Four qi refers to four different medicinal properties of drugs, namely cold, hot, warm and cool, also known as four properties. Cold and warm are two opposite medicinal properties; There are differences in degree between cold and cold, and between heat and temperature, that is to say, the medicinal properties are the same, but there are differences in degree, and temperature is second to heat and cool to cold.

Because there are procedural differences between cold, cool and hot temperatures, we should also pay attention to them when using drugs. If warm medicine is used instead of hot medicine, and cold medicine is used instead of cold medicine, the seriously ill medicine can not achieve the purpose of curing the disease; On the contrary, when warm drugs are used and hot drugs are used, the yin will be hurt, and when cold drugs are used instead of cold drugs, the yang will be vulnerable.

Four gas division

One is the five-point method. Li Shizhen put forward the classification of five natures, saying that "five natures are ambiguous, cold, hot, warm, cool and flat";

The second is the quartering method. Shennong's Classic of Materia Medica puts forward that medicine "has four qi: cold, hot, warm and cool", which is followed by later generations.

The third is the dichotomy. Six Books of the Tang Dynasty put forward the theory of "three natures", saying that "three natures are cold, warm and flat";

The fourth is dichotomy. As far as specific drugs are concerned, there are still differences between cold and hot, which belong to cold and hot.