This is the question every Korean learner hits, usually in week three, and the standard answer — "은/는 is the topic marker, 이/가 is the subject marker" — helps almost nobody. English has no topic marker, so the label explains nothing.
Here's a way in that's more useful.
Start with what they do, not what they're called
이/가 points at something. It picks one thing out and says: this one, specifically.
은/는 sets the frame. It says: as for this thing, here's what I want to say about it.
That difference in feel drives most of the usage.
(Which form you use is just sound. 이 and 은 go after a consonant, 가 and 는 after a vowel. That part is mechanical.)
The clearest case: answering a question
Someone asks 누가 왔어요? — who came?
You answer 에마가 왔어요. Emma came.
You use 가 because the question is which person, and you're pointing at the answer. Using 는 here would sound off.
Now someone asks 에마는 뭐 해요? — what's Emma doing?
You answer 에마는 공부해요. Emma is studying.
Here 는 is right, because Emma isn't the new information. She's the frame. The new part is what she's doing.
Rule of thumb: 이/가 marks new information, 은/는 marks information already on the table.
The second big use: contrast
은/는 quietly implies a comparison. This is where learners feel something is odd without knowing why.
저는 커피 좋아해요. — I like coffee. (…others might not. Or: as for me, specifically.)
If someone says 김치는 좋아해요, a Korean ear hears an unfinished thought — I like kimchi, implying there's something else they don't like. It's a small implication, but it's there.
This is why 는 can sound slightly defensive or pointed if you use it where 가 belongs.
Introducing vs continuing
Watch what happens across two sentences.
친구가 왔어요. 그 친구는 미국 사람이에요. A friend came. That friend is American.
First mention uses 가 — new person, pointed at. Second mention uses 는 — now established, so it becomes the frame for the next statement.
This pattern shows up constantly in stories and conversation. New thing enters with 이/가, then continues with 은/는.
Why explanations only get you so far
You can understand everything above and still pick wrong in conversation. That's normal, and it's not a sign you've misunderstood.
Particles operate below the level of conscious rules for native speakers. They're chosen by feel, from thousands of hours of exposure. You're building that same feel, and rules can only point you in the direction.
What helps:
Notice, don't drill. When you read or listen, pay attention to which particle appears and ask why. Ten noticed examples beat a hundred fill-in-the-blank exercises.
Learn them inside phrases. 저는 ___예요 and 제 이름은 ___예요 come as units. Learn the unit and the particle comes free.
Accept a long tail. Advanced learners still occasionally pick the less natural one. It rarely blocks communication — people will understand you either way.
The short version
- Answering which one → 이/가
- Talking about something already known → 은/는
- Implying a contrast → 은/는
- First mention → 이/가, after that → 은/는
These cover most everyday cases. The exceptions come later, and by then you'll have enough exposure that they'll feel less arbitrary.
K-PATTO teaches particles the way you'll actually meet them — inside real sentences from webtoon scenes, with audio, rather than as isolated grammar rules.