-지 못하다 is the long/formal form expressing inability. More emphatic than 못, commonly used in formal speech and writing.
Formal inability - Written and polite contexts
Stronger emphasis - More weight than short 못
Verbs only - Cannot use with adjectives
I couldn''t go because I didn''t have time.
Conjugate 못하다 for tense: 못해요 (present), 못했어요 (past).
Only for verbs, NOT adjectives
- ✅ 가지 못하다
- ❌ 예쁘지 못하다 (use 않다 instead)
-지 않다 vs -지 못하다
- 않다 = choice/general negation
- 못하다 = inability
I couldn't sleep yesterday.
I cannot speak Korean.
I couldn't keep my promise.
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