biga omyeon jajeongeo daesin jihacheoreul tayo.

If it rains, I take the subway instead of a bicycle.

Breakdown of biga omyeon jajeongeo daesin jihacheoreul tayo.

• ~을: object particle
• ~가: subject particle
• 자전거: bicycle
• 지하철: subway

Questions & Answers about biga omyeon jajeongeo daesin jihacheoreul tayo.

What does -면 mean here, and is it if or when?

-면 is a conditional ending meaning if or when, depending on context. In this sentence it’s often understood as a habitual when/if it rains, I take the subway instead of a bike.

• 비가 오면 … = If/When it rains, …
  If you want to emphasize a one-time future possibility, if fits well; for a routine, when often sounds more natural in English.

Why is it 비가 and not 비는 or 비를?

비가 오다 literally means rain comes/falls, so 비 is the subject of 오다, and the subject particle -가 is natural.

• 비가 와요 = It rains
  비는 could be used for contrast or topic-setting (e.g., As for rain, it’s coming…), but the neutral default is 비가.
  비를 is generally not used because 비 isn’t the object of 오다.

Is 비가 오면 the same as 비가 올 때?

They overlap but aren’t identical.

• 비가 오면 focuses on the condition: if/when it rains, then… (cause/condition → result).
• 비가 올 때 means when it rains / at the time it rains and is more purely time-based.
  For routines, both can work, but -면 often feels more like condition → choice/action.