Learn Hardcore Korean: nalssiga joheumyeon bakkeseo norayo. - If the weather is nice, I play outside.

좋으면 is the combination of 좋다 (to be good) and the conditional connector -면, so it means “if/when it’s good.” Attaching -면 to a verb or adjective root expresses a condition or “whenever” something happens.

Why is 가 used after 날씨 instead of 는?

가 is the subject marker, showing that 날씨 is the grammatical subject of 좋으면. Using 는 would make 날씨 the topic, which shifts the nuance to “as for the weather, if it is good…,” placing more emphasis on “weather” itself rather than just stating the condition.

What does 밖에서 mean, and why do we use -에서 here?

밖 means “outside,” and -에서 marks the location where an action takes place. So 밖에서 means “outside (at that place).” Without -에서, 밖 is just the noun “outside,” and 밖에 would mean “only outside” or serve as a limiter in negative sentences.

What tense and politeness level is indicated by 놀아요?

놀아요 is the polite present tense. Koreans use it in everyday polite speech to describe habitual or general actions—here, “(we) play” or “(people) play.”

How would you say the same sentence more casually or more formally?

Casual (to close friends):
날씨가 좋으면 밖에서 놀아.

Formal (to a stranger or in writing):
날씨가 좋으면 밖에서 놉니다.

You keep the structure but change the verb ending to match the politeness level.

Why is the verb 놀다 conjugated as 놀아요 and not 논다?

To form the polite present tense from 놀다, you drop -다 and add -아요 (because the verb stem ends in the vowel ㅗ).
논다 is the plain present tense, used in written narratives or very informal speech.

Can 날씨가 좋으면 밖에서 놀아요 also mean “whenever the weather is good” rather than “if”?

Yes. In Korean, -면 can express a general condition or habitual action—“whenever/any time X happens, Y happens”—not just a one-time future “if.”

Can you explicitly add “we” (as the subject) in Korean?

You can, though Koreans often omit pronouns when context is clear. For example:
저희가 날씨가 좋으면 밖에서 놀아요.
or more naturally:
날씨가 좋으면 저희(가) 밖에서 놀아요.

But even without “we,” it’s perfectly clear who’s playing.