께서
RuleHonored subject + kkeseo: when the subject is someone to be respected, kkeseo replaces i/ga (subject honorification).
Curiosity
When the subject is someone you must honor — a teacher, a grandparent — can you still use the ordinary i/ga?
Intuition
Korean begins showing respect right at the subject slot. kkeseo is a marker that puts a "hat of deference" on the subject in advance: "this person ranks high."
Visualization
Step up one level from a plain subject to an honored one: seonsaengnim-i → seonsaengnim-kkeseo. The i/ga turns into kkeseo.
Honorificsubject honorification
선생님이seonsaengnim-iplain subject (i/ga)
Essence
kkeseo is the entry point of subject honorification and usually pairs with -(eu)si- on the verb: seonsaengnim-kkeseo osimnida ("the teacher is coming"). As a topic it becomes kkeseo-neun. It is not used for friends or those younger/lower than you.
Examples
선생님께서 오십니다.
The teacher is coming. (honorific)
할아버지께서 신문을 읽으세요.
Grandfather is reading the newspaper. (honorific)
어머니께서는 집에 계세요.
As for mother, she is at home. (honorific)
Mini-quiz
"seonsaengnim__ osimnida." (The teacher is coming) — which fits an honored subject?