Most likely you have heard of Yin and Yang but have a very vague idea of what they mean. In
a nutshell, yin and yang are complimentary aspects of everything that exists. In nature, everything hastwo opposing or complimentary aspects, such as day and night, sunny side and shady side, hot and cold, the sun and moon, top and bottom, left and right or front and back. The Chinese characters 陰陽 yin and yang in themselves literally mean the moon and the sun, or shady and sunny. When applied to the body, the yin-yang pairs are: inside – outside, lower - upper, back - front, interior – exterior, Jong – Fu, blood – qi, cold – hot and cool – warm. Yin and yang are meaningful only in relation to each other, much less so in absolute terms.
These complementary pairs of opposites are governed by the law of unity, which states that they act to oppose each other but are mutually dependent. Yin and yang need to be considered in relative terms, not in isolation.
In Chinese medicine, yin and yang must be considered together and not in isolation. This concept makes Chinese medicine holistic in that the entire picture is taken into account. For example, male impotence is caused by kidney yang deficiency, but the treatment must begin with the nourishment of kidney yin.
Other important aspects of yin and yang are that they are opposing, rooted in each other and they transform into each other. The opposing nature is not hard to understand, since they exist almost always in a complementary pair. To say that yin and yang are rooted in each other is referring to the mutual dependency. For example, for yang to be able to protect the body, yin has to be strong inside. Another example is the relationship between qi and blood. When yin is deficient, the symptoms of excessive yang appear, such as bad breath, dry mouth, tooth ache, red eyes etc.. The transformation between yin and yang occurs when one of them is either deficient or excessive over time, the condition reverses. For example, patients experiencing fever over a long period of time will feel chills.