One aspect of Korean that seems to cause issues for beginners is how to correctly say they will not/cannot do something. (Personally, I feel I use them correctly, but this is a really common issue I came across when teaching beginners Korean, hence my asking the question for the general public).

What are the proper usages for the endings -지 않다 (지 아니하다), -지 못하다, and -ㄹ/을 수 없다?

For example, if I want to tell a coworker that I have not eaten yet because I was too busy, should I say "너무 바빠서 아직 먹지 못 했어요" or should I say "너무 바빠서 아직 먹지 않았어요"?

(Alternatively in the short form, the sentences above can be "너무 바빠서 아직 못 먹었어요" and "너무 바빠서 아직 안 먹었어요")

How does the -ㄹ/을 수 없다 ending play into this conversation of negating a verb, and when is it appropriate?

2 Answers 2


The little nuances could make for a very long and detailed answer, but the general rules are along these lines:

  • ~지 않다 (And by extension, 안 하다)
    • On a 동사/Action Verb
      • One doesn't do something, regardless of whether it's possible or not.
      • Very often implies (with strength of the implication depending on context) deliberatly not doing something. But it doesn't automatically confer actual deliberateness in all cases.

        저는 가지 않았어요 => "I didn't go"

    • (on a 형용사/Adjective)
      • One isn't something, again regardless of whether it is possible to be .

        저는 똑똑하지 않아요 => "I am not smart."

  • ~지 못하다 (And by extension, 못 하다)

    • One can't do/be something.
    • Does not imply that the action is impossible, rather, it implies that the action couldn't be done perhaps due to circumstances, but may otherwise be possible.

      못 들었어요 => "I couldn't/didn't hear you."

      못 갈 거예요 => "I won't be able to go."

  • ~ㄹ 수 없다
    • This implies that something is actually impossible (or if context is specific, is impossible within that context.)

      인간은 날 수 없어요 => Humans cannot fly.

There is at least one important extra nuance to note, however. Many words, such as 보다 or 듣다 will have stronger implications of deliberateness when using between ~지 않다 instead of ~지 못하다:

Also, 듣다 specifically (and surely many other words that are hard to summarize) has a pretty important distinction in meaning depending on context. It's hard to get the feeling when translating, but for a general idea:

듣지 않았어요 => I didn't listen to it. (Sort of strong implication that this is intentional or by oversight)

듣지 못했어요 => I couldn't hear it.

  • Not sure if I'm right, but 못 also implies that you want to do something, or at least there's an obligation to do it even if you don't want to, right?
    – busukxuan
    Commented Jun 23, 2016 at 17:17
  • Regarding the discussion about 듣다, it's much more common to hear the negative using the passive verb (들리다) producing 안 들려요 for "I couldn't hear it." In fact, I asked a native speaker, and was told 듣지 못했어요 is not correct. Would be great to others' opinions about this and we should maybe update this answer. Commented May 27, 2017 at 22:38
  • @ryanbrainard a native I asked was fine with '듣지 못했어요'. Google searches for "듣지 못했어요" and "듣지 못했어" bring up quite a lot of hits (which may not mean technical correctness, of course!) Commented May 28, 2017 at 8:34
  • @topomorto Interesting. Did you happen to ask about comparing it to 안 들려요? Commented May 28, 2017 at 10:09
  • @ryanbrainard their initial instinct was that 안 들려요, 못 들었어요, 듣지 못했어요 could logically mean similar things in some contexts. I'm sure there are plenty of reasons why one of those options might be more natural or preferable in various particular situations. I think I do hear '안 들려' more often. Commented May 28, 2017 at 11:20

안 = don't (않 = 안하(다)/아니하(다), 안 = 아니 )

못 = can't

없다 = be not

1. 안, 못 with/without space.

And there are also verbs with 안, 못. for example,

안되다 = poor

안 되다 = doesn't work

못하다 = be not good at

못 하다 = can't do

못생기다 = be ugly

못 생기다 = can't create

2. 있다 / 없다


There is/are ~ = ~이/가 있다.

S be-verb ~ = S이/가 있다.

(possibility / ability)

be able to / can / could / may / might = -ㄹ 수 있다

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