이/가
subject marker
Marks who or what performs the action. Which of the two forms you use depends on one thing only: whether the noun ends in a consonant.
Build it
Pick a noun
When to use it
이/가 points at the doer. In 고양이가 자요, the cat is the one sleeping, and the particle is what tells you so — Korean word order alone will not.
Beyond that basic job, 이/가 carries a second signal that English has no equivalent for: it presents the noun as new or selected information. Answer the question 누가 왔어요? and the answer must take 이/가, because the whole point of your reply is to identify which person. This is the difference that trips up learners, and it is why 이/가 and 은/는 are not interchangeable even though both can sit on a subject.
It is also required, not optional, after certain predicates: 있다, 없다, 되다, 아니다, and adjectives describing a state all take a 이/가 subject.
How to attach it
| Noun type | Form | Example |
|---|---|---|
| Ends in a consonant | 이 | 학생이 |
| Ends in a vowel | 가 | 친구가 |
| 나 (I, casual) | 내가 | 내가 — not 나가 |
| 저 (I, polite) | 제가 | 제가 — not 저가 |
| 너 (you, casual) | 네가 | 네가 — spoken as 니가 |
| 누구 (who) | 누가 | 누가 — not 누구가 |
| Honorific subject | 께서 | 선생님께서 |
In use
동생이 지금 자요.
My younger sibling is sleeping right now.
친구가 한국에서 왔어요.
A friend came from Korea.
시간이 없어요.
There is no time.
누가 이 책을 읽었어요?
Who read this book?
제가 하겠습니다.
I will do it.
할아버지께서 신문을 보세요.
Grandfather is reading the newspaper.
Compared with
은/는
은/는 marks the topic — what the sentence is about, or what is being contrasted. 이/가 marks the subject and presents it as new. Both can attach to the same noun, and swapping them changes what the listener hears as the point of the sentence.
제 이름은 마이클이에요. (introducing myself: the topic is my name) / 마이클이 제 이름이에요. (of the names available, Michael is mine)
Answering a question
When your reply supplies the missing piece of information, that piece takes 이/가. Using 은/는 there sounds like you are changing the subject.
누가 왔어요? → 마이클이 왔어요. (correct) / 마이클은 왔어요. (as for Michael, he did come — but what about the others?)
께서
The honorific form of 이/가, used when the subject is someone you are showing respect to. The verb usually takes -(으)시- to match.
선생님께서 오셨어요. / 친구가 왔어요.
Watch out
나가 할게요.
내가 할게요.
나 and 저 change shape before 가. There is no 나가 or 저가 — only 내가 and 제가. This is the most frequent beginner error in speech.
누구가 왔어요?
누가 왔어요?
누구 contracts to 누 before 가. The full form survives elsewhere, as in 누구를 or 누구예요.
친구이 왔어요.
친구가 왔어요.
Choose by the last letter of the noun, not by meaning or by how the word feels. 친구 ends in a vowel, so it takes 가.
Next
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