biga omyeon jajeongeoreul taji malgo jihacheoreul tayo.

If it rains, don’t ride a bicycle; take the subway instead.

Breakdown of biga omyeon jajeongeoreul taji malgo jihacheoreul tayo.

• ~을: object particle
• ~를: object particle
• ~가: subject particle
• 타다: to ride

Questions & Answers about biga omyeon jajeongeoreul taji malgo jihacheoreul tayo.

What does -면 in 오면 mean?

-면 means if or when.

So:

• 비가 오다 = to rain
• 비가 오면 = if it rains / when it rains

In Korean, -면 attaches to a verb stem to make a condition:

• 가다 → 가면 = if/when someone goes
• 먹다 → 먹으면 = if/when someone eats
• 오다 → 오면 = if/when it rains / if/when it comes

In this sentence, 비가 오면 sets the condition for the advice that follows.

Why is it 비가 오면, not 비는 오면?

Because 비가 오다 is the normal way to say it rains.

Here, 비 is the subject of the verb 오다 in the weather expression 비가 오다. That is why 가 is used.

• 비가 와요 = It rains / It’s raining
• 눈이 와요 = It snows / It’s snowing

You can use 비는 in some contexts, but it changes the nuance. 는 would make 비 the topic, often with contrast:

• 비는 오지만... = As for rain, it does fall, but...
• 비는 오면 안 돼요 = Rain, if it comes, is bad / It must not rain

For a plain conditional statement, 비가 오면 is the most natural.