The Eight Principles form the basis for diagnosing illness in traditional Chinese medicine. The principles are based on four dualities: internal/external, cold/heat, deficiency/excess and yin/yang. Practitioners of this art use these dualities to determine the type of illness a patient has and the best way to treat it. Before the recognition of germ theory and disease, this was the only kind of healing science available to much of Asia. Many people still use traditional Chinese medicine as an alternative or supplement to modern medicine.
The first diagnostic principles, internal and external, are fairly straightforward. External conditions occur on or near the surface of the body and involve the skin and muscles. Illnesses such as colds and the flu, which cause fever and other outer symptoms, are said to be external and manifest from outside influences. Internal illnesses are considered more serious and affect the core of the body. These illnesses are thought to be the result of a problem with the “zang-fu” organs.
The second set of Eight Principles is organized around the effects of temperature on the body. Cold illness causes slow movements, body aches and chills. Clear or white bodily discharges are considered to be signs of cold. Hot illness is related to fever or thirst and produces thick discharges from the body.
The third diagnostic principles are deficiency and excess, or xu and shi, as they are known in Chinese. Xu diseases are caused by a deficiency or lack of something within the body and manifest themselves through weakness and lethargy. Shi diseases come from an internal excess and produce acute symptoms that come and go quickly.
Yin and yang are the fourth and final pair of Eight Principles. These govern the other six and form the conceptual basis for much of Chinese philosophy. The yin is associated with internal, cold and xu conditions that are chronic, slow-moving illness. Traditional practitioners will prescribe heat and strengthening herbs to cure a person with a yin condition.
Yang illnesses are characterized by heat and excess and are internal ailments. These are acute conditions, often causing sharp pain, that come on a patient quickly. Treatment of these diseases involves keeping the patient cool and well hydrated.
The Eight Principles appear in many aspects of traditional Chinese medicine. Practitioners of acupuncture and herbal medicine use these principles to diagnose conditions and attempt to bring the Yin and Yang back into harmony. Many adherents of these practices also use these principles to guide their diet and lifestyle choices.