それならin that case; then
You take what you have just learned as given and say what you will do or suggest: "in that case", "then". Mostly it answers something the other person said.
You can't make it today? Then let's make it tomorrow.
How to form it
What you have just learned。 それなら、+ what you will do or suggest
Friends often say だったら. Staff speaking to a customer say それでしたら or でしたら.
- After it
- A suggestion, a decision, an offer or advice. Now and then, what the news lets you conclude: それなら、大丈夫ですね.
- Where you'll meet it
- Conversation, polite or casual. In writing, mostly dialogue.
In use
Tomorrow's meeting has been moved online.
In that case, I'll join from home.
I heard the place by the station is closed today.
Then let's look for somewhere else.
だったら, それでしたら
I'm a bit nervous about going on my own.
Then shall I come with you?
Do you have a slightly smaller one?
In that case, how about this one?
A customer and a salesclerk.
それならよかった
Once a worry is cleared up, people say それならよかった: "oh, good".
Sorry I'm late. Have you been waiting long?
No, I just got here.
Close neighbours
じゃあ・ではN5
Lighter, and it does more: it also starts things off and opens a goodbye. それなら needs news to answer.
It's raining. Then let's go by bus.
ならN4
The same word on the end of a noun or a clause: you say again the part you are answering. それ stands for all of it.
If you are going by car, you should reserve parking early.
そしたらN3
Casual. In a reply it is a light "then". Telling a story it is "and then", which それなら never is.
You're busy this week? Then shall we make it next week?
それなのにN2
"And yet": what happened clashes with what should have followed, and you say it as a complaint or in disbelief.
I sent two confirmation emails. And yet, the reservation had not been recorded.
それにしてもN2
"Even so", "still": you grant what was just said, and this is still more than you expected.
Of course it's hot: it's August. Still, today's heat is awful.
Check yourself
1Which one fits B's reply?
A
Choose an answer to see why.
2Nobody has said anything yet. The teacher walks in and begins the class. Which one fits?
（ ）、
Choose an answer to see why.
More detail
それならそうと
それならそうと言ってよ is "you should have said so".
You can't come? Then you should have told me sooner.
それなら見たよ
When それ is a thing just named, なら takes it up: "that one".
That movie? I saw that one last week.