The most widely-accepted theory is the direct line imperial succession code theory that Koyata IWASAKI presented in 1951 in his article 'The permanent code established by his majesty Emperor Tenchi,' in which he argues that this is the law that determinates the imperial succession rule, eliminating collateral successions between brothers.
歴史学者の間で最も有力なものは1951年に岩橋小弥太が論文「天智天皇の立て給ひし常の典」で提唱した直系皇位継承法説で、兄弟継承を排して天皇の子への皇位継承を定めた法だとするものである。