이/가 아니다: How to Say Something Is Not

Korean does not negate 이다 the way it negates everything else. There is no 안 이다. Instead there is a completely separate word: 아니다.

That is the first thing to know. The second is what it does to the particle in front of it — which is where the real mistakes happen.

The particle changes

This is the rule that catches people.

저는 학생이에요. — I’m a student.
저는 학생이 아니에요. — I’m not a student.

Look at what happened to 학생. In the positive sentence, 이다 is glued straight onto it. In the negative, the noun separates and takes 이/가.

The same consonant/vowel split applies:

학생 (consonant)  →  학생이 아니에요
가수 (vowel)      →  가수가 아니에요

Learners reach for 을/를 here because English feels like the noun is an object. It is not. In Korean, 아니다 is saying “the thing called X — that is not it,” and X is the subject of that judgment.

저는 학생을 아니에요.   ❌
저는 학생이 아니에요.   ✅

Why 안 does not work

안 and -지 않다 handle ordinary negation — 안 가요, 좋지 않아요. But 이다 is outside that system.

저는 학생 안 이에요.   ❌  not Korean
저는 학생이 아니에요.  ✅

There is no deeper reason to discover. 이다 and 아니다 are a pair that has existed as a pair, the way English has is and is not rather than not-is.

The forms

Using 은/는 instead, on purpose

Swapping the particle is grammatical and changes the meaning:

학생이 아니에요 — I’m not a student. (neutral)
학생은 아니에요 — I’m not a student. (…but I might be something adjacent)

That is 은/는 vs 이/가 smuggling in a contrast, exactly as it always does. Useful when you mean it — misleading when you do not. Default to 이/가.

아니에요 on its own

Detached from a noun, 아니에요 is one of the most common words in spoken Korean.

• 아니에요. — No, that’s not it.
• A: 감사합니다! B: 아니에요. — Thanks! / Not at all.
• A: 죄송해요. B: 아니에요, 괜찮아요. — Sorry. / It’s fine, really.

That second use is worth copying. Where English says “you’re welcome,” Korean often deflects the thanks instead. 아니에요 does that deflecting, and it sounds warmer than 천만에요, which most learners are taught first and which native speakers rarely say.

Do not confuse it with 아니요

A: 학생이에요? — Are you a student?
B: 아니요, 학생이 아니에요. — No, I’m not a student.

Both in one sentence, doing different work. Once you see them side by side the difference is easy to hold on to.