Grammar
-(으)므로
Meaning
Advanced-(eu)meuro
A formal written connective that gives the reason for what follows. It says the same thing -기 때문에 does, but attaches straight to the stem with no nominalizer, and it belongs to notices, regulations, rulings and academic writing rather than to conversation. Its usual job is to state a ground that the reader is expected to accept, and then draw the consequence from it.
Form
Verb or adjective stem + -으므로 after a consonant (많다 → 많으므로, 좋다 → 좋으므로) and + -므로 after a vowel (크다 → 크므로, 하다 → 하므로). A stem ending in ㄹ keeps the ㄹ: 만들다 → 만들므로. The past is -았/었으므로 (했으므로, 늘었으므로), and a noun takes N(이)므로 (학생이므로, 무료이므로). It only ever links clauses — it cannot end a sentence, and the sentence-final counterpart is -기 때문이다.
Examples
신청자가 많으므로 일찍 오시는 것이 좋습니다.
Since there are many applicants, it is better to come early.
Common mistakes & nuance
The trap here is spelling, and native writers fall into it too: -(으)므로 gives a reason, while -(으)ㅁ으로(써) means 'by ~ing' and names a means (참여함으로써 도움이 됩니다, 'it helps by taking part'). The test is substitution — if 때문에 fits, the form is -(으)므로. One thing -(으)므로 can do that -아서/어서 cannot is stand in front of an instruction: 위험하므로 접근하지 마십시오 is ordinary signage Korean.
Similar grammar
- 때문에
Same reason relation, different build and different register. 때문에 needs a noun in front of it, or a clause turned into one with -기 (비가 왔기 때문에), and it is the form you hear as well as read. -(으)므로 goes straight onto the stem with no -기 and is markedly stiffer — official notices and written rulings rather than speech.
- -아서/어서
-아서/어서 is the everyday reason connective, and it has two limits -(으)므로 does not: no tense marker can go in front of it (아팠어서 is not a form, only 아파서), and it cannot be followed by a command or a proposal. -(으)므로 takes 았/었 freely (늘었으므로) and is at home in front of an instruction.