은/는 vs 이/가 — The Difference Nobody Explains Properly

Every Korean textbook tells you the same thing: 은/는 marks the topic, 이/가 marks the subject. Then it moves on, and you spend the next six months guessing.

The problem is that "topic" and "subject" are grammar words borrowed from linguistics. They describe the particles accurately, but they don't tell you which one to say. Here is a version you can actually use.

The form is the easy part

Pick based on whether the preceding word ends in a consonant or a vowel.

책은 (book), 커피는 (coffee), 책이, 커피가. That's the whole mechanical rule. Everything below is about which pair you reach for.

The one idea: old information vs new information

이/가 introduces. 은/는 comments on something already introduced.

That's it. If the listener doesn't yet know what you're talking about, you need 이/가. Once it's on the table, you switch to 은/는.

Watch it happen inside a single exchange:

• 누가 왔어요? — Who came?
• 친구가 왔어요. — A friend came. (new information — 가)
• 그 친구는 미국 사람이에요. — That friend is American. (now established — 는)

Using the wrong one isn't a grammar error so much as a tone error. 친구는 왔어요 sounds like you're contrasting your friend with somebody else who didn't come.

Four places where 이/가 is the only option

These are worth memorizing outright, because they come up constantly.

1. Answering "who" or "what"

The answer to a question word takes 이/가, always.

• 뭐가 문제예요? → 약속이 문제예요.
• 누가 했어요? → 제가 했어요.

Saying 제는 했어요 is wrong. (Also note 제가, not 저가 — 저 + 가 contracts.)

2. Describing something you just noticed

• 비가 와요! — It's raining!
• 버스가 왔어요! — The bus is here!

You're reporting fresh news, so it's 이/가.

3. Inside a relative clause

The subject of a modifying clause takes 이/가, even if you'd use 은/는 in a standalone sentence.

• 제가 만든 김치 — the kimchi I made
• 날씨가 좋은 날 — a day when the weather is nice

제는 만든 김치 is simply ungrammatical.

4. With 있다 / 없다 / 되다 and adjectives of state

• 시간이 없어요. — I don't have time.
• 한국어가 어려워요. — Korean is hard.

You can say 한국어는 어려워요, but it changes the meaning to "Korean, as opposed to other languages, is hard." Which brings us to the useful part.

은/는 as a contrast marker

This is the piece most learners never get told. 은/는 quietly implies "…as for this one, unlike others." Native speakers use it on purpose.

So when someone asks how your Korean is going and you answer 말하기는 괜찮아요, you've said "speaking is fine" and implied "…my listening is not." Sometimes that's exactly what you meant. Sometimes you've accidentally insulted the food.

A test you can run in your head

Ask yourself: could I put "as for" in front of it in English and still mean the same thing?

• As for me, I'm going home. → 저는 집에 가요. ✅
• Who's going home? — As for me, I'm going. ❌ → 제가 가요.

It's not a perfect rule, but it's right often enough to get you through a conversation, and conversations are where this actually gets learned.

Practice these five

Cover the right column and try each one.

That last one has both particles doing separate jobs in one sentence — 오늘은 sets up the topic ("today, unlike other days"), and 시간이 is the subject of 없어요. Once that sentence feels natural, you've got it.

The part that isn't optional

You will not learn this from a table. You learn it by saying it wrong, having someone correct you, and noticing the pattern the fourth or fifth time. The rules above just make the corrections land faster.