The questions gathered here are the ones Korean learners actually ask most often. They make more sense when you approach them by asking 'in what situation is this used' rather than by memorizing rules.
This is the question Korean learners ask most. It doesn't reduce to two or three rules — it depends on what the sentence is trying to say.
'이/가' is used to pin down brand-new information or exactly 'who did it.' '은/는' is used to raise something already known as the topic, or to contrast it with something else.
The easiest way to feel it is through answers. 'Who came?' (누가 왔어요?) is answered with '민수가 왔어요' (Minsu came) — since the question asks 'who,' you use '이/가.' But if Minsu is already the topic, as in '민수는 뭐 해요?' (What is Minsu doing?), you use '은/는.'
| Situation | Particle used | Example |
|---|---|---|
| Something mentioned for the first time | 이/가 | 옛날에 한 할머니가 살았어요 (Once there lived an old woman) |
| Something already mentioned (the topic) | 은/는 | 그 할머니는 마음이 착했어요 (That grandmother was kind-hearted) |
| Answering 'who' | 이/가 | 누가 했어요? — 제가 했어요 (Who did it? — I did.) |
| Contrasting two things | 은/는 | 형은 키가 크고 동생은 작아요 (The older brother is tall and the younger one is short) |
| Subject inside a subordinate clause | 이/가 | 비가 와서 못 갔어요 (It rained, so I couldn't go) |
This is also why self-introductions start with '저는 김민수입니다' (I'm Kim Minsu) — because you're raising 'me' as the topic. '제가 김민수입니다' would instead mean picking yourself out as that person among several people.
Because in everyday conversation, the meaning still comes across even without them. '밥 먹었어?' (Did you eat?) is '밥을 먹었어?' with the '을' dropped.
Particles only get dropped when context already makes the role clear. '을/를' and '이/가' are dropped often, but particles that determine meaning — like '에게 (to)·에서 (at/from)·으로 (with/toward)' — change the meaning if you drop them, so they're kept.
In TOPIK writing, though, don't drop them. Q51–54 are graded against written-style standards, so you need to write complete sentences with their particles intact.
Getting just '해요체' (the -요 speech level) solid handles most situations. It's the safest register to use with strangers.
'합니다체 (-습니다)' is used in formal settings — presentations, news broadcasts, the military, official documents. TOPIK Writing Q51–54 also fall into this register.
반말 (casual speech, -아/어) is used only with close friends or people younger than you. Using it with someone you just met can offend them, so it's safer not to use it until the other person suggests '말 놓자' (let's drop the honorifics) first.
| Register | Example | Where it's used |
|---|---|---|
| 합니다체 | 감사합니다 (Thank you) / 하겠습니다 (I will do it) | Presentations · official documents · TOPIK writing |
| 해요체 | 감사해요 (Thank you) / 할게요 (I'll do it) | Everyday polite speech — the safest choice |
| 반말 | 고마워 (Thanks) / 할게 (I'll do it) | Close friends · people younger than you |
Honorifics come in two separate kinds — raising the listener (speech level) and raising the sentence's subject (-시-). As in '사장님이 오셨어요' (The boss has arrived), '-시-' raises the person the sentence is about.
The most important difference is what can follow. A command or suggestion can't follow '-아/어서.'
'늦어서 미안해요' (Sorry for being late) works, but '늦어서 빨리 가세요' (Because I'm late, please hurry) is wrong. You'd have to say '늦었으니까 빨리 가세요' instead.
One more thing: greetings, thanks, and apologies conventionally use '-아/어서' — '와 주셔서 감사합니다' (Thank you for coming) sounds natural, while '와 주셨으니까 감사합니다' sounds off.
| -아/어서 | -(으)니까 | |
|---|---|---|
| Can be followed by a command/suggestion | No | Yes |
| Combines with past tense '-았/었-' | No (늦어서 ✓ / 늦었어서 ✗) | Yes (늦었으니까) |
| Thanks/apology greetings | Natural | Awkward |
The test is whether the first action carries over into the second.
'손을 씻고 밥을 먹었어요' (I washed my hands and ate) just means the two actions happened one after the other — the washed hands aren't directly linked to the eating.
'의자에 앉아서 책을 읽었어요' (I sat in the chair and read a book) means the reading happened while staying seated — the result of the first action becomes the condition for the second.
That's why '집에 가서 잤어요' (I went home and slept) works, but '집에 가고 잤어요' sounds off — because you're sleeping while in the state of having gone there.
'-았/었-' marks something finished; '-고 있었-' marks something that was in progress at that time.
'어제 책을 읽었어요' (I read a book yesterday) means I finished reading or the act of reading ended, while '어제 책을 읽고 있었어요' (I was reading a book yesterday) means I was in the middle of reading at some point.
'-고 있다' can also mark a state rather than an ongoing action. '안경을 쓰고 있어요' (I'm wearing glasses) doesn't mean the act of putting them on right now — it means the state of having them on. Verbs for wearing or holding — 입다 (wear clothes)·신다 (wear shoes)·쓰다 (wear on the head/face)·들다 (hold/carry) — work this way.
The passive (피동) means 'having something done to you'; the causative (사동) means 'making someone do something.'
'문이 열렸다' (The door opened/was opened) means the door had the opening done to it — passive. '내가 문을 열었다' (I opened the door) means I did it myself. '아이에게 옷을 입혔다' (I dressed the child) means I made the child put on clothes — causative.
It's confusing because the forms overlap. '보이다' works as both '보인다' (is seen — passive) and '보여 준다' (shows — causative). Rather than memorizing by form, judge from the sentence who's actually the doer of the action.
In TOPIK, the passive shows up a lot in reading passages. '~로 알려져 있다 (is known as...) / ~라고 불린다 (is called...) / ~에 의해 ~되었다 (was... by...)' are basic sentence patterns in explanatory writing, so knowing them speeds up your reading.
Because the form changes with the sentence type. It's faster to organize it into a table and memorize the whole set.
In real conversation, you hear the contracted forms even more often — '간다고 해요' (they say [someone] is going) contracts to '간대요,' and '가냐고 해요' (they ask if [someone] is going) contracts to '가냬요.' These contractions come up a lot in listening.
| Sentence type | Form | Example |
|---|---|---|
| Statement (verb) | -ㄴ/는다고 하다 | 간다고 했어요 (They said [someone] is going) |
| Statement (adjective) | -다고 하다 | 춥다고 했어요 (They said it's cold) |
| Question | -냐고 하다 | 가냐고 물었어요 (They asked if [someone] is going) |
| Command | -(으)라고 하다 | 가라고 했어요 (They told [someone] to go) |
| Suggestion | -자고 하다 | 가자고 했어요 (They suggested going) |