eeokeoneul kyeoseo bangi siwonhaeyo.

I turned on the air conditioner, so the room is cool.

Breakdown of eeokeoneul kyeoseo bangi siwonhaeyo.

• ~이: subject particle
• ~을: object particle
• ~서: so
• 방: room

Questions & Answers about eeokeoneul kyeoseo bangi siwonhaeyo.

What does 켜서 mean here, and how is it formed?

켜서 comes from the verb 켜다, which means to turn on something like a light, TV, or air conditioner.

It is formed like this:

• 켜다 → verb stem 켜-
• -아서/-어서 attached to the stem
• 켜서

In this sentence, -아서/-어서 connects two ideas:

• 에어컨을 켜서 = turning on the air conditioner / because (someone) turned on the air conditioner
• 방이 시원해요 = the room is cool

So 켜서 links the action and the result.

Why is -서 used instead of -고?

-서 often shows a relationship like:

• cause/result
• reason
• or a natural sequence where the first action leads to the second

So in 에어컨을 켜서 방이 시원해요, the idea is:

• The room is cool because the air conditioner is on
• or I turned on the air conditioner, so the room is cool

If you used -고 instead, it would sound more like just listing two facts:

• 에어컨을 켜고 방이 시원해요

That sounds less natural here because the room being cool is a result of turning on the air conditioner. So -서 is the better choice.