-거든

-거든 means 'if / when (that happens), then …', and the second clause is usually a request, suggestion or intention.

조건·가정Conditions & what-ifs

Han: A general fact in the second clause needs -(으)면, not -거든.

Examples

집에 도착하거든 전화하세요.Call me when you get home.

모르는 게 있거든 언제든지 물어보세요.If there's anything you don't know, ask any time.

시간이 있거든 같이 저녁 먹읍시다.If you have time, let's have dinner together.

V/A+거든

도착하다 → 도착하거든, 시간이 있다 → 시간이 있거든

The second clause should be a command, suggestion or 'I will' — not a plain statement of fact.
Sentence-final -거든요 is different: it gives a reason ('you see, …').

Wrong: ~~봄이 오거든 꽃이 펴요.~~

Right: 봄이 오면 꽃이 펴요.

A general fact in the second clause needs -(으)면, not -거든.

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