What it means:
To many of us English speakers this seems a little ambiguous. Which is it? “If” or “when”?
The answer is: is there really a difference? Look at the examples below. You could change the “if ” to a “when” in all 3 and they’d actually mean the same thing, wouldn’t they? Context will also make it clear.
How to attach it:
When attaching this particle to a verb or adjective that ends in a consonant, use -으면.
이 밤 (Tonight) by Jin
내 눈을 감으면 ~ “When I close my eyes”
Original verb: 감다 – to close (one’s eyes)
When attaching this particle to a verb or adjective that ends in a vowel, use -면.
그 문을 열고 들어가면 이 곳이 기다릴 거야. ~ “If you open that door and go in, this place will be waiting.”
Original verb: 들어가다 – to go into
And finally, when attaching this particle to a noun, we add -이라면 if the noun ends in a consonant, and -라면 it it ends in a vowel.
만약 게임이라면 ~ “If this is a game.”
Original noun: 게임 – game
Tell me 내 목소리가 가짜라면 ~ “Tell me, if my voice is fake”
Original noun: 가짜 – something fake
One more variation:
This one can only mean “if”, and it’s created by converting the word to diary form before adding 면, instead of just adding it to the root. I can’t explain diary form here. That’s a whole other beast. But let’s at least see a couple of sentences.
내 말을 믿는다면 하나 둘 셋. ~ “If you believe my words, 1 2 3.”
Original verb: 믿다 – to believe, to trust