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The key to treatment lies in the appropriateness of the prescription and medicine, which depends on the proper combination of Qi (Vital Energy) and Flavor. The Ancient Sages established plumb lines and squares to measure straightness and crookedness, while later philosophers created compasses and set-squares to define circles and squares.

However, the generation of all things necessarily relies on Heaven (Time/Cosmic influences), and their maturation necessarily depends on Earth (Material/Substance). Therefore, what has form belongs to Flavor, and what is formless belongs to Qi. Qi is Yang, and Flavor is Yin. Yang Qi exits through the upper orifices (such as the mouth and nose), while Yin Flavor exits through the lower orifices (the urethra and anus). When Qi transforms, Essence (Jing) is generated; when Flavor transforms, Form (Xing) grows. Thus, products of the Earth nourish Form; for those with deficient Form, tonification should be done with Qi. Products of Heaven nourish Essence; for those with deficient Essence, tonification should be done with Flavor. Hence, Qi belongs to Heaven. There are four types of Qi: Warm and Hot belong to the Yang of Heaven, while Cold and Cool belong to the Yin of Heaven. Yang ascends, and Yin descends. Flavor belongs to Earth. There are six types of Flavor: Pungent, Sweet, and Bland belong to the Yang of Earth, while Sour, Bitter, and Cold belong to the Yin of Earth. Yang floats, and Yin sinks.

In prescribing, one may use Qi alone, Flavor alone, both Qi and Flavor together, first Qi then Flavor, or first Flavor then Qi. Furthermore, selection may be based on image/symbolism, color, or intent, so one cannot rigidly adhere to a single method. A single herb may possess two or three flavors, or one or two Qi properties. If there are many Heat-natured herbs and few Cold-natured ones, the overall nature will not be Cold; if there are many Cold-natured herbs and few Heat-natured ones, the overall nature will not be Heat. Two parts Cold and one part Heat may result in a Warm nature; more Warm than Heat results in a Hot nature; more Cool than Cold results in a Cold nature. One cannot rely on a single pathway for selection. Additionally, if a mixture is half Cold and half Heat, taking it during the day causes it to ascend following the Heat category; taking it at night causes it to descend following the Cold category. On sunny days, it follows Heat; on rainy or cloudy days, it follows Cold. Because the categories followed vary, the changes are diverse.

However, Sour and Salty flavors do not have ascending properties, while Pungent and Sweet flavors do not have descending properties. Cold substances do not float, and Hot substances do not sink; this is their inherent nature. To make an ascending agent descend, it must be restrained; to make a sinking agent float, it must be carried. Pungent disperses, and its movement is horizontal; Sweet moderates, and its movement is upward; Bitter drains, and its movement is downward; Sour astringes, and its nature is contracting; Salty softens hardness, and its nature is relaxing. The differences in vertical (up/down), expansion/contraction, and horizontal movement are thus manifested.

Regarding the nature of Heat medicines, when they damage the human body, they inevitably cause hyperactivity and usurpation (excessive rising), because Fire's nature is to blaze upward. Regarding the nature of Cold medicines, when they damage the human body, they inevitably cause flooding and overflow, because Water's nature is to moisten and flow downward. It is logically impossible for a substance to avoid both hyperactivity/usurpation and flooding/overflow, yet exclusively damage the Harmonious Qi (Chonghe Zhi Qi) of the Middle Jiao.