Busshō (Japanese: 佛性), or Buddha Nature, is the third book of the Shōbōgenzō by the 13th century Sōtō Zen monk Eihei Dōgen.
As the title implies, the work is a discussion of the concept of buddha nature, laying out Dōgen's unique viewpoint on what the term means.
He presents this thesis in his characteristically difficult style using frequent allusions to and comments on classical Zen literature, as well as complex word play hinging on creative interpretations of Classical Chinese sentence structure.
[1] The literature of Mahāyāna Buddhism includes many discussions and comments on the notion of buddha nature, and its exact meaning has been interpreted in numerous ways over many centuries.
He then equates this statement to a dialogue Dōgen often cites between Nanyue Huairang and his teacher Dajian Huineng in which they discuss the undefiled nature of "practice and verification" (Japanese: 修證; shushō), setting up his argument that buddha nature is just reality itself.