Cheng Xuanying's Double Mystery Exposition 老子道德经开题序诀义疏

Composed by Cheng Xuanying, a Taoist scholar of the early Tang Dynasty, this work was recorded as a seven-volume text in both the New Book of Tang·Bibliography and the Tong Zhi·Bibliography of Arts and Literature. It was not included in the Zhengtong Daozang (Orthodox Daoist Canon).

Currently, three fragmentary Tang Dynasty Dunhuang manuscripts (P2353, S5887, P2517) survive. In addition, Cheng Xuanying’s commentary is excerpted in works such as Commentary on the Dao De Zheng Jing and Collected Commentaries on the Profound Virtue of the Dao De Zheng Jing. In modern times, Meng Wentong compiled Collated and Annotated Preface to Cheng Xuanying’s Commentary on the Laozi based on the Dunhuang manuscripts and various Daozang texts.

This work interprets the essence of the Laozi from the perspective of "Chong Xuan" (Double Mystery) philosophy, a core Taoist thought of the Tang Dynasty. It holds that the Great Dao is neither non-being nor being, yet both being and non-being—its nature is indeterminate, hence described as "huanghu" (dim and indistinct). The commentary notes: "The Dao exists everywhere, yet wherever it is, it is formless; vast and boundless, how can it have boundaries?" The Dao can generate all things and is interconnected with them: "The Dao does not depart from things, and things do not depart from the Dao. There is no thing outside the Dao, nor is there a Dao outside things. In function, it is the Dao inherent in things; in essence, it is things embodying the Dao." "The Dao and things are neither identical nor different—though different, they are one."

Furthermore, it argues that those who embody the Dao and comprehend mystery must transcend both extremes, not clinging to the view of emptiness—an idea echoing the Taoist balance of Yin and Yang. Thus, it states: "Scholars of learning cling to desires, while practitioners of the Dao linger on non-action. Though their depths differ, both suffer from attachment. To rectify these two obsessions, there is the text of 'double reduction': first reducing attachment to being, then reducing attachment to non-being—transcending both extremes to attain the middle way of non-action." It also asserts: "Those attached to being are trapped in being; those who claim to be free from attachment are still trapped in non-being. Hence, 'one mystery' is taught to transcend both attachments. Fearing scholars might cling to this mystery, 'another mystery' is expounded to dispel this subsequent obsession. Ultimately, one is not only free from attachment but also free from the freedom from attachment—this is transcending transcendence, hence the saying 'mysterious and then more mysterious'."

This encapsulates the core of "Chong Xuan" (Double Mystery) expounded throughout the work, which exerted a profound influence on the development of Taoist philosophical thought in the Tang Dynasty.