Four Images Time Model: The Law of Mutual Inclusion of Yin and Yang

A pure binary division into Yin and Yang is orderly, but within the continuous flow of time, transitional states must exist as things move between Yin and Yang. This gives rise to the Four Images time model. The essence of the Four Images is the law of mutual inclusion of Yin and Yang: Shaoyang (Yang within Yin), Taiyang (Yang within Yang), Shaoyin (Yin within Yang), and Taiyin (Yin within Yin). It is a higher-order tool in Chinese medicine for capturing dynamic turning points in time. It can also be understood as dividing a complete cycle into four phase intervals.

As time unfolds, yang qi does not appear all at once. It passes through a cycle of Yang arising within Yin (spring/dawn) → Yang at maximum abundance (summer/noon) → Yin arising within Yang (autumn/dusk) → Yin at maximum abundance (winter/midnight). When classical texts use expressions such as “Yang within Yin” or “Yang within Yang,” they are referring to this Four Images model. Here, corresponding phase intervals in revolution and rotation are described together to emphasize how the same set of energetic symbols can be used flexibly across different temporal scales.

The Four Images model is used in the “Great Treatise on Regulating the Spirit in Accordance with the Four Qi” of the Huangdi Neijing to guide daily routines. For example, the winter (Taiyin) principle of “going to bed early and rising late” uses the annual-scale Four Images cycle to align and guide the daily-scale cycle of rest. A personal bad habit of the website’s author is drinking coffee in the afternoon. After dusk, the external time has entered Shaoyin (Yin within Yang), when bodily activity should slow and cool as it approaches evening. Drinking coffee then is likened to forcibly “lighting a Taiyang” inside the body—an action presented as strongly contrary to the temporal pattern of the Four Images.