The Eight Principles of Oriental Medicine

1. Yin / Yang
2. Cold / Hot
3. Internal / External
4. Deficiency / Excess
It is actually four principles and their opposites, but it is considered eight principles because of their opposites. Acupuncturist and Oriental Medicine practitioners use the Eight Guiding Principles to analyze and differentiate the energetic imbalances in the body or the nature of a patient’s condition. The eight guiding principles actually consist of four polar opposites: yin/yang, cold/hot, deficiency (xu)/excess (shi), and interior/external. These eight principles are the concepts used in evaluation for treatment: [1]

Yin/Yang: These principles are the generalization of the above opposites, and a condition can be categorized in terms of the relative dominance of either yin or yang. In Chinese medicine, all organisms have both yin and yang qualities and a balance of the two are necessary for good health. In general, yin energy is associated with cold, female energy, and represents the solid organs. Yang is associated with hot, male energy, and represents the hollow organs. Chronic illness is seen as yin, while acute illness is seen as yang.[2]
Cold/Hot: This principle is used to determine the overall energy of the patient. A cold condition would be one marked by a slow metabolism, chills, pale skin, and a low-grade fever, while a hot condition would be characterized by a heightened metabolism, sensations of heat in the body, high fevers, and a flushed complexion.[3]
Internal/External: This principle describes symptoms in terms of the location of the patient’s problem. External conditions are those caused by the invasion of the body by pathogens, and are usually acute and superficially located with a short duration. External symptoms are those that affect the hair, skin, muscles, joints, peripheral nerves and blood vessels. Internal conditions result from pathogens that enter the interior of the body. Internal symptoms affect the organs, deep vessels and nerves, brain, spinal cord, and bones.[4]
Deficiency/Excess: This principle describes the strength of an illness. A deficient condition would be viewed as a lack of blood (such as in anemia), energy (Qi), heat, or fluids. Chronic illness would fall in this category. An excess condition, by contrast, means that the body has too much of something, such as Qi or blood. An acute condition would be seen as an excess condition.[5]
Qi and blood (xue) are related to each other directly. Qi is the Commander (The Charioteer) of the Xue and Xue is the mother of Qi. When one is affected, they both are affected and they flow together. A patient with hot skin, a rapid strong pulse, who is suffering night sweats with a burnt smell, may have an internal yang excess condition, producing full heat. A patient with cold skin, weak pulse, and sunken eyes, may have an internal yin excess, producing full cold. The patient would be treated with cooling tonifying herbs and acupuncture needles to tonify and release some of the excess yang and heat to cool the internal body. The second patient would be treated with moxa and acupuncture and warm herbs to strength the yang and decrease the yin. This principle can also be used in personality types such as an angry person would be more yang with excess liver qi. A depressed personality type would be more yin, with excess yin and deficient yang, more internal aspects versus the external type of the yang personality.
[1] http://www.amfoundation.org/tcm.htm
[2] http://www.amfoundation.org/tcm.htm
[3] http://www.amfoundation.org/tcm.htm
[4] http://www.amfoundation.org/tcm.htm
[5] http://www.amfoundation.org/tcm.htm