Korean attaches small words to nouns to show their job in the sentence. 은/는 and 이/가 both attach to the thing a sentence is about — which is exactly why they overlap, and exactly why textbook explanations can feel circular.
First, the shape rule
Choosing between them starts with the last letter of the noun.
| Particle | After a vowel | After a consonant |
|---|---|---|
| Topic | 는 — 저는 | 은 — 학생은 |
| Subject | 가 — 비가 | 이 — 동생이 |
That part is mechanical. The meaning is the harder half.
은/는 marks the topic
The topic is what the rest of the sentence is about. It often carries a sense of “as for…”, and it is the natural choice for statements about a known person or thing.
저는 학생이에요.
jeoneun haksaeng-ieyo.
I am a student. / As for me, I'm a student.
저 is the speaker, marked as the topic with 는. The rest of the sentence says something about that topic. Notice that the complement 학생 takes 이에요 — that is the polite “to be” ending, not the subject particle, even though it looks similar.
은/는 also signals contrast
This is where the particle earns its keep. If you are contrasting two people or things, 은/는 is doing the work.
저는 매운 음식을 못 먹어요. 친구는 잘 먹어요.
jeoneun maeun eumsigeul mot meogeoyo. chinguneun jal meogeoyo.
I can't eat spicy food. My friend can.
Both people are marked with 는 because the sentence is setting them against each other. Swap in 제가 and the contrast disappears — the sentence starts sounding like an answer to “who can eat it?” rather than a comparison.
이/가 marks the subject — often new information
Use 이/가 when the thing is being introduced, identified, or emphasised as the one doing the action. It answers “who?” or “what?” rather than “what about them?”.
비가 와요.
biga wayo.
It's raining.
Rain is new information here, so it takes 가. 비는 와요 is not wrong grammatically, but it sounds like “as for the rain, it's falling” — usually with an implied contrast, as if you were about to add “…but the snow isn't”.
누가 했어요? — 제가 했어요.
nuga haesseoyo? — jega haesseoyo.
Who did it? — I did.
This is the classic test. The question asks who, so the answer identifies who: 제가. Saying 저는 했어요 would mean “as for me, I did it” — grammatical, but it dodges the question slightly, as though the topic were already you.
A rule that fixes most mistakes: if the noun is already being discussed, or you are contrasting it, reach for 은/는. If you are introducing it, identifying it, or answering “who/what?”, reach for 이/가.
Both in one sentence
They are not alternatives in a sentence — they can appear together, doing different jobs.
저는 동생이 있어요.
jeoneun dongsaengi isseoyo.
I have a younger sibling.
저는 sets the topic: speaking of me. 동생이 is the thing that exists — the subject of 있어요. English “I have” hides this structure; Korean keeps both roles visible.
What about 을/를?
That is the object marker, and it is a separate job: it marks the thing receiving the action.
저는 한국어를 공부해요.
jeoneun hangugeoreul gongbuhaeyo.
I study Korean.
Topic 저는, object 한국어를. No subject particle is needed, because the subject is understood from the topic.
The honest caveat
Real usage is more textured than three rules. Speakers choose these particles for emphasis, rhythm, and nuance, and some verbs and constructions simply prefer one. You will meet sentences that seem to break every rule above — and they will be perfectly natural.
So do not try to solve the pair in one sitting. Learn the five example sentences here as whole chunks, use them until they feel automatic, and let a tutor point out the choices as they come up in your own speech. That is how the distinction actually settles in.
Practice
Choose 은/는 or 이/가, then check the notes below.
- ___ 학생이에요. (I am a student.)
- ___ 와요. (It's raining.)
- 저___ 커피를 좋아해요. (I like coffee.)
- 누___ 했어요? (Who did it?)
Answers: 1. 저는 — topic, a statement about you. 2. 비가 — new information. 3. 는 — topic of the sentence. 4. 누가 — asking who; this form is irregular and always appears as 누가.
Want these explained against your own sentences? That back-and-forth is what a live class is for. See the classes, or start with a free sample lesson.