주어 (ju-eo, jueo) · 목적어 (mok-jeok-eo, mokjeokeo) · 보어 (bo-eo, boeo)
Subject, object, and complement each play distinct roles in a sentence as doer, receiver, and descriptor, with clear differences in position and function.
One lane per word — no nested boxes, just the gist.
The word that acts as the doer or the subject of the action or state in a sentence
When to use
agent of action, state subject, sentence initial position
The nuance
The subject usually appears at the beginning of the sentence and acts as the agent of the verb.
The word that is the target or receiver of the action, typically affected by a transitive verb
When to use
target of action, after transitive verb, receiver of action
The nuance
The object follows a transitive verb and clarifies the target of the action.
A word that supplements or describes the state or identity of the subject or object
When to use
supplement state, after subject/object, with predicate
The nuance
The complement appears after the subject or object and is used with predicates like '이다' or '되다' to describe or identify.
철수가 밥을 먹었다.
cheol-su-ga bap-eul meok-eoss-da., cheol su ga bap eul meok eoss da.
'철수' is the subject and '밥' is the object correctly used.
밥을 철수가 먹었다.
bap-eul cheol-su-ga meok-eoss-da., bap eul cheol su ga meok eoss da.
Although object '밥' comes first, the sentence is natural with subject '철수' after.
철수가 행복하다.
cheol-su-ga haeng-bok-ha-da., cheol su ga haeng bok ha da.
'행복하다' complements the subject '철수' by describing its state.
철수가 밥이 먹었다.
cheol-su-ga bap-i meok-eoss-da., cheol su ga bap i meok eoss da.
'밥이' is a complement, not an object, so it cannot replace the object position here.
나는 책을 읽는다.
na-neun chaek-eul ik-neun-da., na neun chaek eul ik neun da.
'나는' is subject and '책을' is object correctly used.
책을 나는 읽는다.
chaek-eul na-neun ik-neun-da., chaek eul na neun ik neun da.
Object '책을' can come first, subject '나는' after, still grammatically correct.
그는 선생님이다.
geu-neun seon-saeng-nim-i-da., geu neun seon saeng nim i da.
'선생님이다' acts as a complement describing the subject '그는'.
그는 선생님을이다.
geu-neun seon-saeng-nim-eul-i-da., geu neun seon saeng nim eul i da.
The complement cannot take the object particle '을'.
Which sentence has the correct subject?
Which sentence uses the object incorrectly?
Which sentence contains a complement?
