Use 이/가 (i/ga) when the noun is new information, the answer to “who” or “what,” or the one thing being picked out. Use 은/는 (eun/neun) when the noun is a topic the listener already has in mind, or when you are contrasting it with something else. English signals the same difference with stress and articles, not particles.
Both pairs change shape depending on whether the noun ends in a consonant or a vowel. This part is mechanical, so get it out of the way before worrying about meaning.
| Marker | After a consonant | After a vowel |
|---|---|---|
| Topic | 책은 (chaegeun), the book | 저는 (jeoneun), I |
| Subject | 책이 (chaegi), the book | 친구가 (chinguga), a friend |
Three common words change form with 가. 저 (jeo), the polite I, becomes 제가 (jega). 나 (na), the casual I, becomes 내가 (naega). 누구 (nugu), who, becomes 누가 (nuga). “저가” and “누구가” are mistakes English speakers make constantly, because nothing in English prepares you for a pronoun that changes shape before a particle.
Compare “Minsu came” said flatly with “Minsu came” stressed, as an answer to “Who came?” The stressed version is roughly what 이/가 does. Now compare “As for Minsu, he came,” which sets Minsu up as the thing you are talking about and hints that others may not have. That is the job of 은/는.
| Korean | Closest English feel |
|---|---|
| 누가 왔어요? (nuga wasseoyo?) | Who came? |
| 민수가 왔어요. (minsuga wasseoyo.) | Minsu came. (that is the answer) |
| 민수는 왔어요. (minsuneun wasseoyo.) | Minsu came, at least. (others didn’t?) |
If someone asks who came and you answer with 민수는, you have not answered the question. You have changed the subject to Minsu and implied a contrast nobody asked for. Native listeners will wait for the “but.”
Question words that act as the subject never take 은/는. It is always 누가 (nuga), who; 뭐가 (mwoga), what; 어디가 (eodiga), where; and 언제가 (eonjega), when, as in 언제가 좋아요? (eonjega joayo?), when is good for you? The answer slot takes 이/가 too, because it supplies the new piece of information.
That last one is a classic English speaker slip. You have said 저는 (jeoneun) in every self-introduction, so 저는 했어요 comes out on autopilot. Here it sounds like “I, for my part, did it,” which dodges the question. 제가 is the answer.
Korean folk tales show this pattern clearly. 옛날에 호랑이가 살았어요 (yennare horangiga sarasseoyo), once upon a time there lived a tiger. 호랑이는 배가 고팠어요 (horangineun baega gopasseoyo), the tiger was hungry. The tiger enters the story with 가, then becomes the topic with 는. It mirrors English “a tiger” turning into “the tiger,” which is a useful anchor even though Korean has no articles.
Notice 배가 (baega) in the second sentence: the tiger is the topic, and the stomach is the subject of being hungry. Korean sentences often carry both a topic and a subject at once, and English speakers tend to force one of them out.
Several everyday patterns put the person in 은/는 and the thing in 이/가. English turns that thing into an object, so learners reach for the object marker 을/를 (eul/reul) by mistake.
| English | Korean | Common mistake |
|---|---|---|
| I have a car. | 저는 차가 있어요. (jeoneun chaga isseoyo.) | 저는 차를 있어요 |
| I like coffee. | 저는 커피가 좋아요. (jeoneun keopiga joayo.) | 저는 커피를 좋아요 |
| I need time. | 저는 시간이 필요해요. (jeoneun sigani piryohaeyo.) | 저는 시간을 필요해요 |
| I am not a student. | 저는 학생이 아니에요. (jeoneun haksaengi anieyo.) | 저는 학생은 아니에요 (only if contrasting) |
One wrinkle: 좋아해요 (joahaeyo), the action verb for like, does take an object, so 저는 커피를 좋아해요 (jeoneun keopireul joahaeyo) is correct. The trap is mixing the two, putting 를 on the noun and then using 좋아요.
은/는 can replace other particles to set up a contrast. 고기는 먹어요. 생선은 안 먹어요. (gogineun meogeoyo. saengseoneun an meogeoyo.) I eat meat. Fish, I don’t eat. Here meat and fish are objects, but 은/는 replaces 을/를 to put them side by side.
This is why 은/는 shows up so often in negative sentences. 오늘은 안 돼요 (oneureun an dwaeyo) means today doesn’t work, and the 은 quietly implies another day might. Said with 오늘이 (oneuri), it would sound like you are naming today as the problem day, which is a different message.
When a clause describes a noun, its subject takes 이/가, not 은/는. 제가 산 책 (jega san chaek) means the book I bought. 저는 산 책 sounds broken. English speakers who have drilled 저는 as the only way to say I make this mistake in nearly every relative clause.
When you report something you just noticed, the whole event is new, so the subject takes 이/가. 비가 와요 (biga wayo), it is raining. 버스가 와요 (beoseuga wayo), the bus is coming. 비는 와요 (bineun wayo) would mean something like “well, it is raining, but,” as if you were conceding a point.
| Situation | Use | Example |
|---|---|---|
| Introducing yourself | 은/는 | 저는 마이클이에요. (jeoneun maikeurieyo.) |
| Answering who or what | 이/가 | 제가 할게요. (jega halgeyo.) I’ll do it. |
| Question word as subject | 이/가 | 누가 와요? (nuga wayo?) |
| Contrasting two things | 은/는 | 저는 좋아요. (jeoneun joayo.) As for me, I’m fine with it. |
| Something you just noticed | 이/가 | 문이 열렸어요. (muni yeollyeosseoyo.) The door opened. |
| Inside a describing clause | 이/가 | 친구가 만든 음식 (chinguga mandeun eumsik) |
The fastest way to make this automatic is to answer real questions out loud. When someone asks “누가?” or “뭐가?”, your mouth has to produce 이/가 in under a second, which a worksheet never forces. A daily spoken session with a tutor like Polly in PollyStop, where you answer and get corrected on the spot, builds that reflex.
No. 은/는 marks the topic, which can be the subject, the object, a time, or a place. In 고기는 안 먹어요 (gogineun an meogeoyo), meat is the topic but grammatically the object of eat.
Because in conversation you are usually the established topic. 저는 sets you as what the sentence is about. Switch to 제가 when you are the answer to who, or when you are picking yourself out from a group.
In casual speech Koreans often drop particles, especially 이/가 and 을/를. It is safer for learners to keep them, because a dropped particle is natural but a wrong one changes the meaning.
They are equally polite. Both use the humble 저. The difference is information structure, not politeness: 제가 answers or singles out, 저는 sets a topic or contrasts.
