The usual theory is that the Fujiwara clan aristocrats did not want Tamehira since he was MINAMOTO no Takaaki's son-in-law, but there is also the theory that it was taken into consideration that if Tamehira, who is close in age with Reizei was selected as Crown Prince, the rule of Reizei may be too short (Michihisa HODACHI).
為平が源高明の女婿であることから、藤原氏の貴族たちに忌避されたとするのが通説であるが、冷泉と年齢の近い為平を皇太子とした場合、冷泉の在位が短期間になりすぎることに配慮したものとする説（保立道久）もある。