The Formation of the Theory of Yin and Yang

Yin and yang was originally included in the category of the ancient philosophy of China. At first, yin and yang meant whether a place faces the sun or not. The place being exposed to the sun is yang, whereas the place not having a southern exposure is yin. The southern side of a mountain, for example, is yang, while the northern side of it is yin subsequently, through long-term living, practice and observation of every kind of natural phenomenon, people have come to realize that yin and yang, the two components which oppose each other, exist in all things, and that, furthermore, their interaction promotes the occurrence, development and transformation of things. In consequence yin and yang is used as the means of reasoning things out in analyzing all the phenomena in the natural world. "Lao Zi", a philosophical work written in ancient China, says: "All things on earth carry yin on their backs and hold yang in their arms." That is, each thing contains the two components of yin and yang. "Zhou yi", also an ancient philosophical work, draws from the complicated natural and social phenomena the same two philosophical concepts, yin and yang, whose symbols are (- -) and (-), and advocates yin and yang as the "Dao" (the basic law in the natural world) of the heaven and earth, that is, to consider the transformation of yin and yang into each other as the basic law in the universe. The impact of yin and yang theory on the science of traditioanal Chinese medicine (TCM) has promoted the formation and development of TCM's own theoretical system and, finally it, itself, becomes an important component part of the classic theory of TCM.

The Content of the Theory of Yin and Yang

The content of the theory of yin and yang can be described briefly as follows: opposition, interdependence, relative waxing and waning, and transformation.

1) Opposition and Interdependence of Yin and Yang

By the opposition of yin and yang, we mean all things and phenomena in the natural world contain the two opposite components. For example, the heaven and earth, outside and in-side, movement and stability, coming in and going out, day and night, cold and heat, rising and falling, etc., all these are opposites. In the theory of yin and yang, the heaven is considered as yang, while the earth is yin; outside is yang, while inside is yang; movement is yang, while stability is yin; going out is yang while coming in is yin; day is yang, while night is yin; heat is yang, while cold is yin; rising is yang, while falling is yin; rapid pulse is yang, while slow pulse is yin. These opposite pairs show that yin and yang exist within all things and phenomena. yin and yang not only oppose but also contain each other, without the other, neither can exist. For instance, there would be no earth without heaven1 and vice versa. Without outside, there would be no inside, and vice versa. This relationship of coexistence is known as interdepencence. TCM holds that "functional movement" belongs to yang, "nourishing substance" to yin, and that the one can not exist without the other; for example, if the intestines and other internal organs do not move, "nourishing substance" can not be digested or absorbed; and if over a long period "nourishing substances" are not provided, the organs cease to move. The book, Canon of Medicine (722-221 B.C.), says: "yin in the interior is the guardian of yang, yang in the exterior is the activator of yin". This also shows the relationship of interdependence between yin and yang.

2) The Waxing and Waning of Yin and Yang, and the Transformation between Yin and Yang

What is meant by the waxing and waning of yin and yang? Yin and yang opposing each other and yet depending on each other for existence, are not stagnant but in a dynamic state, i.e., while yin wanes, yang waxes, and vice versa. This dynamic change of succeeding each other between yin and yang is known as the waxing and waning of yin and yang. Take the seasonal climatic variations in the natural world for example. The weather gets warm when winter gives way to spring, and hot when spring gives way to summer, during which time yin wanes, while yang waxes. However, it gets cool when autumn replaces summer, and cold when winter replaces autumn in which time yang wanes, but yin waxes.

By "transformation" we mean yin and yang will transform into each other under certain conditions. For instance, in the course of suffering from a disease, the patient runs a high fever, has a red complexion, feels irritable and restless, and gets into a rapid and strong pulse condition. But all of a sudden, he feels listless, his temperature becomes lower, his face turns pale, and his pulse condition becomes so fine that the pulse is almost cut off. This is an example of transformation between yin and yang. The general law according to which things are distinguished into yin or yang is as follows. All that are hyperfunctional, excited, hot, moving, strong, bright, invisible. Light and clear, up and upwards, out and outwards, and all that have active specific characteristics belong to yang. On the contrary, all that are waning, restricted, cold, weak, dark, visible, heavy and turbid, down and downwards, in and inwards and all that have inactive specific characteristics belong to yin. It should be pointed out that the yin or yang property of things is not absolute but relative. This relativity of yin and yang is shown in the intertransformation between yin and yang mentioned above, i.e., yin may transform into yang and vice versa; it is also shown in the constant divisibility of yin and yang, i.e., either yin or yang can be still divided into another pair of yin and yang. For instance, day is of yang nature and night is of yin nature, but both day and night can be again divided like this: the period from dawn till noon is the yang aspect of yang; the period from noon till dusk is the yin aspect of yang; the period from dusk till midnight is the yin aspect of yin; the period from midnight till dawn is the yang aspect of yin.

Uses of the Theory of Yin and Yang in TCM

Yin and yang is embodied in every aspect of TCM's theoretical system. It is used to explain the tissues and structures, physiology and pathology of the human body, and direct clinical diagnosis and treatment.

1) Using Yin and Yang to Explain the Tissues and Structures of the Human Body

According to the theory of yin and yang, it is considered that opposite but unitive phenomena between yin and yang exist between rostral and caudal, inside and outside, exterior and interior, dorsal and ventral aspects of every tissue and structure of the human body. When speaking of yin and yang in the human body, the upper part is yang, the lower part yin; the exterior is yang, the interior yin; the back is yang, the abdomen yin; the lateral aspect of the extremities is yang; the medial aspect yin. When speaking of yin and yang of the internal organs in the body, the five viscera, i.e., the heart, liver, spleen, lung and kidney, are yin, because their functions of preserving vital substance tend to be stable; the six bowels organs, i.e., the gallbladder, stomach, large intestine, small intestine, urinary bladder and triple warmer, are yang, because their functions of transmit-ting and digesting water and food tend to be active. The relationship between yin and yang also remains constant among the five viscera. The heart and lung are yang, because of being higher, while the liver, spleen and kidney are yin, because of being lower. When speaking of yin and yang of every organ, the function is yang, the substance yin. When speaking of yin and yang of the channels and collaterals, the channels may be divided into channels belonging to yin and channels belonging to yang. Collaterals can also be classified as yin collaterals and yang collaterals. When speaking of yin and yang of the twelve channels, three are yang channels of the hand and three yin channel of the hand, three yang channels of the foot and three yin channels of the foot. As to the vital energy and blood, vital energy (qi) is yang, blood yin.

2) Using Yin and Yang to Explain the Physiological Function of the Human Body

TCM believes that the normal physiological functions of the human body result from the opposite, unitive and coordinate relation between yang (function) and yin (substance). Yin and yang are always in the state of dynamic balance. It is known as yin is even and well while yang is firm, hence a relative equilibrium is maintained and health is guaranteed". Physiological function is based on substance. Without substance, including the essence of life, blood, constructive energy and body fluid, there would be no source for functions. But the metabolism of substance must depend on the performance of function. If yin and yang of the human body separate from each other and can not aid each other, life will come to an end. This is what is called, in TCM, "the divorce of yin and yang means the end of one's life."

3) Using Yin and Yang to Explain the Pathological Changes of the Human Body

In TCM, it is thought that the imbalance of yin and yang is one of the basic pathogeneses of a disease. For example, preponderance of yang leads to hyperfunction of the organism and heat manifestations, while preponderance of yin hypofunction of the organism or endogenous cold. Deficiency of yang brings on symptoms of external cold, while deficiency of yin as the result of exhausted vital essence leads to endogenous heat. Yang in excess makes yin suffer, while yin in excess makes yang suffer. In severe damage of yang, yin is involved, in severe damage of yin, yang is involved, too. Thus, yin and yang are both damaged. A case of yin nature (hypofunction) in its extreme may show yang (hyperfunction) symptoms and signs, while a case of yang nature (hyperfunction) in its extreme will give rise to yin (hypo-function) symptoms and signs.

4) Using Yin and Yang to Diagnose and Treat Diseases

Because one of the basic pathogeneses of a disease is the imbalance of yin and yang, any disease, no matter how intricate and volatile its clinical manifestations, can be diagnosed with the theory of yin and yang. Although diseases are classified as exterior and interior according to their locations, and as cold, heat, asthenia and sthenia according to their nature, if the theory of yin and yang is used, the types of exterior, heat and sthenia are yang; interior, cold and asthenia yin. In TCM, in making a diagnosis, the first important thing is to ascertain whether the disease is yin or yang. For example in observation of the patients' complexion, those who look bright are patients of the yang character, while those who look dark and gloomy are patients of the yin character. In listening and smelling, those who have a loud and clear voice have a yang character, while those who have a low and weak voice a yin character. In inquiring, those who have a fever, feel thirsty, suffer from constipation and have a rapid pulse condition are of yang, while those who have an aversion to cold, don't feel thirsty, have loose stools and a slow pulse condition are of yin. In pulse feeling and palpation, those whose pulses are floating, rapid, large, slippery and full are of yang, while those whose pulses are deep, slow, small, rough and empty are of yin. How is the theory of yin and yang used in treating diseases in TCM? Preponderance of yang leads to hyperfunction of the organism and heat manifestations, which is known as sthenic heat syndrome. In treating sthenic heat syndrome, drugs of cold and cool nature should be used in order to inhibit the preponderance of yang, i.e., heat syndrome must be treated with drugs cold in nature. Preponderance of yin leads to hypofunction of the organism or endogenous cold that is called cold-sthenia syndrome. In treating it, drugs of a warm-heat nature should be used so as to restrict the predominance of yin, i.e., cold syndrome should be treated with drugs warm in property. The deficiency of yang brings on symptoms of external cold, which are called deficiency-cold syndrome. In treating it, drugs of warm and invigorating nature should be used. This is known as treating the hyperactivity of yin by supplementing yang, the source of fire. The deficiency of yin as a result of exhausted vital essence leads to endogenous heat, which is called as asthenic heat syndrome. In treating it drugs of nourishing yin should be used. Thi5 is what is known, in TCM, as replenishing the vital essence, (especially that of the kidney and liver) to check virtual yang (exuberance of the vital function) caused by the deficiency of yin factor. In treating those diseases in which there is severe damage of yang, yin is involved, although the first thing is to reinforce the vital function, yet, the vital essence, at the same time, should be also invigorated. In treating those diseases in which there is severe damage of yin, yang is involved, while the vital essence is being replenished, the vital function should be strengthened, too. In treating those diseases resulting from the deficiency of both yin and yang, both the vital essence and the vital function should be replenished. The property, flavor and function of Chinese medicinal herbs can also be summarized in the light of the yin and yang theory, and this forms a basis for the clinical application of Chinese medicinal herbs. For example, the herbs of cold and cool nature belong to yin; while the herbs warm and hot in nature, yang. The herbs with sour, bitter and salty flavors belong to yin, while the herbs with pungent, sweet and bland flavors, yang. The herbs with astringent and subsiding function belong to yin, while the herbs with dispersing, ascending and floating function, yang. In TCM, the principles of treatment are established just on the basis of the predominance or weakness of yin and yang. Once the principle is established, herbs are selected according to their property of yin and yang and their function. In so doing, one can achieve the aim of curing diseases.