Sadaie developed the idea of Yugen (subtle and profound beauty) or Ushin, which was advocated by his father Toshinari, and established 'suggestiveness and fascinating style,' being greatly reflected in the collected poems.
定家の父俊成によって提唱された幽玄、有心の概念を、定家が発展させて「余情妖艶の体」を築き上げ、これが撰歌に大きく反映されている。