Classic of Triune Unity Zhouyi Cantong Qi 周易参同契

Referred to in short as Cantong Qi.

Compiled by Wei Boyang, an alchemist of the Eastern Han Dynasty, it was roughly written between the reigns of Emperor Shun and Emperor Huan of the Han Dynasty (126–167 AD). Ge Hong first mentioned in Shenxian Zhuan (Biographies of Immortals): "Wei Boyang wrote Cantong Qi Wuxing Xianglei (Cantong Qi: The Correlation of the Five Elements) in three volumes.

Classic of Triune Unity

 Its discourse appears to explain the Zhouyi (I Ching), yet it actually borrows the concepts of hexagram images to elaborate on the principles of alchemy." The book is divided into three parts: the upper, middle and lower volumes. For the most part, it assimilates the Huang-Lao thought prevalent in the Han Dynasty and the principles of image-numberology in the Zhouyi to expound the way of cultivating immortality and practicing alchemy. It integrates and harmonizes the theories of three schools—the "Great Changes" (Zhouyi), "Huang-Lao" and "Alchemy"—hence the name Cantong Qi (The Unification of the Three Essentials). The author holds that the practice of alchemy follows the same path as the creation and transformation of heaven and earth; the generation and evolution of all things in the world result from the waxing and waning of yin and yang, the intercourse of Kan and Li (symbolizing dragon and tiger), and the circulation of Qi. Therefore, those who pursue immortality through alchemy must also grasp the principles of the waxing and waning of yin and yang, the mutual generation and restriction of five elements, and the changes of hexagrams and lines when conducting alchemical experiments in the furnace. Thus, the book’s discourse on the ebb and flow of fire and the refinement process in alchemy is all based on the theories popular in the Han Dynasty, including the Guiyi (Applying the Heavenly Stems to Hexagrams) theory, the Twelve Xiao Xi (Twelve Hexagrams of the Waxing and Waning of Yin and Yang) theory and the Liu Jia Gu Xu (The Vacancies of the Six Jia Cycles) theory. Later generations have offered different interpretations of its alchemical methods: some regard it as internal alchemy, some as external alchemy, and others as a combination of both, with the internal alchemy interpretation being more prevalent. As the earliest existing work on alchemical principles, it exerted a profound influence on later generations and was revered by followers of Taoism as the "Ancestor of Alchemical Classics". Since the Sui and Tang dynasties, numerous commentaries have been written on this book. Currently, eight annotated versions of Cantong Qi are included in the Taixuan Section of The Daozang. Among them, Zhouyi Cantong Qi Fenzhang Tongzhen Yi (Annotated Explanation of the True Meaning of the Zhouyi Cantong Qi by Chapters) compiled by Peng Xiao of Later Shu is generally considered the most reliable. See the corresponding entry for details.