The earliest use of the term sokushin jōbutsu [attainment of buddhahood in this very body] in a T’ien-t’ai text is found in the Fa-hua wen-chii chi (T34, no.1719), Chan-jan’s subcommentary on Chih-i’s line-by-line commentary on the Lotus Sutra, the Fa-hua wen-chii (T34, no.1718). Since the term appears in Chan-jan’s discussion of the dragon king’s daughter’s realization of buddhahood, the section of the Lotus which Saichō chose as the basis of his discussion of sokushin jōbutsu, Chan-jan’s use of the term undoubtedly played a vital role in shaping Saichō’s views on the subject. Both Chih-i and Chan-jan mentioned a text entitled [P’u-sa-ch’u] t’ai-ching (T12, no.384) in their discussions of the dragon king’s daughter. In the T’ai-ching, the transformation of women into men and their subsequent realization of buddhahood, a common theme in early Mahāyāna sutras, is described. Like many of the Mahāyāna texts in which buddhahood and women are mentioned, the T’ai-ching argues against clinging to discriminations between concepts such as male and female. According to Chih-i:

The T’ai-ching states that “the women in the realms of Mara, Sakra and Brahma all neither abandoned (their old) bodies nor received (new) bodies. They all realized buddhahood with their current bodies (genshin).” Thus these verses state that the dharma nature is like a great ocean. No right or wrong is preached (within it). Ordinary people and sages are equal, without superiority or inferiority.

Chan-jan, in commenting on this passage, used the term sokushin jōbutsu to describe the realization of both the dragon king’s daughter and the women in the T’ai-ching. Saichō’s use of the term clearly was derived from Chan-jan’s subcommentary, and his discussion of sokushin jōbutsu is primarily based on the story of the dragon king’s daughter in the “Devadatta” chapter of the Lotus.