The constitution theory of TCM is, as a doctrine, based on the theory of TCM, to research the physiological and pathological characteristics of various body constitution types, which are closely related to the nature of disease status, and disease development trends, and help guide the prevention and treatment. TCM emphasizes the characteristics of individual patients and makes an effort to research the human constitution that was generated in ancient times, and related to a large number of Chinese medicine doctrines or theories. For example, Dr. Qi Wang summarized the “Constitution Theory of TCM,” which included different physical factors with birth, age, gender, spirituality, living conditions and diet, the environment, location, disease, physical exercise, social factors, and so on, as the holistic manifestation of the whole body. The disease’s trend with pathology and incidence of illness particularly rely on the individual constitutions, and often lead to some kinds of causativeness or susceptibility to diseases. Recognition of the difference in the body constitution of the patient is the base of the principle “the same disease uses a different treatment” or “different diseases use the same treatment,” as well as the fact that the tolerance for different constitutions varies for drug reactions and acupuncture, and so on. The constitution theory of TCM also believed that analysis of the constitution should be combined with the study of Yin–Yang, Zang–Fu, Meridian theories, and explore the relationship of the eight principles and reactions of organisms. It is the fundamental (Ben, 
) as “treatment must give the fundamental solution for the root cause of the disease” (
.
Differentiation of syndromes allows TCM to distinguish disease nature from apparent disease symptoms and treat the disease’s root cause other than the symptoms. CWM emphasizes the focus of infection or the virus as the root cause. But TCM focuses on problems in the intangible system as the root cause. Qi and blood stagnation, for example, lead to damp or heat stasis, and all diseases manifest symptoms (Biao, 
), but may not reveal the essence of the disease. By getting beyond the manifestation of symptoms to the essence, and distinguishing primary from secondary aspects, the TCM emphasis is to choose a more appropriate treatment for the root of the disease.
TCM’s integrated diagnostic theories generalize the pathological changes into Yin or Yang, locations (exterior or interior), and property (cold or heat), and then rebalance non-healthy energy states (excess or deficiency). The first important recognition, though, is Yin and Yang, or the Root Cause!
Yin and Yang are of great importance in TCM. The Basic Questions says, “Yin and Yang are the law of Heaven and Earth, the outline of everything, the parents of all change, the origin of birth and destruction, and the source of all configurative force with mysteries. In the treatment of a disease, its nature and root cause must be found out” .
Each disease may have various symptoms, but just one root cause. It is difficult to treat a disease successfully without finding its root cause.