Long Inability: -지 못하다 | Korean Grammar

Korean's inability negation comes in two forms, exactly mirroring the two "not" forms. The quick one is the adverb 못, which you plant before the verb. The longer one is -지 못하다: attach -지 to the verb stem and follow it with the auxiliary 못하다, then conjugate that for tense and politeness. 가다 → 가지 못해요, 오다 → 오지 못했어요, 참석하다 → 참석하지 못했습니다. It means the same "can't / unable to" as short 못, but it's more formal, more written, and — like its cousin -지 않다 — it dodges the noun+하다 split.

How to build it: stem + 지 + 못하다

Drop -다 from the dictionary form to get the stem, add -지, then finish with a conjugated 못하다 (written as one word, no space inside it). The main verb is now frozen; 못하다 does all the tense-and-politeness work.

다리를 다쳐서 걷지 못해요.

darireul dacheoseo geotji motaeyo

I hurt my leg, so I can't walk.

그날은 사정이 있어서 오지 못했어요.

geunareun sajeong-i isseoseo oji motaesseoyo

I had something come up that day, so I couldn't make it.

끝까지 읽지 못했어요.

kkeutkkaji ikji motaesseoyo

I couldn't finish reading it.

The auxiliary 못하다 is pronounced [모타다] — the ㅅ of 못 fuses with the ㅎ of 하다 into an aspirated ㅌ, the same fusion you hear in the phrase 못 해요 [모태요]. So 못해요 → [모태요], 못했어요 → [모태써요]. The spelling stays 못하다, but say it with that ㅌ.

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Spacing tell: as the negation auxiliary here, 못하다 is one word (가지 못해요). Don't confuse it with the two-word 못 하다 you get from splitting a noun+하다 verb in the short form (공부 못 해요). In the long form 하다 always stays glued to 못.

Tense lives on 못하다, not the main verb

As with every -지 auxiliary construction, the past marker -았/었- attaches to the auxiliary, never to the main verb. The past of 가지 못하다 is 가지 못했어요 — never ×갔지 못해요. The main verb stays inert in its -지 form.

어제는 너무 피곤해서 운동하지 못했어요.

eojeneun neomu pigonhaeseo undonghaji motaesseoyo

I was too tired yesterday, so I couldn't work out.

시간이 없어서 준비하지 못했어요.

sigani eopseoseo junbihaji motaesseoyo

I ran out of time, so I couldn't prepare.

Hold the same image you use for -지 않다: the main verb is a fixed label, and 못하다 is the engine that carries tense, politeness, and mood.

No noun+하다 split — that's the point

Short 못 forces noun+하다 action verbs to split (공부하다 → 공부 못 해요). The long form does not. You attach -지 to the whole word and keep 하다 attached, so there's never a question of where the negator goes.

사정이 있어서 회의에 참석하지 못했습니다.

sajeong-i isseoseo hoeuie chamseokaji motaetseumnida

Due to circumstances, I was unable to attend the meeting. (formal)

자료를 제때 제출하지 못했습니다.

jaryoreul jettae jechulhaji motaetseumnida

I wasn't able to submit the materials on time. (formal)

Compare 공부 못 해요 (short, split) with 공부하지 못해요 (long, undivided). This is why -지 못하다 dominates in formal writing: it reads cleanly and never risks the split error.

The parallel: 못 : -지 못하다 :: 안 : -지 않다

The whole negation system lines up in a neat two-by-two. Hold it as a single picture and you never have to memorize four separate rules:

	Short (adverb, pre-verbal, casual)	Long (-지 + auxiliary, formal/written)
Choice / plain fact — "won't / doesn't"	안 가요	가지 않아요
Ability — "can't"	못 가요	가지 못해요

In each row the short member is casual and sits before the verb; the long member is formal, conjugates its own auxiliary (않다 or 못하다), and sidesteps the 공부 안/못 해요 split. Move down a row and you swap "choice" for "ability"; move across and you swap "casual" for "formal." That's the entire system.

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Reach for -지 못하다 in essays, formal apologies and announcements, and emphatic statements of inability — anywhere 못 would feel too clipped. In a written apology, 참석하지 못했습니다 sounds appropriately grave; 못 갔어요 would read as far too casual.

When to use it

Short 못 rules everyday speech; -지 못하다 earns its keep in three places:

Formal / written register — reports, emails, announcements, formal apologies. Paired with 합니다체 (못했습니다), it's the standard way to state an inability formally.
Emphasis — the extra length gives weight, useful when you want the inability to land ("I simply could not…").
Avoiding the split — with noun+하다 verbs, 준비하지 못했어요 is cleaner to build than 준비 못 했어요.

죄송하지만 이번에는 참석하지 못할 것 같습니다.

joesonghajiman ibeoneneun chamseokaji motal geot gatseumnida

I'm sorry, but it looks like I won't be able to attend this time. (formal, hedged)

Common Mistakes

1. Mixing the short and long forms in one predicate. Use either 못 or -지 못하다 — never both.

❌ 오늘은 못 가지 못해요.

Incorrect — that stacks 못 and -지 못하다; say 가지 못해요 (or 못 가요).

✅ 오늘은 가지 못해요.

oneureun gaji motaeyo

I can't go today.

2. Marking tense on the main verb. The past goes on 못하다.

❌ 어제 파티에 갔지 못했어요.

Incorrect — the past belongs to 못하다: 가지 못했어요.

✅ 어제 파티에 가지 못했어요.

eoje patie gaji motaesseoyo

I couldn't go to the party yesterday.

3. Putting a space inside 못하다. As the auxiliary here, 못하다 is written as one word.

❌ 시간이 없어서 준비하지 못 했어요.

Incorrect — the auxiliary is one word: 준비하지 못했어요.

✅ 시간이 없어서 준비하지 못했어요.

sigani eopseoseo junbihaji motaesseoyo

I ran out of time, so I couldn't prepare.

4. Using -지 못하다 for a mere choice. Like short 못, the long form is about inability. If you simply decline, use -지 않다.

❌ 저는 고기를 먹지 못해요.

Misleading if you're a vegetarian by choice — that's 먹지 않아요.

✅ 저는 고기를 먹지 않아요.

jeoneun gogireul meokji anayo

I don't eat meat. (by choice)

Key Takeaways

Build it as stem + -지 + 못하다, then conjugate 못하다 for tense and politeness: 가지 못해요, 오지 못했어요, 참석하지 못했습니다.
Same "can't / unable to" meaning as short 못, but more formal and written, and it never splits noun+하다 verbs (참석하지 못했어요).
Tense lives on 못하다, never on the main verb: 가지 못했어요, not ✗갔지 못해요.
Hold the parallel: 못 : -지 못하다 :: 안 : -지 않다 — short/casual vs long/formal, ability vs choice.
Pronounce 못하다 as [모타다] (aspirated ㅌ), and write it as one word.

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