-지 못하다: Can't, and Why It's the Kinder Refusal

못 means cannot. Its long form, -지 못하다, means the same thing in a more written register — the same split you already met with 안 and -지 않다.

The reason this deserves its own page is not the grammar. It is the social work the word does.

Building it

못 + verb              short, spoken
verb stem + -지 못하다  long, written

가다   →  못 가요    /  가지 못해요
먹다   →  못 먹어요  /  먹지 못해요

And 하다 verbs split, exactly as they do with 안:

공부하다  →  공부 못 해요   ✅
          →  못 공부해요    ❌

If you learned the 안 rule, you already know this one.

안 versus 못

안 — you are not doing it. A choice.
못 — you cannot do it. An obstacle.

안 가요.   I'm not going.     (I decided not to)
못 가요.   I can't go.        (something prevents me)

This is a real distinction, not a nuance. 수영 안 해요 means you do not swim — perhaps you dislike it. 수영 못 해요 means you cannot swim.

The part worth knowing

Koreans very often use 못 to refuse things, even when the real reason is choice.

A: 내일 같이 갈래요? — Want to come tomorrow?
B: 아, 내일은 못 가요. 미안해요. — Ah, I can’t tomorrow. Sorry.

B may simply not want to go. Saying 안 가요 — I’m not going — states a decision, and that lands harder than most speakers intend. 못 가요 puts the reason outside the speaker, leaving the refusal soft and unexplained.

English does the same thing with “I can’t make it” instead of “I don’t want to.” Korean just leans on it more.

For a learner this matters practically: when you turn down an invitation, reach for 못. The full pattern is usually:

아, 내일은 좀… 못 갈 것 같아요. 다음에 봐요!

Trailing off with 좀… and adding 다음에 (next time) is standard. Turning something down flatly is unusual in Korean, and 못 is the grammar that lets you avoid it.

Pronunciation

못 does not sound the way it is spelled.

Before ㅁ and ㄴ, the final ㅅ becomes ㄴ. Elsewhere it is [몯] and often tenses the following consonant. Nobody expects you to derive this — just know that what you hear will not match what you see.

Not for adjectives

못 describes being prevented, and you cannot be prevented from a state.

못 예뻐요.   ❌
안 예뻐요.   ✅

A few 하다 adjectives are exceptions where 못 works idiomatically, but as a rule: adjectives take 안.

And -을 수 없다

There is a third way to say “cannot”, which comes later in the course:

갈 수 없어요 — I can’t go. (more neutral, often more formal)

It overlaps with 못 almost entirely. 못 is more personal and immediate; -을 수 있다 in the negative is flatter and states impossibility as a fact. Both are correct, and beginners can safely use 못.