-(으)므로 Grammar in Korean: Meaning and How to Use It

What you'll learn

• Attach -므로 or -으므로 to verb and adjective stems, and (이)므로 to nouns.
• Add 았/었 inside the first clause to show the past.
• Match the pattern with formal endings such as -다, -ㅂ니다 and -십시오.
• Tell -(으)므로 apart from -기 때문에, -(으)니까 and the look-alike -ㅁ으로써.

Prerequisites: the lessons on -기 때문에 and -(으)니까. Time: about 15 minutes.

Key facts

• Form: -므로 after a vowel or ㄹ; -으므로 after a final consonant; nouns take (이)므로.
• The past goes inside the first clause: 왔으므로, 길어졌으므로.
• In everyday talk, use -아/어서 or -(으)니까 instead.
• It sounds the same as the noun form plus 으로 (읽음으로), which means "by doing."

Listen to two model sentences.

The next section defines the pattern.

What Does -(으)므로 Grammar Mean?

-(으)므로 is a connective ending that gives the reason or ground for what follows. Read it as "because," "since" or "therefore." The first clause states a fact, and the second clause draws a conclusion from it.

The ending belongs to formal and written Korean. Signs say 위험하므로 들어가지 마십시오 ("It is dangerous, so do not enter"). Reports say 비가 많이 왔으므로 행사가 취소되었다 ("Because it rained a lot, the event was cancelled"). A friend would say 비가 와서 행사가 취소됐어요 instead.

The first example ends with a formal request, and the second with a plain written statement. Both pair the reason with a formal ending. The next section shows how to form the pattern.

How Do You Form -(으)므로?

Attach the ending to the stem, which is the dictionary form without 다. The stem's last sound picks the shape.

Stems Ending in a Vowel

Add 므로 directly. The same rule covers 하다 verbs and adjectives.

The RR of 부족하므로 is bujokameuro, because RR writes the aspirated [ㅋ] that comes from ㄱ and ㅎ meeting in a predicate. The spoken form is [시가니 부조카므로 발표는 다음 주에 하겓씀니다.].

Stems Ending in a Consonant

Add 으므로. The 으 is the linking vowel that lets the ending follow a final consonant.

Spoken, 많으므로 is [마느므로] and 읽으므로 is [일그므로], because the final sound moves to the next syllable. The sentence 사용자가 많으므로 서버를 늘렸다 means "Because there are many users, we added servers."

Irregular Stems and Nouns

• ㄹ stems keep ㄹ and take -므로, with no 으. 만들다 becomes 만들므로, and 알다 becomes 알므로. This is the same pattern as -(으)면 (만들면). The ㄹ does not drop here, because the ending begins with ㅁ, not ㄴ.
• ㅂ-irregular stems change ㅂ to 우 before 으. 춥다 becomes 추우므로, 어렵다 becomes 어려우므로. The sentence 날씨가 추우므로 따뜻하게 입으시기 바랍니다 means "Because it is cold, please dress warmly."
• Past tense puts 았/었 inside: 왔으므로, 길어졌으므로. The last verb also shows the tense.
• Honorific puts 시 inside: 바쁘시므로. The sentence 선생님께서 바쁘시므로 내일 다시 오십시오 means "The teacher is busy, so please come again tomorrow."
• Nouns take 이다, giving (이)므로. After a consonant it is 이므로: 학생이므로, 문서이므로. After a vowel the full 이므로 is also used in writing: 의사이므로.

The next section builds a full sentence.

Worked Example: Building 이 길은 위험하므로 들어가지 마십시오

Say that a road is dangerous and you want to tell people to stay out. Follow five steps.

1. Write the reason. "This road is dangerous" is 이 길은 위험하다. The stem is 위험하.
2. Check the last sound. 하 ends in a vowel, so the ending is 므로.
3. Add 므로. 위험하 + 므로 = 위험하므로.
4. Write the result. "Do not enter" is 들어가지 마십시오. The ending -(으)십시오 is the formal polite request, and 마십시오 is its negative.
5. Join the parts. 이 길은 위험하므로 들어가지 마십시오.

You'll know it worked when the first clause ends in -므로 with no 요, a formal ending closes the sentence, and the result is a conclusion drawn from the reason. If you wanted to explain the same thing to a friend, you would say 이 길은 위험하니까 들어가지 마세요.

The next section covers tense and sentence types.

Which Tenses and Sentence Types Work with -(으)므로?

The first clause can show past tense, and the last verb carries the sentence's style.

In plain writing, the main clause ends in -다: 사용자가 많으므로 서버를 늘렸다. In formal speech it ends in -ㅂ니다: 저는 학생이므로 할인을 받을 수 있습니다 ("Because I am a student, I can get a discount"). In notices, a formal request or command closes the sentence: 위험하므로 들어가지 마십시오.

Casual commands are different. In everyday talk, a command after a reason uses -(으)니까 (비가 오니까 우산을 가져가세요). Do not use -(으)므로 for that. The pattern is for writing and formal contexts, where a request ends in -십시오 or -기 바랍니다.

The next section compares -(으)므로 with -기 때문에 and -(으)니까.

How Is -(으)므로 Different from -기 때문에?

All three give a reason. The differences are register, feeling and what can follow.

Compare these three sentences about the same rain.

• 비가 많이 왔으므로 행사가 취소되었다. A formal report.
• 비가 오기 때문에 행사가 취소되었다. Also written, with the reason stated firmly. The ending -기 때문에 can also close a sentence: 비가 왔기 때문이다.
• 비가 오니까 우산을 가져가세요. A reason that leads to a command in everyday talk.

-기 때문에 is the broader choice. It works in speech and writing, and you can end a sentence with -기 때문이다. -(으)므로 is narrower: it lives in notices, rules, contracts and academic prose. If you are unsure which to use, -기 때문에 is the safer one.

The next section covers look-alikes and edge cases.

Variations and Edge Cases of -(으)므로

The Sound-Alike -ㅁ으로(써)

The noun form of a verb adds ㅁ to the stem: 읽다 becomes 읽음. Add 으로써 and you get "by doing": 책을 많이 읽음으로써 어휘가 늘었다 ("By reading a lot, my vocabulary grew"). That sounds exactly like -(으)므로, which would be 읽으므로. Both are said [일그므로].

The meanings differ. 읽으므로 gives a reason ("since he reads"), and 읽음으로써 gives a means ("by reading"). Spelling and context tell them apart. Look at the second clause: if it names a result of an action (어휘가 늘었다), you probably have "by doing."

Notice Language

Signs and rules use -(으)므로 with set requests: 잠겨 있으므로 사용할 수 없습니다 ("It is locked, so it cannot be used"). The phrase -ㄹ 수 없습니다 ("cannot") is typical here.

Stopping before the Result

You do not end a sentence with -(으)므로. It is always followed by a result clause. In spoken Korean, people do end sentences with -(으)니까 or -거든요, but not with -(으)므로.

The next section lists the mistakes that appear most often.

What Mistakes Do Learners Make with -(으)므로?

Learners make six predictable mistakes. Each has a reason and a fix.

Learners often use it in casual speech. Actually -(으)므로 sounds formal and a little stiff. Casual example: 비가 오므로 집에 있어요 sounds like a notice. Fix: say 비가 와서 집에 있어요 or 비가 오니까 집에 있어요.

Learners often put a casual command after it. In everyday talk, 비가 오므로 우산을 가져가세요 sounds out of place. Fix: use -(으)니까 for a casual command, or a formal ending such as -십시오 or -기 바랍니다 in a notice.

Learners often drop ㄹ from ㄹ stems. Wrong: 만드므로. Right: 만들므로. Fix: ㄹ stays before -므로, as in 만들면.

Learners often use 으므로 after a vowel. Wrong: 위험하으므로. Right: 위험하므로. Fix: use 므로 after a vowel.

Learners often leave out 이 after a noun. Wrong: 학생므로. Right: 학생이므로. Fix: a noun needs 이다 first.

Learners often mix it up with -ㅁ으로써. Actually 읽으므로 and 읽음으로써 sound the same, but one is a reason and the other is a means. Fix: check whether the sentence means "since" or "by doing."

The next section gives you practice.

Practice and Answers

Do the four tasks, then compare with the key.

Task 1: add the ending. Write the form with -(으)므로.

1. 위험하다
2. 많다
3. 춥다
4. 만들다
5. 학생 (noun)

Task 2: fix the error. Each sentence has one mistake. Rewrite it correctly.

1. 학생므로 할인을 받을 수 있습니다.
2. 위험하으므로 들어가지 마십시오.
3. 이 제품을 만드므로 가격이 올랐다.

Task 3: translate. Write in Korean: "The time is short, so I will give the presentation next week." and "This document is official, so please keep it."

Task 4: write your own. Write one notice-style sentence with a reason and a formal request, and rewrite it as an everyday sentence with -(으)니까.

Answer key

1. (1) 위험하므로 (2) 많으므로 (3) 추우므로 (4) 만들므로 (5) 학생이므로
2. (1) 학생이므로 할인을 받을 수 있습니다. (2) 위험하므로 들어가지 마십시오. (3) 이 제품을 만들므로 가격이 올랐다.
3. 시간이 부족하므로 발표는 다음 주에 하겠습니다. 이 서류는 공식 문서이므로 보관해 주십시오. Other correct versions exist, for example 보관하시기 바랍니다.
4. Sample answers: 바닥이 미끄러우므로 조심하시기 바랍니다. → 바닥이 미끄러우니까 조심하세요. Any pair is correct if the notice uses -(으)므로 with a formal ending and the everyday one uses -(으)니까.

If task 1 was correct, you have the form rule. If task 2 was hard, review the vowel and consonant endings. The next section points you to what comes after this lesson.

What Should You Learn after -(으)므로 Grammar?

After -(으)므로, review -기 때문에, the broader formal reason, and -(으)니까, the everyday reason that can lead to commands.

For a wider view, the parent page Cause and Reason lists every pattern in this group. -(으)므로 sits at level B2 on the Advanced Grammar list, which is an editorial estimate. For the tense that goes inside the first clause, see past tense -았/었-. TOPIK is run by the National Institute for International Education (NIIED); check topik.go.kr for what the exam covers.

This lesson covers -(으)므로 in written and formal Korean. It does not cover every literary variation. About this page. Last updated 2026-10-09. Revised Romanization follows the national rules and is shown only as a learning aid.

Frequently Asked Questions

What Does -(으)므로 Mean?

-(으)므로 means "therefore", "since" or "because". It gives the reason for the result in the second clause. 이 길은 위험하므로 들어가지 마십시오 means "This road is dangerous, so do not enter." It is a formal, written ending found on signs, in notices, in rules and in reports, rather than in everyday conversation.

How Do I Attach -(으)므로 to a Verb or Adjective?

Remove 다 from the dictionary form. After a vowel add -므로 (위험하므로). After a final consonant add -으므로 (많으므로). ㄹ stems keep ㄹ and take -므로 (만들므로). ㅂ-irregular stems become 우 before 으므로 (추우므로). After a noun use (이)므로, as in 학생이므로.

Can -(으)므로 Be Used in the past Tense?

Yes. Put 았/었 inside the first clause: 비가 많이 왔으므로 행사가 취소되었다. The same 았/었 appears with 하다 verbs (부족했으므로) and with 이다 (학생이었으므로). The last verb also carries the tense. For future meaning, use 겠 or -(으)ㄹ 것이다 in the result clause.

Is -(으)므로 Used in Speech or Only in Writing?

It is mainly written and formal. You will see it in official notices, rules, contracts, academic writing and prepared speeches, with endings such as -다, -ㅂ니다 and -십시오. In everyday talk people use -아/어서 or -(으)니까. Using -(으)므로 with a friend sounds stiff, like reading a sign aloud.

What Is the Most Common Mistake with -(으)므로?

The most common mistake is using it in casual speech or with a casual command, where -(으)니까 fits better. Another is dropping ㄹ from ㄹ stems: write 만들므로, not 만드므로. A third is mixing it up with -ㅁ으로써 ("by doing"), which sounds identical but gives a means, not a reason.

What Is the Difference between -(으)므로 and -기 때문에?

Both give a reason. -(으)므로 is formal and written, and it draws a conclusion from a fact, often in notices and rules. -기 때문에 works in speech and writing, states the reason firmly, and can close a sentence with -기 때문이다. Neither is followed by a casual command; for that use -(으)니까.

Save This to Pinterest