동 안 해요 — I don't exercise.
- ✅ 공부 못 했어요 — I couldn't study.
Short Form vs Long Form
Both negators have two shapes, and they mean the same thing:
| Short | Long | |
|---|---|---|
| doesn't | 안 먹어요 | 먹지 않아요 |
| can't | 못 먹어요 | 먹지 못해요 |
The short form sounds lighter and more spoken. The long form is a little more formal and more common in writing — which is why the corrected sentence above used 쓰이지 않는다 rather than 안 쓰인다. In a diary, either is fine. Pick the one that sounds like you.
The Other Half of That Correction
The student's sentence had a second problem worth naming, because it's the same kind of error one level down.
They wrote 보이다 (to be seen) where the meaning called for 쓰이다 (to be used).
- 보이지 않다 — isn't visible. You'd use it for a mountain hidden by fog.
- 쓰이지 않다 — isn't used. You'd use it for a word, a tool, a room.
A phrase that has gone out of fashion is not invisible. It's unused. Same instinct as 못 vs 안: choose the word that names what actually happened, not the one that feels roughly close.
Try It Yourself
Fill in 안 or 못, then check your reasoning — not just your answer.
- 어제 너무 바빠서 친구한테 전화를 ___ 했어요.
- 저는 커피를 ___ 마셔요. 그냥 차를 더 좋아해요.
- 그 단어는 요즘 거의 ___ 쓰여요.
- 못 — "too busy" is a real obstacle.
- 안 — no barrier at all; it's a preference. 못 would mean caffeine makes you ill.
- 안 — a word going unused is a fact about people's habits, not an inability. This is the student's original sentence, fixed.
The Takeaway
Before you write a negative sentence in Korean, ask one question: am I saying it didn't happen, or that it couldn't?
English lets you skip that question. Korean asks it every time — and answers it out loud, in a single syllable, whether you meant to or not.
Writing your own diary entries is the fastest way to find out which one you reach for by default. Write a few sentences about something you didn't do this week, and get them corrected at kdiaryai.com — the 못/안 slip is one of the first things a correction will surface.