Jōon 淨音 (Kennin 1 / 1201 → Bun’ei 8 / 1271), Kamakura-era Jōdoshū master, founder of the Saidani / Senjō-ji sub-line of the Seizan branch (西山禪林寺派 Seizan-Senjō-ji-ha) — i.e. the sub-school of Seizan based at Zenrin-ji 禪林寺 (popularly Eikan-dō 永觀堂) in Higashiyama, Kyoto. Signature title Saidani Jōon 西谷淨音 (“Jōon of the Western Valley”), after his sub-line designation within the Sai-no-yama / Seizan complex.
Direct disciple of 證空 Shōkū (1177–1247) at Sai-no-yama; after Shōkū’s death in 1247, Jōon succeeded to the leadership of one of the four major Seizan sub-lines (alongside the Sanjō-ke of Shōō 證入, the Saga-ke of Shōō 證圓, and the Fukakusa-ke of Ryūkū 立空). Jōon’s particular contribution was the Saidani-ryū doctrinal scheme, which read Shōkū’s kihō ichinyo and ichinen go-jō doctrines in a slightly distinct way and laid heavy emphasis on the 口決 (kuketsu — oral-transmission) tradition.
Jōon’s Saidani / Senjō-ji sub-line became the doctrinally dominant Seizan branch in late-medieval and Edo-period Kyoto, and was the matrix from which 向阿 Kōa Shōken (1265–1345) developed the vernacular trilogy Kōa sanbu KR6t0321–KR6t0323. Through Kōa’s vernacular Pure-Land writings, Jōon’s doctrinal tradition reached a lay readership that the more scholastic Sanjō and Saga sub-lines did not access.
Principal works: Kangyō myōmoku shōko jūshichi kajō 觀經名目證據十七箇條 (KR6t0333) — seventeen-article doctrinal compendium on the Contemplation Sūtra terminology; Seizan kuketsu denmitsu-shō 西山口決傳密鈔 (KR6t0334) — record of the Seizan oral-transmission. Both works are foundational Saidani sub-line documents.