Part of the Korean Whodunit grammar series · Korean reviewed by native speakers
Korean has two ways to negate an action, and they are not interchangeable. 안 says you chose not to; 못 says you couldn’t. That is the difference between refusal and inability — and in a statement, it quietly exposes what a person actually meant.
Put 안 directly before the verb to say someone doesn’t or won’t do something, of their own will. It carries no sense of being unable; it is a decision.
I don’t drink coffee — I simply choose not to. (안 + verb)
That night I didn’t go out — by choice. (안 나가다 = chose not to go)
The longer form ~지 않다 means the same thing: 마시지 않아요 = 안 마셔요. Both negate the will, not the ability.
Put 못 before the verb to say someone was unable to do something — blocked by circumstance, a rule, or a physical limit. It is not a choice; it is a wall.
I can’t drink coffee — an allergy or condition stops me. (못 + verb)
That night I couldn’t go out — something prevented me. (못 나가다 = was unable to leave)
A suspect who first says 안 나갔어요 (“I chose not to go out”) and later says 못 나갔어요 (“I couldn’t go out”) has told two different stories. One claims free will; the other claims an obstacle — and an obstacle can be checked. Swapping 안 for 못 mid-interview is a motive being rewritten in real time.
못 attaches to action verbs, not descriptive ones. You can be 안 좋아요 (“not good”), but never 못 좋아요. Ability-negation only makes sense for things you do, not things you are.
Use 안 with adjectives; 못 only negates actions.
Negation is never just grammar — it is a claim about why. In our cases, the gap between “I wouldn’t” and “I couldn’t” is often where the lie lives.
In Korean Whodunit, a suspect’s choice of 안 or 못 can betray whether they’re hiding a decision or inventing an excuse. Read the statements and watch the negation. Free, no sign-up.
Browse the Cases →