of the Five Periods and Six Qi in the Su wen
The doctrine of the five periods (wu yun $) and six qi (liu qi $) is outlined in the Su wen in seven “comprehensive discourses” (da lun $). 1 These are treatises 66 through 74 (not counting the two apocryphal treatises 72 and 73), comprising about one-third of the entire text of the Su wen. The origin of the notions outlined in these treatises is unclear; no parallel literary sources outside the Su wen are known that could be used to date the early development of these thoughts. For the time being, all that can be said is that treatises 66 through 74 form a section of the Su wen that is conceptually rather separate from the remaining two-thirds of the text. That the “seven comprehensive discourses” include commentaries by Wang Bing provides a date ante quem for their compilation, namely, the eighth century. From a statement in the preface to his Su wen edition it must be concluded that this section was added to the text by Wang Bing himself.
The doctrine of the five periods and six qi explains relationships ancient Chinese observers assumed to exist between climate and a broad range of natural phenomena, including human health and illness. Apparently the concepts of the five periods and of the six qi were introduced to distinguish among and specify climatic characteristics of well-defined time periods. By drawing on notions of a cyclical recurrence of calendrical terms and by adopting the doctrines of yin-yang and of the five agents, an attempt was made to order what may at first glance appear to be disorder, namely, the occurrence of rain and wind, dryness, cold, and heat in the course of the four seasons and over the years.