The Subject Particle 이/가

이/가 is the subject (nominative) particle: it tags the noun that does the action or undergoes the state — the grammatical subject of the predicate. On paper that sounds like the easiest particle in the language. In practice it is hard, because English speakers reach for it whenever they see an English subject, and Korean does not work that way. 이/가 does not just say "this is the subject"; it says "this is the subject, presented as new information or as the specifically selected answer." Getting that nuance is what separates natural Korean from a word-for-word transfer of English.

The form: 이 after a consonant, 가 after a vowel

Like the topic particle, 이/가 has two shapes chosen by sound. After a noun ending in a consonant (받침), use 이; after a vowel, use 가.

The irregular pronoun contractions you must memorize

Four common pronouns don't just take 가 — their stem changes shape in front of it. There's no deriving these; learn them as fixed forms, because you will say them constantly.

The 네가/니가 point is worth flagging: 네가 and 내가 sound almost identical in modern Seoul speech, so Koreans themselves say 니가 out loud to keep "you" distinct from "I." In writing it's still 네가.

The reframing that matters: 이/가 presents the subject as NEW

Here is where English fights you. In English, the subject slot is neutral — "It's raining," "I'll do it," "Minsu called" all use the same plain subject. Korean's 이/가 is not neutral: it spotlights its noun as freshly introduced or as the one specifically picked out. Think of the English cleft "it is X that…" or heavy stress — that focus is baked right into 가.

This is why 이/가 and topic 은/는 are not interchangeable, even though both can sit on a grammatical subject. 은/는 frames known, agreed-upon information; 이/가 introduces or singles out. Say 비가 와요 and you're reporting the rain as news. Say 비는 와요 and you've implied a contrast — "rain, at least, is coming (but maybe not the snow you wanted)." Same subject, opposite pragmatics. The full comparison lives on 은/는 vs 이/가.

Predicates that strongly pull 이/가

Some predicates almost always want their subject in 이/가 rather than 은/는, because they inherently present or select their subject. Four families to internalize:

Existence — 있다 / 없다. "There is / isn't X" introduces X, so it's new by nature.

Becoming — 되다. What something turns into is the newly-reached result.

Identity-negation — 아니다. "X is not Y" selects X as the thing being denied.

The 이/가 + 좋다/싫다/필요하다 pattern. Korean says likes, dislikes, and needs as "X is good/hateful/necessary to me," and that X takes 이/가 — not 을/를. This surprises English speakers, who expect "I like X" to make X an object.

Honorific subjects use 께서, not 이/가

When the subject is a person you must honor — a grandparent, a professor, a boss — 이/가 is replaced by the honorific subject particle 께서. It's the same grammatical slot, raised in register.

You'll typically pair 께서 with the honorific verb suffix -(으)시-. The details are on the honorific subject 께서; for now, just register that "the 이/가 slot for a respected person becomes 께서."

Casual speech often drops 이/가

In fast, casual conversation, 이/가 is frequently left off when context makes the subject obvious. This is not sloppiness — it's the norm in 반말 and relaxed 해요체, and the dropped particle simply returns whenever you need the focus it carries.

The rule of thumb: drop 이/가 when the subject is short and obvious, but keep it the moment you want to spotlight or contrast the subject. In 누가 그랬어? ("who did it?"), the 가 is doing focus work and won't drop; in 나 배고파 ("I'm hungry"), the subject is so obvious that 내가 would sound heavy. Dropping is covered in full on dropping particles.

Common Mistakes

1. Answering a who/what question with 은/는. The answer to "who came?" identifies a specific doer — that is new-information focus, so it must be 이/가. Using 은/는 sounds like you've changed the subject instead of answering.

2. Making the liked/needed thing an object with 을/를. After 좋다/싫다/필요하다, that thing is the subject, in 이/가.

3. Forgetting the pronoun contraction — saying ×나가 / ×저가. The stem must change: 나→내, 저→제, 누구→누.

4. Using 이/가 for a respected subject instead of 께서. In honorific speech the subject particle is raised too.

Mistake 4 is a matter of register, not raw grammar: 선생님이 is not wrong in casual speech, but in polite contexts where you're already using honorific verb forms, matching the subject particle to 께서 is expected.

Key Takeaways

• 이/가 marks the grammatical subject (doer/experiencer): 이 after a consonant, 가 after a vowel.
• Four contractions are irregular and must be memorized: 내가, 네가 (니가), 제가, 누가.
• 이/가 is not interchangeable with 은/는: it presents the subject as new or specifically selected — the "it is THIS one" reading — which is why wh-answers and "there is…" sentences demand it.
• Existence (있다/없다), 되다, 아니다, and the 이/가 + 좋다/싫다/필요하다 pattern all pull 이/가.
• For a respected subject, 이/가 becomes the honorific 께서.
• The full topic-vs-subject decision is on 은/는 vs 이/가 and the decision tree.