은/는 vs 이/가Topic and subject — which one, and when
Both come out as nothing in English, and they are not interchangeable.
Says what the sentence is ABOUT. Frames, contrasts, and states the general case.
Full entry for 은 ›Says who or what DID it. Identifies, introduces, and answers 'which one?'
Full entry for 이 ›핵심The rule
The usual explanation — "은/는 is the topic, 이/가 is the subject" — is true and almost useless, because an English sentence has no visible topic to compare it to. The distinction that actually predicts which one a Korean speaker will use is old information versus new information.
이/가 introduces. It puts a spotlight on the noun and says this one, this is the one that did it. That is why it is the only possible answer to a 누가 or 뭐가 question, and why a sentence describing something you have just noticed takes it: 비가 와요 — it's raining, said on looking out of the window.
은/는 frames. It takes something both speakers already have in mind and says as for this. That is why self-introductions, general truths and second mentions take it — and why it always carries a whiff of contrast: naming one thing as the frame quietly implies the others are different.
One consequence worth memorising on its own: inside a subordinate clause the subject takes 이/가, never 은/는. 제가 만든 김치 — the kimchi I made. The topic slot belongs to the main sentence, so a clause tucked inside one cannot claim it.
어느 쪽?Which one, when
| Situation | Use | Example |
|---|---|---|
| Answering 누가? / 뭐가? | 이/가 | 누가 왔어요? — 친구가 왔어요. |
| Introducing yourself | 은/는 | 저는 학생이에요. |
| Something you have just noticed | 이/가 | 아, 비가 와요! |
| A general truth | 은/는 | 한국은 사계절이 뚜렷해요. |
| Contrasting two things | 은/는 | 커피는 좋아하는데 차는 안 좋아해요. |
| Subject inside a modifying clause | 이/가 | 제가 만든 김치예요. |
| Second mention of something already named | 은/는 | 옛날에 왕이 있었어요. 그 왕은… |
비교Same sentence, different particle
Both sentences below are correct. That is the point — these are not right-and-wrong pairs, they are two different things to say.
제가 김민준이에요.
I'm Kim Minjun.
Answers "which of you is Kim Minjun?" — 이/가 picks me out of the group.
저는 김민준이에요.
I'm Kim Minjun.
A self-introduction. Nobody was asking; I am setting myself up as the topic.
동생이 학교에 가요.
My brother is going to school.
New information — this is who is going.
동생은 학교에 가요.
My brother goes to school.
As for my brother. Implies someone else in the family does something else.
고양이가 좋아요.
The cat is nice. / I like the cat.
A reaction to this particular cat.
고양이는 좋아요.
Cats are fine (by me).
The general case — and it hints that dogs might be another matter.
자주 하는 실수Common mistakes
✗누가 이거 만들었어요? — 제 친구는 만들었어요.
✓누가 이거 만들었어요? — 제 친구가 만들었어요.
The question asks which person, so the answer has to identify one. 은/는 frames rather than identifies, and the reply lands as a non-answer.
✗저는 만든 김치예요.
✓제가 만든 김치예요.
만든 김치 is a modifying clause and its subject takes 이/가. 저는 tries to make "me" the topic of a sentence whose topic is the kimchi.
사전 예문In the dictionary's own examples
Straight from the 국립국어원 entries, so you can check the rule above against real usage.
은 / 는full entry ›
동생은 부산에 살고 나는 서울에 살고 있다.
My younger sibling lives in Busan, but I live in Seoul.
나는 찌개는 못 끓이는데 볶음밥은 잘 만들어.
I can't cook stew, but I'm good at making fried rice.
오늘은 더웠지만 내일은 비가 온다고 한다.
Today was hot, but they say it will rain tomorrow.
이 / 가full entry ›
오늘 밤은 달이 참 밝다.
The moon is really bright tonight.
나는 신이 있다고 믿는다.
I believe that God exists.
학교 앞에 벚꽃이 예쁘게 피었더라.
The cherry blossoms in front of the school had bloomed beautifully.
관련 문법The full entries
자주 묻는 질문Common questions
Is 은/는 the topic marker and 이/가 the subject marker?
Yes, but that description does not tell you which to use, because English has no visible topic slot to map it onto. The rule that predicts real usage is information status: 이/가 introduces something new or identifies which one, 은/는 frames something already in play and quietly contrasts it with everything else.
Which do I use when introducing myself?
저는. A self-introduction is not answering "which of you is X", it is setting yourself up as what the conversation is now about — that is exactly the topic marker's job. 제가 is the right choice only when someone has asked which person, and you are the answer.
Why is it 제가 and not 저가?
저 + 이/가 contracts to 제가, exactly as 나 + 가 becomes 내가 and 너 + 가 becomes 네가. The plain forms 저가 and 나가 are not used as subjects; the contraction is obligatory.
Can a sentence have both?
Constantly, and it is one of the commonest shapes in the language: 저는 커피가 좋아요. The topic sets the frame — as for me — and the subject marker sits on what is actually doing the being-good. Learners often try to force one marker per sentence; Korean does not work that way.
Example sentences from the 국립국어원 한국어기초사전, used under CC BY-SA 2.0 KR.