HYEJU LANGUAGE LAB · INTERMEDIATE 51 · LESSON 136
-(으)므로because / since / therefore (formal, written)
-(으)므로 gives a reason in a formal, written style: 바닥이 미끄러우므로 조심하십시오 (The floor is slippery, so please be careful). You’ll see it on public notices, in reports, essays and announcements, but rarely hear it in casual talk.
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A situation you already know
You see a sign at a construction site in Seoul.
Construction in progress. No entry.
Official signs love -(으)므로: short, formal and clear. In speech you’d say 공사 중이라서 들어가면 안 돼요.
Build the form
- 미끄럽다 → 미끄러우 + 므로 → 미끄러우므로Complete expression
- 있다 → 있 + 으므로 → 있으므로Complete expression
- 하다 → 하 + 므로 → 하므로Complete expression
- 중 → 공사 중 + 이므로 → 공사 중이므로Complete expression
- 끝나다 (과거) → 끝났 + 으므로 → 끝났으므로Complete expression
- Vowel stem + -므로, consonant stem + -으므로: 하므로, 있으므로.
- ㄹ stems: 알다 → 알므로; ㅂ irregular: 어렵다 → 어려우므로.
- Nouns: N이므로 (이 often kept, even after a vowel in writing: 학생이므로, 무료이므로).
- Past: -았/었으므로 → 끝났으므로, 했으므로.
- Formal notices can end with requests: 위험하므로 들어가지 마십시오.
- Don’t confuse it with -(으)ㅁ으로(써) (“by means of doing”).
Think in Korean · an English-speaker’s guide
- English “as”, “since” or “therefore” in formal writing feel similar.
- Recognize it first: signs, official emails, essays, TOPIK reading. Then use it in your own formal writing.
- In conversation it sounds stiff, like reading a document aloud. Use -아/어서 or -(으)니까 instead.
Six examples in context
The floor is slippery, so please be careful.
This product is sensitive to heat, so keep it out of direct sunlight.
Many people are applying, so please apply early.
All students have submitted the assignment, so we’ll end class today.
Admission is free, so anyone can come in.
Environmental problems are everyone’s problem, so we must solve them together.
Compare with related patterns
-기 때문에
비가 오기 때문에 행사가 취소되었습니다.“Because it’s raining, the event was canceled.” Clear reason, both written and spoken (Lesson 61).
-(으)니까
비가 오니까 우산 가져가세요.“It’s raining, so take an umbrella.” Spoken, often with advice or commands (Lesson 59).
-아/어서
비가 와서 못 갔어요.“I couldn’t go because it rained.” Everyday cause and result (Lesson 58).
| Pattern | Choose it when… |
|---|---|
| -(으)므로 | Formal writing, notices, reports |
| -기 때문에 | Clear reason, written or spoken |
| -(으)니까 | Spoken; fine with commands |
| -아/어서 | Everyday cause → result |
Common mistakes
Too formal for chatting with friends.
ㅂ irregular: 어렵다 → 어려우므로.
ㄹ stems: no 으.
Nouns need 이므로.
Mini practice · six questions
Try each one before opening the answer. Translation answers are models; other natural wording is possible.
- Fill in the blank이곳은 ______ 조용히 해 주십시오. (도서관)
Check answer
이곳은 도서관이므로 조용히 해 주십시오.
Noun → 이므로.
- Fill in the blank오늘은 날씨가 ______ 외출을 자제하시기 바랍니다. (덥다)
Check answer
오늘은 날씨가 더우므로 외출을 자제하시기 바랍니다.
ㅂ irregular → 더우므로.
- Choose the natural form(친구와 대화) 오늘 (바쁘니까 / 바쁘므로) 내일 만나자.
Check answer
바쁘니까
Casual talk → -(으)니까.
- Choose the natural form(안내문) 엘리베이터 점검 중(이므로 / 이니까) 계단을 이용해 주십시오.
Check answer
이므로
Official notice → -(으)므로.
- Fix the mistake이 문제는 쉽으므로 누구나 풀 수 있다.
Check answer
이 문제는 쉬우므로 누구나 풀 수 있다.
쉽다 → 쉬우므로.
- Say it in Korean (formal notice)The road is under repair, so please take a detour.
Check answer
도로 공사 중이므로 다른 길로 돌아가 주십시오.
Notice style → N이므로 + -아/어 주십시오.
Today’s key point
-(으)므로 = because/since in formal writing (signs, reports, essays). Vowel -므로, consonant -으므로, nouns 이므로, past -았/었으므로. In speech, use -아/어서 or -(으)니까.
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