The use of the expression “Jigu sanzen” 事具三千 (Three Thousand Realms Encompassed in One Thought) as a theoretical term begins in the Tendai of the Kamakura period. It was used in the meaning that all creatures possess Buddha realization.

The first use of “Jigu sanzen” in Nichiren doctrine was in Tenmoku’s 天目 Engoku jitsugishō 円極実義抄. The expression is used in the meaning “the reality aspect of the honmon 本門” (second half of the Lotus Sutra). However, it is not natural to believe that the term was used immediately after Nichiren’s 日蓮 passing.

After the Engoku jitsugishō, the expression “Jigu sanzen” is not seen until Nichiryū 日隆 (1385–1464) of the 15th century (in the Muromachi period) more than 100 years after Tenmoku. Nichiryū uses the expression often.

Perhaps Nichiryū converted the expression from a Tendai term to one of Nichiren doctrine. Therefore, we can conclude that the Engoku jitsugishō was written by a person influenced by Nichiryū in the 15th century.