Whenever the sequences of the host periods and the visitor periods overlap entirely, the Su wen adds a small character comment “proper” (zheng $) to the character jue to indicate that in such years it is the initial period of the sequence of both the host periods and the visitor periods. However, this designation of a jue period as “proper” must not be confused with the designation of jue, zhi, shang, and so on, periods as “proper” in Su wen 70.
THE SIX QI
We now turn to the six qi (liu qi $), the second conceptual segment of the doctrine of the five periods and six qi. Similar to the way the five periods supply three conceptual levels—the annual period, the host periods, and the visitor periods—the six qi appear on three conceptual levels—the “qi controlling heaven” (si tian q—), the host qi, and the visitor qi. However, the qi controlling heaven is a more complex concept than the annual period; it refers, first, to a qi characterizing an entire year; second, to a qi characterizing the first half of a year; and third, to the six visitor qi.
For the most part, when the Su wen speaks of “six qi” apart from the context of the doctrine of the five periods and six qi, it refers to cold, summer heat, dryness, dampness, wind, and fire as causes of illness. The sequence of these six qi as causes of illness is not related to the sequence of climatic changes in the course of any given year. As is stated in Su wen 67:
When dryness dominates, then the earth is dry. When summer heat dominates, then the earth is hot. When wind dominates, then the earth moves. When dampness dominates, then the earth turns muddy. When cold dominates, then the earth cracks. When fire dominates, then the earth hardens. 20
In contrast, the “six qi” mentioned in Su wen 66 through 74 serve to characterize climatic changes in the course of one year, with these changes differing from one year to the next. They include major yang qi, cold and water; yang brilliance qi, dryness and metal; minor yang qi, minister fire; major yin qi, dampness and soil; minor yin qi, heat; and ceasing yin qi, wind and wood.
What is above in ceasing yin [years], the wind qi rules it. What is above in minor yin [years], the heat qi rules it. What is above in major yin”[years], the dampness qi rules it. What is above in minor yang [years], the minister fire rules it. What is above in yang brilliance [years], the dryness qi rules it. What is above in major yang”[years], the cold qi rules it. 21