An expression meaning 'Is that so?' used to show realization, surprise, or rhetorical confirmation.
そうか、君があの時の友達だったのか。
Is that so — you were the friend from that time?
そうか…事情はそういうことだったのか。
I see... so that's what the situation was.
そうか、だから来られなかったのかね。
Is that so — that's why they couldn't come, huh?
A casual response meaning 'I see' or 'OK', indicating understanding or acknowledgment.
A: 明日休みになったよ。 B: そうか、じゃあ出かけよう。
A: Tomorrow's a day off. B: I see — then let's go out.
そうか、分かった。仕事を任せてください。
I see, got it. Leave the work to me.
そうか、それは良かったね。
Oh, I see — that's great.