英語の Yes / No は4つあった
Will they not go? — Yes, they will.
Will they not go? — No, they will not.
Will they go? — Yea, they will.
Will they go? — Nay, they will not.
引用元：Yes and no - Wikipedia
本来のニュートラルな肯定語は "Yea" だった
それを強調し、否定疑問文を二重否定して肯定を強調するのが "Yes"
Old English gise, gese "so be it!," probably from gea, ge "so" (see yea) + si "be it!,"
引用元：yes | Etymology of yes by etymonline
No と Nay の使い分けの由来は不明