-지 않다 vs -지 못하다: Chose Not To, or Could Not

The homework

The file would not save. You are empty-handed.

숙제 못 했어요.
sukje mot haesseoyo — I couldn’t do the homework.

못 / -지 못하다 marks a block: time, skill, a jammed printer. You are not confessing that you refused.

Swap the negator.

숙제 안 했어요.
sukje an haesseoyo — I didn’t do the homework.

안 / -지 않다 is the choice, or the simple not. If the printer is the story, 안 했어요 is the failed first line. It sounds like you sat on your hands.

Kimchi at the table

김치 안 먹어요 — you do not eat it. Habit or preference.

김치 못 먹어요 — you cannot: allergy, a rule, a stomach that will not.

Learners borrow 못 to sound polite when they mean 안. Friends hear a medical story you did not mean. Learners also say 안 했어요 for a train they missed. That is 못 탔어요.

Long forms keep the same jobs. 가지 않아요 is the long 안. 가지 못해요 is the long 못. 하다 verbs split: 공부 안 해요, 못 공부해요 is the error the 못 page already flags. Say 공부 못 해요 or 공부하지 못해요.

Softer is not the same word

Koreans do reach for 못 when a no would land heavy: 오늘은 못 가요. That can be kindness. It is still inability-shaped. Do not leave thinking 안 and 못 are style. One is I will not. One is I cannot. If you only remember one failed line, remember 안 했어요 said after a crash ate the file. That seat is 못 했어요. 오늘은 못 마셔요 can be a kind drink-refusal. 오늘은 안 마셔요 is the plain choice. Same glass. Two jobs. 영화를 안 봤어요 is I did not watch it. 영화를 못 봤어요 is the tickets or the time failed you. Do not leave thinking both are fine. English didn’t will try to sell you that lie.