In the old days it was believed that Emperor Uda came to power due to his strict Buddhist belief; however, one recent theory says the reason was that dominant political control had been taken away from the Fujiwara clan, or that it was done to stop the complaints from the royal families after Emperor Uda came into power by coming back to the Imperial Family, although he had become an allegiant (as indicated by the retired Emperor Yozei in his remark in "Okagami (The Great Mirror)," which is described below).
天皇の譲位については古くは仏道専心説が有力であったが、近年では藤原氏からの政治的自由を確保するためとする説、一旦臣下から皇族に復帰して即位したためにこれに不満を抱く他の皇族の皇位要求の動きに先んじた説などがある（後述の『大鏡』の陽成上皇の発言はその暗示ともされる）。