There had been something like soi, but in 760, Denbo-I and Shugyo-I were placed under Daihossi-I, and four types of ikai (Hosshi-I, 満位, 住位, and 入位) were placed respectively under Denbo-I and Shugyo-I.
以前から僧位らしいものはあったが、760年（天平宝字4年）大法師位のもとに伝法位と修行位がおかれ、伝法位と修行位とにそれぞれ法師位、満位、住位、入位の4種の位階が置かれた。