은/는 vs 이/가 — Topic and Subject, Simply

은/는 marks the topic — "as for this…" — and 이/가 marks the subject — "this one (and not another) does it." Use 은/는 for what the conversation is already about, or to contrast. Use 이/가 for new information, for the answer to "who?" or "what?", and in a few fixed patterns. Everyone mixes them up at first — even advanced learners — so here is the short version.

1. Which form? Look at the last sound

Both particles have two shapes, and the choice depends only on whether the noun ends in a consonant (has a final 받침) or a vowel.

A few common words change shape with 가: 나 + 가 → 내가, 저 + 가 → 제가, 너 + 가 → 네가, 누구 + 가 → 누가.

2. 은/는 — "as for…"

Think of 은/는 as setting the stage: this is what I am going to talk about.

• Introducing yourself: 저는 마리아예요. — "As for me, I'm Maria."
• General facts: 고래는 포유류예요. — "Whales are mammals."
• Something already known: Once a person or thing is in the conversation, it usually becomes the topic.
• Contrast: 저는 커피는 좋아해요. 그런데 차는 안 좋아해요. — "Coffee, I like. Tea, I don't." Here 는 quietly says as opposed to something else.

3. 이/가 — "this one is the one"

이/가 points at the doer or the thing being described, often as new information.

• Answering who / what: 누가 왔어요? — 민수가 왔어요. ("Who came?" — "Minsu came.") Question words like 누가 and 뭐가 take 이/가, and so does the answer.
• Introducing something new: 옛날에 한 소녀가 살았어요. 그 소녀는 꽃을 좋아했어요. — the girl appears with 가, then becomes the topic with 는.
• Noticing something right now: 어, 비가 와요! — "Oh, it's raining!"

4. Patterns that take 이/가

Some expressions almost always use 이/가 for the thing in question.

The last row matters: when a clause describes a noun (제가 만든 → "that I made"), its subject takes 이/가, not 은/는.

5. Both in one sentence

Korean happily uses both at once: the topic sets the stage, and the subject tells what is true about it.

• 저는 동생이 있어요. — "As for me, I have a younger sibling."
• 코끼리는 코가 길어요. — "As for elephants, their noses are long."
• 서울은 사람이 많아요. — "As for Seoul, there are many people."

Read them as topic → subject → description, and they stop looking strange.

6. Don't worry too much

Swapping them usually won't stop people from understanding you. 저가 학생이에요 sounds odd (it should be 제가), and 저는 왔어요 to answer "Who came?" sounds like you are contrasting yourself with someone else — but listeners will still get the meaning. The feel for 은/는 and 이/가 comes from hearing many short sentences, so read and build simple ones until the patterns feel natural. Picture Sentences lets you build sentences piece by piece with particles like -가 and -를.