Why do causal subordinate clauses ending in -から take だ as a means to connect nouns and な adjectives (e.g. 日本人だから), whereas causal subordinate clauses ending in -ので take な (e.g. 日本人なので)?
I read that だ derives from て+ある, whereas な derives from に+ある, but why would one causal conjunction require で, whereas another one requires に?
Just trying to make sense of it all…
Thank you!