The Chan thought of the Tang dynasty monk Baizhang Huaihai百丈懐海 （749-814） centered on the concept of true emptiness or śūnyatā 真空. In teaching this, he utilized the “Three Phrases” 三句 （affirmation, negation, and double negation）, then stressed transcendence even of the resulting emptiness. This was a reinterpretation of the Chan teachings of his master, Mazu Daoyi 馬祖道一 （709-788） via thoroughgoing śūnyatā thought. Baizhang’s Chan thought was inherited by his disciple Huangbo Xiyun 黄檗希運 （d. 850）, although the two masters differed in that, while both instructed their disciples to return to śūnyatā, Baizhang utilized the Three Phrases whereas Huangbo utilized the Shoulengyan jing首楞厳経 （the so-called Pseudo-Śūraṃgama-sūtra）.
