Mitsusada INOUE, in his articles, 'Kodai no jotei' (The empresses in the ancient history of Japan) presented in 1964 as well as 'Kodai no kotaishi' (The crown princes in the ancient history of Japan) prepared in the same year, stated a theory that it was not the practice of the direct line succession as advocated by IWAHASHI but the practice of the legitimate child succession might have been established.
井上光貞は1964年発表の論文「古代の女帝」、同年稿の論文「古代の皇太子」で、岩橋が唱えた直系相続ではなく、嫡系相続が定められたのではないかとする説を出した。