In one theory, the origin of this term "Kanso" is said as a simplified form of official Soji, and in another theory, it is said to have originated in a formalization of casual Sojo (a report to the Emperor) not based on Kushiki Ryo (the law concerning official documentary forms of state affairs).
その由来については本来の形式である奏事を簡略化して成立したとする説と公式令に拠らない略式の奏上が公式化したものとする見方がある。