Korean -거든요: Giving the Reason After the Fact

In English you can say "I can't come. I have work." and let the listener connect the dots. Korean has an ending built for exactly that move: you state the main point first, then attach the reason or background with -거든요, as if adding "...because, you see, I have work." It's one of the most common endings in spoken Korean, and it's easy to misplace because it works backwards from the -아/어서 pattern most learners meet first.

How to form it

-거든요 attaches directly to the stem. There's no 으 to worry about and no stem change, because 거 starts with a consonant.

Stem	+ -거든요	Example
바쁘다 (busy)	바쁘거든요	요즘 많이 바쁘거든요. — I've been really busy lately.
춥다 (cold)	춥거든요	저는 추위를 많이 타요. 겨울에는 방이 춥거든요. — I feel the cold a lot. My room is cold in winter, you see.
이다 (to be)	-이거든요	저는 아직 학생이거든요. — I'm still a student, you see.
Past tense	-았/었거든요	어제 잘 못 잤거든요. — I didn't sleep well yesterday.

For something that already happened, put the past marker before 거든요: 갔거든요, 바빴거든요, 못 잤거든요.

The main job: reason after the result

The pattern is two sentences. First the thing you want to say, then -거든요 for the explanation behind it.

• 오늘은 일찍 잘 거예요. 내일 아침 6시에 일어나야 하거든요. — I'm going to bed early today. I have to get up at 6 tomorrow, you see.
• 오늘 너무 피곤했어요. 어젯밤에 두 시간밖에 못 잤거든요. — I was so tired today. I only slept two hours last night.
• 그 카페에 자주 가요. 거기 커피가 정말 맛있거든요. — I go to that café often. The coffee there is really good.

It also works as a direct answer to a "why?":

왜 안 먹어요? — Why aren't you eating? 저는 매운 음식을 못 먹거든요. — I can't eat spicy food, you see.

The second job: setting the scene

-거든요 can also introduce background information that the next sentence builds on. Here the "reason" isn't explaining a result. It's laying down context the listener needs before the story starts:

• 어제 지하철에서 좀 이상한 일이 있었거든요. 옆에 앉은 아저씨가 갑자기 노래를 시작했어요. — Something odd happened on the subway yesterday. The man sitting next to me suddenly started singing.

This is handy for diary entries that tell a small story, but it's still spoken-sounding. In a diary written in plain style (-았다, -이다), -거든요 adds a chatty tone, like you're talking to the page.

-거든요 vs -아/어서 vs -잖아요

All three can sit near a reason, but they point in different directions.

	Where the reason goes	What it assumes about the listener
-아/어서	Before the result, in one sentence	Nothing special
-거든요	After the result, as its own sentence	The listener doesn't know this yet
-잖아요	Anywhere it fits as a reminder	The listener already knows this

The same fact in the three patterns:

• 일이 많아서 못 가요. — I can't go because I have a lot of work.
• 못 가요. 일이 많거든요. — I can't go. I have a lot of work, you see.
• 못 가요. 일이 많잖아요. — I can't go. I have a lot of work, remember?

The trap: putting the reason first

Because -아/어서 puts the reason before the result, it's tempting to do the same with -거든요:

일이 많거든요 못 가요. ✗ 일이 많아서 못 가요. ✓ 못 가요. 일이 많거든요. ✓

-거든요 closes a sentence. The main point has to come before it, in the sentence you've already said, and the reason follows. If you want the reason first, switch to -아/어서.

The trap: forgetting the past marker

When the reason happened earlier, -거든요 needs the past ending, like any other sentence ending:

오늘 늦었어요. 어젯밤에 잘 못 자거든요. ✗ 오늘 늦었어요. 어젯밤에 잘 못 잤거든요. ✓ — I was late today. I didn't sleep well last night.

The trap: using it for something the listener already knows

-거든요 delivers information as news. If both of you already know the fact, it can sound odd, as if you're explaining something obvious. Reach for -잖아요 instead:

우리 내일 쉬거든요. △ (sounds like breaking news when you both know tomorrow is a day off) 우리 내일 쉬잖아요. ✓ — We're off tomorrow, remember?

Tone matters here too. Depending on the intonation, a string of -거든요 sentences can come across as making excuses, so use it where "here's why" is what you actually mean.

Try it in tonight's entry

Write one sentence about what you did or felt today, then add the reason with -거든요:

• 오늘은 집에서 쉬었어요. 어제 너무 많이 걸었거든요.
• 요즘 일기를 써요. 한국어 실력을 늘리고 싶거든요.

State the point first, add the reason second, and keep the past marker if the reason is already over.