Xiao Tianzhi on the Alchemical Metaphors
The World Upside Down: Essays on Taoist Internal Alchemy, by Isabelle Robinet, page 19
The way of alchemy entirely consists of metaphors (xiang). It takes Lead and Mercury as substances, but one must know that the Essence of Lead and the Marrow of Mercury are nothing but metaphors. It is based on the terms Li ☲ and Kan ☵, but one must know that the Kan Boy and the Li Girl are nothing but empty terms. It uses the forms of the Dragon and the Tiger, but one must know that the Dragon-Fire and the Tiger-Water have no form. It talks about the "yellow sprout," the "divine water," and the "flowery pond," but these are things that can neither be seen nor used.
Source: Xiao Tianzhi (mid-13th century), in Xiuzhen shishu (Ten Books on the Cultivation of Reality), ch. 9
This is one of several translations from texts of Internal Alchemy available from the Golden Elixir website. See the complete index.