善悪の区別がつく

know right from wrong

→ 善悪
phrase Rare #45,728
know right from wrong Literally, “the distinction between good and evil is clear.” Often used to describe whether someone can tell right from wrong.
JA: 子供でも善悪の区別がつく。
EN: Even a child can tell right from wrong.

もし彼らが善悪の区別がつくのなら、なぜ君にできないんだろう?

If they can tell right from wrong, why can't you?

— バジュランギおじさんと、小さな迷子 (2015)

その子は善悪の区別がつくようになった。

That child has learned to distinguish right from wrong.