In the Shisho 嗣書 (Certificate of Succession) volume of the Shōbōgenzō 正法眼蔵, Dōgen道元 introduces various forms of writing the shisho, Certificate of Succession, that he saw in other sects of Chan Buddhism during his journeys to Song China. Although these forms differ from the shisho of the Caodong 曹洞 sect, Dōgen recognized them as shisho. Several forms of writing the shisho existed under the Linji 臨済 sect. However, Dōgen is obscure about forms of writing shisho in the Caodong and Linji Huanglong 黄龍 sects, perhaps because these were secret teachings directly connected to himself. Furthermore, the Goyuigon kiroku 御遺言記録 mentions secret teachings transmitted between Dōgen and Ejō 懐奘 (1198–1280) only orally. However, many records of Dōgen’s studies were written later, and aspects that Dōgen and Ejō had kept unwritten were recorded by their followers Gikai 義介 (1219–1309), Keizan 瑩山 (1268–1325), and others. In the Goyuigon kiroku, forms of writing the shisho are concealed, and even when recorded in kirigami 切紙 secret documents in later generations, this awareness was passed down only with obstacles to open understanding through the use of devices such as cryptograms.
