A2
기 전에 and (으)ㄴ 후에 — before and after
How Korean orders events with 기 전에 and 은 후에, and the 고 나서 form used for a close sequence.
Both turn a clause into something a time word can attach to, and each demands a particular ending regardless of when the event happened.
기 전에 — before
기 makes the verb into a noun; 전 is before.
자기 전에 이를 닦아요.
Jagi jeone ireul dakkayo.
I brush my teeth before bed.
한국에 오기 전에 한국어를 배웠어요.
Hanguge ogi jeone hangugeoreul baewosseoyo.
I studied Korean before I came to Korea.
The whole sentence is in the past and 오기 carries no tense at all. The final verb holds it.
한국에 왔기 전에…
한국에 오기 전에…
기 전에 never takes a tense. The ending is fixed and the sentence’s tense lives in its last verb.
(으)ㄴ 후에 — after
The past modifier ending plus 후.
밥을 먹은 후에 산책해요.
Babeul meogeun hue sanchaekaeyo.
I go for a walk after eating.
Again the sentence is about a routine and the modifier is past, for the mirror reason: within the clause, the eating is done. 다음에 and 뒤에 work identically.
With nouns
Both take 의, which as usual is dropped: 식사 전에, 수업 후에.
수업 후에 커피 마실까요?
Sueop hue keopi masilkkayo?
Shall we get coffee after class?
고 나서
Also after, and it insists the first action is finished before the second starts — a tight sequence rather than a loose afterwards.
숙제를 하고 나서 놀아요.
Sukjereul hago naseo norayo.
I play after I’ve finished my homework.
은 후에 would allow anything in between; 고 나서 does not.