Causatives show that a person is not acting of their own will. They can be understood as ‘make’, ‘let’ or ’cause’. For example:
보다 (to see) > 보이다 (to show)
벗기다 (to undress) > 벗기다 (to make someone undress)
There are no hard rules for which suffix a stem takes, only some very loose (and contradictory!) patterns:
이: after vowels and sometimes ㄱ
비행기에 탑승하기 전에 모든 승객들은 여권을 보여야 돼요.
Before boarding the plane, all passengers must show their passports.
어렸을 때 어머니가 저에게 모든 채소를 먹였어요.
When I was young my mother made me eat all my vegetables.
히: after ㄷ, ㅂ and sometimes ㄱ
수업마다 선생님이 저에게 교재를 읽혀요.
Every lesson my teacher makes me read from the textbook.
교장 선생님이 아이에게 학생복을 입혀요.
The principal makes us wear a school uniform.
기: after ㄴ, ㅁ, and ㅅ
소년이 누나를 웃겼어요.
The boy made his older sister laugh.
저는 제 친구에게 가장 좋아하는 소설 책을 맡겼어요.
I let my friend keep my favourite novel.
리: after ㄹ and sometimesㅂ
지난 밤에 들은 노래가 저를 울렸어요.
The song I listened to last night made me cry.
군중 사이에서 그의 목소리를 똑똑히 들렸어요.
His voice was clearly audible among the crowd.
우: no real pattern
오늘 아침에 저는 남동생을 깨우는 것을 잊어 버렸어요.
I forgot to wake my younger brother this morning.
아기가 아주 일찍 일어나면 저는 오후에 낮잠을 재워요.
If the baby wakes very early, in the afternoon I let him have a nap.
기사님, 다음 신호등에서 세워 주세요.
Driver, please stop at the next traffic light.
추: no real pattern
영국에는 10월말에 시계를 1시간 늦춰요.
In the UK, clocks are delayed (go back) one hour at the end of October.
소리를 좀 낮춰 주세요.
Please turn the volume down.