Many of the scholars who support the direct line imperial succession code theory or the legitimate child imperial succession code theory think that Fukai-no-Joten/ Fukaijoten had become a dead letter after the reign of Emperor Kanmu, and it had continued to be written according to precedent without understanding the contents.
直系・嫡系皇位継承法説を支持する学者の多くは、桓武天皇以降に不改常典は形骸化し、内容が理解されないまま先例を踏襲して書き継がれていったと考える。