expression
by all rights; properly speaking; normally
Used to state what should happen or be the case according to rules, expectations, or common sense. Often followed by a contrastive が or けど to introduce the actual situation.
本来なら今日中に提出しなければならないが、まだ終わっていない。
By all rights I should submit it today, but I haven't finished yet.
本来なら彼が責任を取るべきだ。
Properly speaking, he should take responsibility.