Thus, when applying differentiation of syndrome according to the eight principles, physicians are required not only to have a masterly cotmrmand of the characteristics of each syndrome, but also to pay attention to their coexisting, interlacing, transforning, and true or false conditions, so and so only can the disease be understood in an all-round way. Thereby, providing reliable basis for treatment.

Yin and yang are a pair of principles used to summarize the other three pairs of principles and are also the key principles in the eight principles. So the other three pairs of principles are classified under either yin or yang. Exterior, heat and excess syndrones are classified into the category of yang, while interior, cold and deficiency syndromes fall into the category of yin. Yin syndrome is characterized by deficiency of yang -qi and excess of yin in the body. Yang syndrome is characterized by the hyperaсtivity of yang-qi and hyperfunctions of the zang fu-organs, resulting from excess of yang -heat in the body. Yin and yang are also used to explain the pathological changes of the zang-fu organs. e.g. yin depletion, yang depletion, yin deficiency and yang deficiency, etc.

Differentiation of syndromes according to the theory of qi, blood and body fluid is a differentiating method to analyse and identify the pathological changes of qi, blood and body fluid according to the theory of qi, blood and body fluid. Qi, blood, and body fluid, are the material basis for the functional activities of the zang-fu organs,.their formation and circulation depend upon the normal functions of the zang- fu organs. Therefore the pathological changes of qi, blood and body fluid msy bring about the dysfunction of the zang-fu organs, and the dysfunction of the zang- fu organs will be bound to cause the pathological changes of qi, blood and body fluid. Hence, both of then should closely coordinste and complement each other.. Qi bas many syndromes, which are usually classified into four classes: qi deficiency, qi sinking, qi stagnation and reversed flow of qi. As concerns blood syndromes, TCM tends to group thern under four heads: blood deficiency, blood stasis, heat in blood and cold in blood." Physiologically, they complement each other and, pathologically, affect each other. Thereby, forming differentiation of syndrones of the same disease of qi and blood. Clinically, there is qi stagnation and blood stasis, qi deficiency and blood loss, deficiency of both qi and blood, qi deficiency and blood stasis, and qi prostration resulting from hemorrhage. Syndromes of body fluid,may be classified into two categories: insufficiency of body fluid and water retention.

Insufficiency of body fluid may cause the clinical manifestations: dryness of the mouth and throat, dry lips and tongue, subsidence of eyes, dry skin, scanty urine, constipation, a red tongue with scanty saliva and thready, rapid pulse. Whereas, retention of water may form such pathological substances as water, dampness and phlegm retention. Usually seen in edema, tympanites and phlegm-retention.