In TCM, Yin and Yang are the key factors constituting the syndrome. The Yin–Yang theory is prominent among the eight principles. The TCM syndrome without Yin–Yang is basically nonexistent. But the Yin and the Yang are not equivalent, Yang is the commander of Yin, and Yin is the subordinate of Yang. The Yin–Yang theory reveals a basic law that the whole determines the part. For the interaction of the human body with nature, the existence of the human being is based on its adaptation to nature. If the human body cannot quickly attain a balance with nature, diseases often come along because of conflict between the part of the body and the entire body or between the tissue cells in an organ and their internal environment. The disease will be expressed as an “excess syndrome” if the conflict is caused mainly by an irregular change of the outside world, whereas the disease will be expressed as a “deficiency syndrome” if the conflict is caused by the accumulation of some cells that have not adapted to the internal environment. Similarly, the disease can be considered an “exterior syndrome” if the conflict is mainly induced from the outside to the inside, and an “interior syndrome” if it is mainly induced from the interior to the exterior.
The human body is a holistic system connected through the meridian system, a main channel in the continuous water environment within the human body. Transportation of matter and information depends on water molecules. Therefore, the functional state of the entire body is subject to the actual characteristics of the water molecules, such as the amount of free hydrogen protons in this environment. If the properties are favorable for the transportation of both matter and information, the local information would be quickly sent to the brain, and the processed information would be sent to every part of the body as assisted by the asymmetrical supply of blood. The entire body would be in a proper circulation state. However, this is just a theoretical model. If the amount of free hydrogen protons is excessive in the environment, the metabolism would be in disorder and the “heat syndrome” would dominate the functional states, even though the transmission rate of the information is still high. On the other hand, if the amount of free hydrogen protons in the environment is insufficient, the metabolism of the entire body and the circulation of the energy would slow down, and consequently reduce the transmission of information. In the latter case, the human body cannot rapidly adapt to the environmental changes. This is a typical functional state of the “cold syndrome.” Similarly, the “asthenia symptom” is characterized by insufficient energy of the partial tissue cells. It in turn cannot adapt to the change of the internal environment. The asthenia symptom is characterized by partial energy stasis with overexcited (active) tissue cells. Because the syndrome is too sensitive to the change of the entire body, it cannot be counteractive to the entire body in an imbalanced state. Through the comprehension of the Eight Principles, the syndrome in TCM is an extremely complicated concept. It includes a series of disease symptoms as well as causes of disease, locations, pathological changes, and trends of disease development.