이/가: The Subject Particle That Marks New Information

Textbooks say 이/가 is “the subject particle,” which is true and tells you almost nothing about when to use it.

Here is the version that actually helps: 이/가 points at something and presents it as news.

The form

Same consonant/vowel split as every Korean particle:

Ends in a consonant → 이
Ends in a vowel → 가

사람  →  사람이
날씨  →  날씨가

Three pronouns contract, and you should learn them as words rather than deriving them:

What it actually does

The clearest demonstration is answering a question.

누가 왔어요? — Who came?
민수가 왔어요. ✅ — Minsu came.

The question asks for information you do not have — which person. New information takes 가.

Now try answering with 는:

민수는 왔어요. — Minsu, at least, came.

Still grammatical. But it no longer answers the question — it has become a comparison, implying someone else did not come. That is 은/는 vs 이/가 doing its job, and it is the wrong job here.

Flip it around and 는 becomes correct:

민수 뭐 해요? — What’s Minsu up to?
민수는 자고 있어요. ✅ — Minsu’s sleeping.

Minsu is already in the conversation. He is not the news. The sleeping is.

Weather, bodies, and noticing things

These take 이/가, and they are fixed enough to memorise as phrases:

• 날씨가 좋아요 — The weather’s nice.
• 배가 고파요 — I’m hungry.
• 머리가 아파요 — I have a headache.
• 시간이 없어요 — I don’t have time.

The pattern underneath: all of these are things you are noticing right now. 배고프다 literally says the belly is hungry — the belly is the subject, and it is what the sentence is presenting.

Switch to 날씨는 좋아요 and you have said “the weather, at least, is nice” — implying something else about the day is not. Sometimes that is what you want. Usually it is not.

The one that surprises people

A few adjectives take 이/가 where English uses an object:

• 커피가 좋아요 — I like coffee.
• 돈이 필요해요 — I need money.
• 한국어가 어려워요 — Korean is hard.

In Korean these say coffee is good (to me), money is needed. The thing you would call the object in English is the grammatical subject here. Do not try to force English structure onto them — learn them as they are.

Note 저는 커피를 좋아해요 also exists, with 좋아하다 rather than 좋다. Different verb, different particle.

A rule you can use today

1. Answering “who?” or “what?” → 이/가
2. Weather, body, time, sudden noticing → 이/가
3. Something already being discussed → 은/는 vs 이/가
4. Comparing two things → 은/는 vs 이/가 on both

You will still get it wrong sometimes. Everyone does, for years, and it almost never blocks understanding. But once you hear that 이/가 is pointing and 은/는 is framing, the choice stops feeling random.