Grammar
N 이후
Meaning
BeginnerN ihu
Attaches to a noun to mean 'since N' or 'after N', anchoring a stretch of time to the point it starts from: 2024년 5월 이후 27개월 연속 is twenty-seven straight months counted from May 2024. Because it names a starting point rather than a gap, it is also how Korean reporting bounds a record — 2022년 7월 이후 가장 높았다 says nothing since that July has been higher, which is a narrower claim than 'the highest ever'.
Form
이후 is a noun, so it follows a noun phrase with a space and takes the particles a noun takes: bare 이후 in the compressed style headlines and statistics writing use, 이후에 for a plain 'after', 이후로 when the stress is on the span running on from that point, 이후에는 when that span is made the topic. What comes in front is normally a date, a period or a named event (2020년 이후, 사고 이후, 취임 이후). It can also stand alone at the head of a sentence meaning 'since then', and it modifies a following noun directly, with no 의 (이후 대책).
Examples
2020년 이후 처음으로 열리는 행사입니다.
It is the first event to be held since 2020.
Common mistakes & nuance
이후 and 후 both translate as 'after', but they are not interchangeable. 후 measures a gap forward from a point — 3일 후 is three days later, a single day — while 이후 opens a span that runs on from the point named, so 3일 이후 is day three onward. That is why streaks and records take 이후 and appointments take 후. The other thing to watch while reading is what the reference point does to the claim: a superlative under 이후 is bounded by that date, so 'the highest since July 2022' quietly leaves open that something higher stands before it. 처음 works the same way — 2020년 이후 처음 is the first since 2020, not the first ever, and the sentence is silent about what happened before that year.
Similar grammar
- -(으)ㄴ 후에
The same 후, on the other side of the sentence. -(으)ㄴ 후에 takes a clause, so the verb in front of it carries the -(으)ㄴ modifier ending (회의가 끝난 후에); N 이후 takes a bare noun (회의 이후). The senses differ too — 후에 places one event after another, while 이후 opens the span that follows, which is why record and streak figures reach for 이후.
- -(으)ㄴ 뒤에
A register split on top of the same clause-versus-noun difference. 뒤 is the native Korean word and attaches to a clause with -(으)ㄴ (흔들림이 멈춘 뒤에); 이후 is Sino-Korean (以後), attaches to a noun, and is the one statistics and official notices use. Where 뒤에 simply puts one event after another, 이후 also carries the 'from then onward' reading that record-keeping needs.