When I read the word 이르러서는, I was reminded of something I learned sometime in the past. There are three 이르다 in my dictionary, and two of them change to 일러 when the polite ending 요 or certain conjuctions are added, but one of them changes to 이르러. The three 이르다 are as follows:
오늘날에 이르러서는 생활이 복잡해지고 人口도 많아져 그에 맞는 여러 종류의 집이 開發되었다.
Today a variety of house styles have been developed to match our more complex lives and larger population.
- 이르다 (이르러) 1) reach; arrive 2) extend to; come to
- 이르다 (일러) 1) say 2) explain; teach 3) tell; report 4) tell on (a person)
- 이르다 (일러) 1) early 2) premature
The first 이르다 is the one that appeared in the story I was reading.