The idea of harmony and balance are also the basis of yin and yang. The principle that each person is governed by the opposing, but complementary forces of yin and yang, is central to all Chinese thought. It is believed to affect everything in the universe, including ourselves.

Traditionally, yin is dark, passive, feminine, cold and negative; yang is light, active, male, warm and positive. Another simpler way of looking at yin and yang is that there are two sides to everything - happy and sad, tired and energetic, cold and hot. Yin and yang are the opposites that make the whole. They cannot exist without each other and nothing is ever completely one or the other. There are varying degrees of each within everything and everybody. The tai chi symbol, shown above, illustrates how they flow into each other with a little yin always within yang and a little yang always within yin. In the world, sun and fire are yang, while earth and water are yin. Life is possible only because of the interplay between these forces. All of these forces are required for the life to exist. See the table below to understand the relationship between yin and yang.

The yin and yang is like a candle. Yin represents the wax in the candle. The flame represents the yang. Yin (wax) nourishes and supports the yang (flame). Flame needs the wax for its existence. Yang consumes yin and, in the process, burns brightly. When the wax (yin) is gone, the flame is gone too. Ying is also gone at that time. So, one can see how yin and yang depend on each other for their existence. You cannot have one without the other.

The body, mind and emotions are all subject to the influences of yin and yang. When the two opposing forces are in balance we feel good, but if one force dominates the other, it brings about an imbalance that can result in ill health.

One can compare the concept of yin and yang to the corresponding principle of tridoshas in Ayurveda, the ancient remedy from India. Ayurveda proposes that every person has vata, pitta and kapha. When these are balanced, there is the state of perfect health. When there are imbalances then there is disease.

One of the main aims of the acupuncturist is to maintain a balance of yin and yang within the whole person to prevent illness occurring and to restore existing health. Acupuncture is a yang therapy because it moves from the exterior to the interior. Herbal and nutritional therapies, on the other hand, are yin therapies, as they move from the interior throughout the body. Many of the major organs of the body are classified as yin-yang pairs that exchange healthy and unhealthy influences.

Yin and yang are also part of the eight principles of traditional Chinese medicine. The other six are: cold and heat, internal and external, deficiency and excess. These principles allow the practitioner to use yin and yang more precisely in order to bring more detail into his diagnosis.