Counting things: why 하나 becomes 한
Two number systems, and when each one shows up
Korean has native numbers and Sino-Korean numbers.
Native (하나, 둘, 셋…) count objects, people, hours, age. Sino-Korean (일, 이, 삼…) handle minutes, money, dates, phone numbers, floors.
Before a counter, the first four numbers shorten.
하나→한, 둘→두, 셋→세, 넷→네, 스물→스무. So it is 사과 한 개, never 하나 개.
Counters are not optional.
사람 → 명, 물건 → 개, 동물 → 마리, 종이 → 장, 병 → 병, 잔 → 잔. Saying 사과 세 without 개 sounds unfinished.
Time mixes both systems in one breath.
세 시 삼십 분 — 3 (native) o'clock 30 (Sino) minutes. This is not an exception you can avoid; it appears in every appointment you make.