Introduction

Yin and Yang are concepts difficult to translate from the Chinese language, but of great importance in Chinese philosophy and medicine. Their Chinese characters allude to a mountain with a sunny side and another covered by shadows:

• Yin means "dark or shady side of a hill".
• Yang "sunny side of the hill".

Light and shadow, day and night, are the duality that exists in everything we see. Two contradictory parts of every phenomenon that relate to each other mutually. Dividing nature into Yin-Yang is an effort of human beings to understand it and understand themselves within it without attempting to control or subdue it, on the contrary, acting in harmony with its changes.

It is this division of reality that gives way to the 10,000 things or beings. Light, immaterial, symbol of Yang, condenses or contracts until forming a particle, symbol of Yin. When this particle expands it becomes light again. Thus it constantly mutates, giving cyclicity and movement to the universe. The nature of both phenomena can never be absolute, but rather relative, and their existence is always determined by internal or external conditions. Everything contains these two polarities, which in certain circumstances transform into each other mutually and at the same time exist in the depths of their opposite. This is a cycle that never ends. From its observation have been extracted the four laws of Yin and Yang.

In the beginning, as in gestation, the human being has no consciousness of separation (1). When this consciousness appears in bodily experience is when the same human being turns towards itself and for the first time lives in reference to other beings (2). Thus Yin-Yang as philosophical thought comes from bodily experience. The theory of Yin Yang is applied to nature, ethics, astrology, medicine and social order.

Application of Yin Yang theory to Traditional Chinese Medicine

To understand how the theory of Yin and Yang is applied to Traditional Chinese Medicine, it is necessary to understand Yin - Yang especially with respect to zones and structures of the body and to understand the four laws of Yin - Yang with respect to bodily functions and symptoms and pathological expressions.

• The four laws of Yin and Yang in Traditional Chinese Medicine.
• Bodily structures and Yin - Yang.
• Differentiation of symptoms according to Yin - Yang.
• Imbalances between Yin - Yang.

In Traditional Chinese Medicine, both diagnosis, physiology, pathology and treatment can be reduced to the theory of Yin - Yang. From this duality everything starts in the macrocosm and the human body as microcosm is a reflection that can be observed through this prism. There is no Chinese medicine without Yin - Yang, all physiological processes, signs and symptoms can be analyzed in light of this theory. In essence, there are four strategies that reduce all treatment:

• Tonify Yin.
• Tonify Yang.
• Drain Yin.
• Drain Yang.