Which Taoist alchemical text is known as the 'Kinship of the Three'?

Which Taoist alchemical text is known as the “Kinship of the Three”? Cantong Qi is the Taoist alchemical text known as the “Kinship of the Three.”

Its fuller title is Zhouyi Cantong Qi, commonly translated as “The Kinship of the Three in Accordance with the Book of Changes.” The text is traditionally attributed to Wei Boyang, a semi-legendary alchemist of the Eastern Han period, and is often dated to around the second century CE.

The work brings together three major strands: the cosmology of the Book of Changes, Taoist ideas about the Dao and non-action, and alchemical transformation. Its imagery includes yin and yang, the trigrams Qian and Kun, and the symbolic pairing of lead and mercury.

Cantong Qi became especially influential in later Taoist internal alchemy, or neidan, where laboratory substances and operations could also represent transformations of the body and spirit. It is sometimes confused with Baopuzi, another important alchemical work, or with the similarly named Buddhist Cantongqi, a Zen poem. “Kinship of the Three” is a translation of the title, not a separate text.