It is a commonplace that the Han dynasty distinctions between the 100 schools of philosophy are to some extent false divisions forced on a much more complex history. Lewis takes this further and tries to uncover what the categories of thought were in Han and pre-Han China. Part of this, particularly in Writing and Authority, is the importance of patterns. There are patterns that govern the changes in the universe, human affairs and the body, and understanding and adjusting and adjusting to these patterns is what knowledge is all about. (Lewis explains all this a lot better than I do.)

One aspect of this is the sage, the person who has learned to be a master of patterns. There are lots of different aspects of this, one of which is medicine. One’s body is of course governed by the same patterns as everything else and thus being a doctor, preserving one’s health and attaining immortality through alchemy and ruling the empire all involve the same sort of knowledge. Those with a proper knowledge of patterns can avoid all sorts of nasty things and can also draw power from the universe.

In the history of science, alchemy refers to both an early form of the investigation of nature and an early philosophical and spiritual discipline, both combining elements of chemistry, metallurgy, physics, medicine, astrology, semiotics, mysticism, spiritualism, and art all as parts of one greater force. Alchemy has been practiced in Mesopotamia, Ancient Egypt, Persia, India, and China, in Classical Greece and Rome, in Muslim civilization, and then in Europe up to the 19th century—in a complex network of schools and philosophical systems spanning at least 2500 years.

Western alchemy has always been closely connected with Hermeticism, a philosophical and spiritual system that traces its roots to Hermes Trismegistus, a syncretic Egyptian-Greek deity and legendary alchemist. These two disciplines influenced the birth of Rosicrucianism, an important esoteric movement of the seventeenth century. In the course of the early modern period, mainstream alchemy evolved into modern chemistry.

Today the discipline is of interest mainly to historians of science and philosophy, and for its mystic, esoteric, and artistic aspects. Nevertheless, alchemy was one of the main precursors of modern sciences, and many substances and processes of ancient alchemy continue to be the mainstay of modern chemical and metallurgical industries.