The Xuangang Lun 玄纲论 Treatise on the Mystical Outline)

Xuangang Lun (Treatise on the Mystical Outline) is a one-scroll work compiled by the Taoist priest Wu Yun during the Kaiyuan to Dali periods of the Tang Dynasty (766–779). It was included in the Taixuan Division of the Zhengtong Daozang (Orthodox Taoist Canon). The Tongzhi·Yiwen Lue (Comprehensive Records·Outline of Arts and Literature) records Xuangang Lun as a three-scroll text, while the fifty-second entry of the Wenxian Tongkao·Jingji Kao (Comprehensive Examination of Literature·Study of Classics and Records) lists it as a one-scroll work. In the Daozang, it is divided into three parts—Upper, Middle, and Lower—comprising thirty-three chapters: the Upper Part, Ming Daode (Illuminating the Dao and Virtue), contains nine chapters; the Middle Part, Bian Fajiao (Distinguishing the Dharma and Teachings), has fifteen chapters; and the Lower Part, Xi Ningzhi (Analyzing Obsessions), includes nine chapters.

The Upper Part of Xuangang Lun reflects the author’s views on cosmogony, cultivation theory, and social-political philosophy. The Middle Part elaborates on various methods of Taoist practice from a microcosmic perspective. The Lower Part addresses worldly doubts through question-and-answer format, further expounding the ideas presented in the first two parts. The content of Xuangang Lun constitutes an important component of Wu Yun’s Taoist theories.

According to the preface to Zongxuan Ji (Collection of Ancestral Mysteries) written by Quan Deyu, a Minister of Rites in the Tang Dynasty, Wu Yun presented the three parts of Xuangang Lun to Emperor Xuanzong of Tang, who "accepted it with a gracious edict" and praised the work as a "comprehensive discourse on the wonders of the Valley Spirit." In Biography of Master Wu by Quan Deyu, it is noted that the treatise "was particularly praised by insightful scholars." This indicates that Xuangang Lun already had a certain social influence in the Tang Dynasty.

Wu Yun was one of the important scholars of the Maoshan School of Taoism in the Tang Dynasty, and his ideas were quite close to those of Sima Chengzhen. Like Sima Chengzhen’s Zuowang Lun (Treatise on Sitting in Forgetfulness), Xuangang Lun embodies the theoretical level of the Tang-dynasty Maoshan School.