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Korean Negation 안 vs 못: Fix the "Can't vs Won't" Mistake

안 vs 못 look similar but mean opposite things — choice vs inability. Learn the rule and stop reversing your own story. Try free at kdiaryai.com.

For Korean learners at beginner to intermediate level

You wanted to say "I couldn't sleep" and wrote 안 잤어요. A native speaker read it as "I chose not to sleep." Different sentence, different vibe — and nobody corrected you, so the mistake just... stayed.

This is one of the most common silent errors in Korean writing. Here's the fix.

The Short Answer

안 negates by choice — you didn't do it, could have, but didn't. 못 negates by inability — you couldn't do it, no matter what you wanted.

Both go right before the verb. The difference is entirely in why the thing didn't happen.

The Practical Rule

Use 안 when:

  • It was a decision, not a limitation
  • You're describing a habit or preference
  • The "why" is irrelevant or implied to be intentional

저는 커피를 안 마셔요. — I don't drink coffee. (choice, preference)

Use 못 when:

  • Something outside your control stopped you
  • You want to, but circumstances say no
  • You're explaining a limitation, not a decision

어제 잠을 못 잤어요. — I couldn't sleep last night. (insomnia, noise, stress — not a choice)

Side by Side

저는 매운 음식을 안 먹어요. — I don't eat spicy food. (I choose not to — maybe I don't like it)

저는 매운 음식을 못 먹어요. — I can't eat spicy food. (I physically can't handle it — stomach, allergy)

Same object, same verb, completely different reason. A reader can't tell which one you mean unless you pick the right particle.

The One Exception That Trips Everyone Up

With 하다 verbs (like 공부하다, 운동하다), 못 splits the word in two:

공부 못 했어요. — I couldn't study. (NOT 공부하지 못했어요's shortcut — 못 goes between the noun and 하다)

This is why 못공부했어요 looks wrong even to beginners — 못 needs its own space before 하다.

Why This Matters for Writing

When you write a Korean diary about your day, you're constantly explaining why things did or didn't happen — "I didn't go out," "I couldn't finish," "I didn't call." Pick 안 when it was your call. Pick 못 when it wasn't. Mixing them up doesn't confuse meaning entirely, but it quietly reverses the story you're telling about yourself — from "chose not to" to "tried and failed," or the other way around.

That distinction is exactly the kind of thing self-correction misses, because both sentences feel grammatical when you write them.

Write a Korean diary entry today and find out whether your 안 and 못 are telling the story you meant. Try Korean Diary AI →

Recommended for Grammar Practice

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Negation patterns need repeated contrastive practice to stick. These books cover it directly: