The existing Yoro Ritsuryo Code stipulated in its provisions of Denryo (rice field law) Article 5, Article of Koden, that those who did meritorious deeds would be divided into four classes of Daiko, Joko, Chuko, and Geko according to the degree of their achievements from top to bottom, and that Daiko would be granted inheritance of their Koden generation to generation forever, Joko for three generations (down to great-grandchildren), Chuko for two generations (down to grandchildren), and Geko only to their children.
現存する養老律令の田令第5条（功田条）では、功績の大きさによって勲功者を大功・上功・中功・下功の四等に区分した上で、大功は功田を永久に世襲、上功は3世（曾孫）まで相続、中功は2世（孫）まで相続、下功は子まで相続、と各区分ごとに相続できる子孫の範囲が定められていた。