이/가

RuleNoun + i/ga: marks the grammatical subject (nominative). After a consonant use i; after a vowel use ga.

Curiosity

Answering "who came?", you say chingu-ga wasseoyo ("a friend came"). Why chingu-ga and not chingu-neun?

Intuition

i/ga points at a freshly introduced subject: "this one, right here!" Use it when delivering new information the listener did not yet know.

Visualization

See which form attaches to a consonant-final noun (chaek) versus a vowel-final one (chingu): chaek → chaek-i, chingu → chingu-ga.

Rolesubject (nominative)

ends in a consonant책book

ends in a vowel친구friend

Essence

i/ga = subject as new/focused information; eun/neun = an already-known topic. "Long ago a king (i/ga) lived. The king (eun/neun)…": something first appears with i/ga, then shifts to eun/neun when mentioned again.

Examples

친구가 와요.

A friend is coming.

책이 있어요.

There is a book.

날씨가 좋아요.

The weather is nice.

Mini-quiz

"Who came?" — "chingu__ wasseoyo." (A friend came) What goes in the blank?