What it means
それなら means “if that is the case,” “then,” or “in that situation.” It responds to information just mentioned or understood and introduces a conclusion, decision, offer, or recommendation based on that information. It commonly appears at the beginning of a sentence and has a conversational but standard tone. The expression itself does not change for politeness; the clause that follows it determines the sentence’s register.
Usage note
それなら refers back to an already established situation, so it is not normally used as a simple replacement for なら when directly attaching a condition to a noun or clause. For a direct conditional, use the appropriate なら construction instead.
Example sentences
来週は図書館が休館になるそうです。それなら、必要な本を今日のうちに借りておきましょう。
Apparently, the library will be closed next week. If that’s the case, let’s borrow the books we need today.
明日は午後から大雪になるそうです。それなら、朝のうちに食料を買っておいたほうがよさそうです。
I hear that there will be heavy snow from tomorrow afternoon. If that’s the case, it seems we had better buy food in the morning.
この電車