At a glance
それなら means "if that's the case" or "in that case". You use it to reply to something you have just heard or learned, and then give a suggestion, advice or decision based on it.
A。それなら、B。
「明日は雨が降るそうです。」「それなら、傘を持っていったほうがいいですね。」 "It's supposed to rain tomorrow." "In that case, you'd better take an umbrella."
How to form it
それなら is a connector. It comes at the start of the reply sentence, usually followed by 、.
| Form | Position | Register |
|---|---|---|
| それなら | Start of sentence B | Neutral: fine in polite and casual speech |
| そんなら | Start of sentence B | Casual spoken form |
| なら | Start of sentence B | Casual, short spoken form |
| それでは | Start of sentence B | More formal |
それなら is literally それ "that" + なら "if".