은/는 vs 이/가: one question instead of ten rules

「저는 학생이에요」 and 「제가 학생이에요」 are both correct sentences that mean different things. This is the question Korean learners ask most, and most answers hand you a list of ten rules. The list does not help when you are actually writing a sentence.

One question works better than the list.

Am I bringing this up for the first time, or have we been talking about it?

New information takes 이/가. Old information takes 은/는

The first two sentences of any Korean folk tale show this more clearly than any explanation.

옛날에 한 할아버지가 살았습니다.
그 할아버지는 매일 산에 나무를 하러 갔습니다.

In the first sentence the old man appears for the first time — 이/가. By the second sentence he is someone we both know about — 은/는. Swap them and the first sentence sounds wrong, because it treats a stranger as though you already knew him.

This is why introducing yourself is 「저는 학생이에요」. You are not new information — you are standing right there. 「제가 학생이에요」 is closer to 「I am the student」, as an answer to the question of which person is the student. Outside that context it sounds odd.

ParticlesN이/가Subject marker pointing out who or what performs the action. Often introduces new information.Start with this one. The examples are all first-mention sentences, which is the clearest caseWrite your own sentence with this →Form, examples and what to watch out for

The question decides the answer

Question words make the rule visible.

누가 왔어요? — 제임스가 왔어요.
제임스는 왔어요? — 네, 제임스는 왔어요.

「누가」 asks about something unknown, so it takes 이/가, and the answer fills that same slot, so it takes 이/가 too. 「제임스는 왔어요?」 is what you ask when James is already the topic and you only want to know whether he showed up.

은/는 is closer to 「as for」

If you read 은/는 as 「as for」, contrast falls out on its own.

커피는 좋아하는데 우유는 싫어해요.As for coffee I like it, but as for milk I do not.

Two things are being weighed against each other, so both take 은/는. Using 이/가 here breaks the comparison.

ParticlesN은/는Topic marker used to introduce what you are talking about or to draw a contrast with something else.Worth reading the watch-out section here specifically — the implied contrast is the part that causes real misunderstandingsWrite your own sentence with this →Form, examples and what to watch out for

Inside a modifying clause, only 이/가 is possible

Everything above is about nuance. This part is a hard rule. The subject of a clause that modifies a noun must take 이/가.

제가 만든 음식 (correct)
저는 만든 음식 (not possible)

「제가 좋아하는 노래」, 「비가 오는 날」, 「사람이 많은 곳」 — all the same slot. Learners hit this constantly once sentences get longer, not because the rule is hard but because the habit of starting sentences with 「저는」 follows them into the clause.

Changes in Parts of Speech관형형 -(으)ㄴ/-는/-(으)ㄹ NChanges verbs and adjectives into forms that attach in front of nouns to modify them.This is the structure the rule above lives inside. If modifying clauses are still new, read this firstWrite your own sentence with this →Form, examples and what to watch out for

The short version

First mention · question words and their answers · subject inside a modifying clause → 이/가
Already the topic · contrast · anywhere 「as for」 fits → 은/는
If you do not want to imply something unsaid, avoid 은/는

Knowing the rules does not make the right particle come out when you are speaking. This is a case where the gap between recognising and producing is unusually wide, so the fastest way through is to write your own sentences and have them checked.

Telling 이/가 and 은/는 apart — two lessonsBuilt around asking 「is this new, or are we already talking about it」 rather than memorising a listOpen it → All 20 Korean particles, comparedSee 이/가 and 은/는 next to 을/를, 도, 만 and the rest, with the form and watch-outs for eachOpen it →