Simply put, 이 and 가 are used to identify the subject of a sentence. One situation where this participle is used is with adjectives:
| Subject | Participle (이/가) |
Adjective | Sentence (Polite Form) |
| 머리 (head) | 가 | 아프다 (sick/painful) |
머리가 아파요. My head aches. |
| 지도 (map) | 가 | 있다 (exist/have) |
지도가 있어요. I have a map (A map exists) |
Looking at the two examples above, the participle "가" identifies the subject. In this case, is is the "head" that hurts, and it is a "map" that the speaker has.
When used with a verb, it emphasizes the fact that the subject was the doer of the action (e.g. It was <subject> that <action>):
| Subject | Participle (이/가) |
Verb | Sentence (Polite Form) |
| 나 (me) | 가 | 주다 (to give) |
내가 줬어. I'm the one that gave it. |
| 강아지 (dog) | 가 | 짖다 (bark) |
강아지가 짖어요. The dog is barking. |
내가 줬어 is directly translated to "I gave", but it emphasizes the fact that it was "I", or the speaker that performed the action. Think of answering the question "Who gave it?".
이 and 가 have the same function, but we use:
| Object / Target | Participle (이/가) |
Example |
| 책 | 이 | 이 책이 좋아요. |
| 휴지 | 가 | 휴지가 필요해요. |
| 티비 (TV) | TV가 | TV가 없어요. |
To summarize, 이/가 are particles that identify the subject of a sentence. Most times, it gives an extra emphasis on the subject. Unlike 은/는, another subject particle, it is used more for questions and does not create a sense of comparison.