Indicating a Reason with '서'

01

Conjugation Rules

• If the last vowel of the stem is ㅏ (a) or ㅗ (o), add 아서 (a·sŏa·seoa·sŏa·se).
• If the last vowel is anything else, add 어서 (ŏ·sŏeo·seoŏ·sŏe·se).
• If the verb ends in 하다 (ha·daha·daha·daha·ta), it becomes 해서 (hæ·sŏhae·seohae·sŏhay·se).

• 배가 고파서 밥을 먹어요.

  bæ·ga go·pʰa·sŏ ba·bŭl mŏ·gŏ·yo.bae·ga go·pa·seo ba·beul meo·geo·yo.bae·ga go·p'a·sŏ ba·bŭl mŏ·gŏ·yo.pay·ka ko·pha·se pa·pul me·ke·yo.

  I am hungry, so I am eating rice.

• 비가 와서 집에 있어요.

  bi·ga wa·sŏ ji·be i·ssŏ·yo.bi·ga wa·seo ji·be i·sseo·yo.bi·ga wa·sŏ ji·be i·ssŏ·yo.pi·ka wa·se ci·pey i·sse·yo.

  It is raining, so I am at home.

• 피곤해서 자고 싶어요.

  pʰi·gon·hæ·sŏ ja·go si·pʰŏ·yo.pi·gon·hae·seo ja·go si·peo·yo.p'i·gon·hae·sŏ ja·go si·p'ŏ·yo.phi·kon·hay·se ca·ko si·phe·yo.

  I am tired, so I want to sleep.

02

Tense Restrictions

A crucial rule for 서 (sŏseosŏse) is that you cannot attach past tense markers (like 았 (at) or 었 (ŏteotŏtet)) directly before it. The tense of the entire sentence is determined solely by the final verb at the end of the sentence. Even if the reason happened in the past, the verb with 서 (sŏseosŏse) remains in its base conjugated form.

• 어제 아파서 병원에 갔어요.

  ŏ·je a·pʰa·sŏ byŏng·wŏ·ne ga·ssŏ·yo.eo·je a·pa·seo byeong·wŏ·ne ga·sseo·yo.ŏ·je a·p'a·sŏ byŏng·wŏ·ne ga·ssŏ·yo.e·cey a·pha·se pyeng·wŏ·ney ka·sse·yo.

  I was sick yesterday, so I went to the hospital.

• 돈이 없어서 못 샀어요.

  do·ni ŏp·sŏ·sŏ mot sa·ssŏ·yo.do·ni eop·seo·seo mot sa·sseo·yo.do·ni ŏp·sŏ·sŏ mot sa·ssŏ·yo.to·ni ep·se·se mot sa·sse·yo.

  I didn't have money, so I couldn't buy it.

03

Social Expressions: Thanks and Apologies

This grammar point is the standard way to give a reason for emotions, specifically when greeting, thanking, or apologizing. In these fixed expressions, you cannot use other causal endings like 니까 (ni·ggani·ggani·kkani·kka).

• 만나서 반가워요.

  man·na·sŏ ban·ga·wŏ·yo.man·na·seo ban·ga·wŏ·yo.man·na·sŏ ban·ga·wŏ·yo.man·na·se pan·ka·wŏ·yo.

  Nice to meet you. (Lit: Because we met, I am glad.)

• 늦어서 죄송합니다.

  nŭ·jŏ·sŏ jœ·song·ham·ni·da.neu·jeo·seo joe·song·ham·ni·da.nŭ·jŏ·sŏ joe·song·ham·ni·da.nu·ce·se cway·song·ham·ni·ta.

  I am sorry for being late. (Lit: Because I am late, I am sorry.)

• 도와줘서 고마워요.

  do·wa·jwŏ·sŏ go·ma·wŏ·yo.do·wa·jwŏ·seo go·ma·wŏ·yo.do·wa·jwŏ·sŏ go·ma·wŏ·yo.to·wa·jwŏ·se ko·ma·wŏ·yo.

  Thank you for helping.

04

Restrictions on Commands and Suggestions

You cannot use 서 (sŏseosŏse) when the second clause is a command ("Do this"), a suggestion ("Let's do this"), or a proposal. If you want to give a reason for a command or suggestion, you must use the ending (으)니까 ((ŭ)·ni·gga(ŭ)·ni·gga(ŭ)·ni·kka(ŭ)·ni·kka) instead.

Incorrect: 추워서 코트를 입으세요. (chʰu·wŏ·sŏ ko·tʰŭ·rŭl i·bŭ·se·yo.chu·wŏ·seo go·teu·reul i·beu·se·yo.ch'u·wŏ·sŏ ko·t'ŭ·rŭl i·bŭ·se·yo.chu·wŏ·se ko·thu·lul i·pu·sey·yo.) (It's cold, so please wear a coat.)

Correct: Use (으)니까 ((ŭ)·ni·gga(ŭ)·ni·gga(ŭ)·ni·kka(ŭ)·ni·kka) for this situation.

• 추우니까 코트를 입으세요.

  chʰu·u·ni·gga ko·tʰŭ·rŭl i·bŭ·se·yo.chu·u·ni·gga go·teu·reul i·beu·se·yo.ch'u·u·ni·kka ko·t'ŭ·rŭl i·bŭ·se·yo.chu·u·ni·kka ko·thu·lul i·pu·sey·yo.

  It is cold, so please wear a coat.

• 시간이 없으니까 빨리 가요.

  si·ga·ni ŏp·sŭ·ni·gga bbal·li ga·yo.si·ga·ni eop·seu·ni·gga bbal·li ga·yo.si·ga·ni ŏp·sŭ·ni·kka ppal·li ga·yo.si·ka·ni ep·su·ni·kka ppal·li ka·yo.

  We don't have time, so let's go quickly.

05

Summary of Differences

While both 서 (sŏseosŏse) and (으)니까 ((ŭ)·ni·gga(ŭ)·ni·gga(ŭ)·ni·kka(ŭ)·ni·kka) translate to "because/so", remember these distinctions:

• Focus: 서 (sŏseosŏse) focuses on the result (what happened). (으)니까 ((ŭ)·ni·gga(ŭ)·ni·gga(ŭ)·ni·kka(ŭ)·ni·kka) focuses on the reason (why it happened).
• Usage: Use 서 (sŏseosŏse) for general cause-and-effect and apologies. Use (으)니까 ((ŭ)·ni·gga(ŭ)·ni·gga(ŭ)·ni·kka(ŭ)·ni·kka) for commands, suggestions, and personal justifications.