-고 해서: Partly Because — One Reason Among Others

-고 해서 is how Korean often says one reason among others without swearing it was the only cause.

Curriculum gloss: partly because — one reason among several. There is no dedicated 우리말샘 headword for the whole string; it is a taught chunk: connective -고 plus 해서 (하다 + -아서). Teaching grammars read the package as a contributing reason — treat that as classroom Korean, not a separate dictionary sense you must invent.

What it does — soften sole-cause pressure

A bare -아서/어서 can sound like the reason:

어두워서 조명을 바꿨어요.

-고 해서 often feels more like among the factors:

어둡고 해서 조명을 바꿨어요.
좁고 해서 가구를 줄였어요.
비싸고 해서 다른 걸 골랐어요.

Interior talk (Unit 4) lives here: you rarely renovate for one pure scientific cause — you bundle discomforts.

Forms

The -고 attaches to the factor you are naming; 해서 lands the “and so / doing that…” hinge. Do not orphan 해서 onto a stem that never took -고.

Near neighbours

어두워서 바꿨어요.           direct cause
어둡고 추워서 바꿨어요.       two -아서 causes
어둡고 해서 바꿨어요.         factor-in-a-bundle feel

When to use — and when a blunt cause is better

Use -고 해서 when explaining a choice and you do not want to sound as if you ran a single-variable experiment.

Prefer -아서/어서 when the cause is clear and sole (비가 와서 취소).

Prefer -으니까 when the reason is a spoken premise for a suggestion or claim.

Practice rule: if “partly because…” would be honest English, -고 해서 is licensed. If “because — full stop” is honest, use a direct cause ending.