Korean: Giving Reasons with 왜냐하면 and -아서/-어서
Learn to explain why you think something in Korean using 왜냐하면 ... 때문이다 and the -아서/-어서 ending, so you can support simple opinions politely.
By LiamCulture & nuance · Yapr Learn
When you give an opinion in Korean, people often expect a reason. The most useful tools are the adverb 왜냐하면 (because) and the verb ending -아서/-어서 (because/since). 왜냐하면 usually introduces a full sentence that ends with 때문이다 (it is because), while -아서/-어서 attaches directly to a verb or adjective stem. This lesson teaches both patterns at elementary level, with polite -요 style. You will practice linking a short opinion to a clear reason, which is the core of basic argumentation in Korean.
By the end, you can…
- give a simple reason for my opinion using 왜냐하면 ... 때문이다.
- link two clauses with -아서/-어서 to say 'because' or 'since'.
Listen once. Try it slowly. Then say it without looking.
Checking available voices…
비가 와서요.
Because it is raining.
wae-nya-ha-myeon bi-ga wa-seo-yo
Polite spoken reason; -아서요 softens the ending. 왜냐하면 is not used with -아서/-어서 in the same clause.
시간이 없기 때문이에요.
It is because I do not have time.
wae-nya-ha-myeon si-ga-ni eop-ki ttae-mun-i-e-yo
Polite 때문이에요 pattern; useful when explaining a decision. 왜냐하면 can precede it, but it is optional.
저는 집에 가요. 피곤해서요.
I am going home. Because I am tired.
jeo-neun ji-be ga-yo. pi-gon-hae-seo-yo
-해서 is the common 'because' ending for 하다 verbs and adjectives like 피곤하다.
이 옷이 좋아요. 싸서요.
I like these clothes. Because they are cheap.
i o-si jo-a-yo. ssa-seo-yo
싸다 becomes 싸서요; the reason follows the opinion in a separate short sentence.
오늘은 못 가요. 일이 있어서요.
I cannot go today. Because I have work.
o-neu-reun mot ga-yo. i-ri i-sseo-seo-yo
있어서요 comes from 있다 + -어서요; a very common polite excuse.
Pronunciation guides are approximate. Slow playback keeps the original pitch.
Make it make sense
Useful pattern
The pattern 왜냐하면 + reason + 때문이다 lets you state a reason as a complete sentence. In polite speech, use 때문이에요: 왜냐하면 오늘 바빠요. 그래서 못 가요. (Because I am busy today, I cannot go.) A tighter pattern is verb/adjective stem + -아서/-어서: 바빠서 못 가요 (I cannot go because I am busy). Use -아서 after stems with ㅏ or ㅗ, and -어서 after most other vowels: 좋아서 (because it is good), 피곤해서 (because I am tired).
When to use it
Use 왜냐하면 ... 때문이에요 when you want to sound explicit and a little formal, for example when explaining a plan to a teacher or colleague: 왜냐하면 내일 시험이 있기 때문이에요 (Because I have an exam tomorrow). Use -아서/-어서 in everyday conversation because it is shorter and natural: 시간이 없어서 안 갔어요 (I did not go because I had no time). Do not use -아서/-어서 before a command or suggestion; for 'because' with those, Korean often uses -니까, which is beyond this lesson.
Listen to each line, then take one part and reply out loud.
주말에 영화 볼래요?
Do you want to see a movie this weekend?ju-ma-re yeong-hwa bol-lae-yo미안해요, 못 가요. 숙제가 많아서요.
Sorry, I cannot go. Because I have a lot of homework.mi-an-hae-yo, mot ga-yo. suk-je-ga ma-na-seo-yo아, 그래요? 그럼 다음 주는 어때요?
Oh, really? Then how about next week?a, geu-rae-yo? geu-reom da-eum ju-neun eo-ttae-yo좋아요. 다음 주에는 시간이 있어서 갈 수 있어요.
Good. Next week I have time, so I can go.jo-a-yo. da-eum ju-e-neun si-ga-ni i-sseo-seo gal su i-sseo-yoA little context goes a long way
Korean often places the reason after the opinion, as in 못 가요. 바빠서요. This sounds softer and less confrontational than leading with a long excuse. With strangers or in workplace settings, 왜냐하면 ... 때문이에요 can sound more formal and complete; with friends, -아서/-어서 alone is usually enough.
One thing to watch for
Using 왜냐하면 with -아서/-어서 in the same clause, as in 왜냐하면 바빠서요.
Try this instead: Choose one pattern. Say 왜냐하면 바빠요 or 바빠서요. If you want the full 'because' sentence, use 왜냐하면 바쁘기 때문이에요 (Because I am busy).
Your turn
Try answering out loud before checking a possible answer.
1Turn 'I am tired' into a polite reason with -아서/-어서: 피곤하다 → ?
Show a sample answer
피곤해서요.
피곤하다 is a 하다 adjective, so the stem 피곤하- takes -여서, which contracts to 해서: 피곤해서요. 피곤하니까요 is also grammatical but uses a different ending.
2Complete the sentence: 왜냐하면 내일 시험이 ___ .
Show a sample answer
있기 때문이에요.
The pattern 왜냐하면 ... 때문이에요 needs a noun-like form before 때문이에요. 있기 is the nominalized form of 있다. 있어서요 would change the structure and is not used after 왜냐하면 in this pattern.
3You want to say 'I cannot go because I have work.' Which is more natural in casual polite speech?
Show a sample answer
일이 있어서 못 가요.
-어서 links the reason directly to the result, which is common in everyday polite speech. 왜냐하면 일이 있기 때문이에요 is also correct but sounds more formal and explicit.
Give your opinion first, then add the reason with -아서/-어서 for everyday talk or 왜냐하면 ... 때문이에요 when you need a clear, formal explanation.
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