The Applications of Yin-Yang Theory in TCM
1. Explaining the Structure of the Body
In explaining the body's structure by the yin-yang theory, the human body is regarded as an organic whole of the unity of opposites. The structure can be divided into two mutual opposite parts of yin and yang, which are related to each other and cooperate closely. Thus, Chapter 25 of Plain Questions states, "That the human life has its figure cannot be separated from yin and yang. "
The portions of the human body break down as follows: the exterior is yang and the interior is yin; the back is yang and the abdomen is yin; the head is yang and the foot is yin; and the body surface is yang, and the internal organs are yin. Regarding the body surface, the skin is yang and the muscle, tendon, and bone are yin. Among the viscera,the six fu-viscera are yang, and the five zang-viscera are yin. Among the five zang-viseera, the heart and liver are yang, and the lung, spleen, and kidney are yin. In addition,each of the viscera also can be divided into yin and yang. For example, the heart can be subdivided into heart-yang and heart-yin; the kidney into kidney-yang and kidney-yin;and the stomach into stomach-yang and stomach-yin.
As regards the meridians, those travelling in the lateral aspects of limbs and the back are yang (such as the three yang meridians of the hand and foot, with the exception of the Foot Yangming Meridian), while the meridians travelling in the medial aspects of limbs and the abdomen are yin (such as the three yin meridians of the hand and foot).
However, it should be pointed out that the properties of yin or yang of the different parts, structures, and organs are not absolute, but relative. They may vary according to changes in certain conditions, and depending upon the relationship being considered. For example, when considering the relationship between the back and chest, the back pertains to yang while the chest pertains to yin. Similarly, in classifying the five zang-viscera according to the superior-inferior relationship, the heart and lung pertain to yang because of their location above the diaphragm, and the liver, spleen, and kidney, located below the diaphragm, pertain to yin. In sum, the yin and yang of the portion, tissues,and structure of the body are merely the general classifications for their relative properties.
2. Explaining Physiology of the Body
It is held by TCM that the human body's normal life activities are the result of unification of opposites, and the coordination and balance between the two aspects of yin and yang. On the one hand, the human body's physiological functions are manifested in the organism's entire protective function, which attempts to prevent attack from exogenous evils. One the other hand, they also are manifested in the functional activities of viscera and structure.
Yang in the exterior acts as the exterior-protecting function to protect the body's internal organs, while yin (the material basis of yang) remains in the interior to store and provide energy for yang constantly. Thus, Chapter 5 in Plain Questions states: "Yin remains inside as the guard for yang, while yang remains outside as the envoy for yin. " It also is said in Chapter 3, "The so-called yin is to store essence and provide qi, and the yang is to protect the exterior for consolidation. "
The five zang-viscera pertain to yin because they store the essential qi, while the six fu-viscera pertain to yang because they can digest and transport food. But there are yin and yang in each viscus. All of the functional activities pertain to yang and all of the organs and nutrient materials that produce functional activities pertain to yin. For example,the heart has the functions of promoting blood circulation and of dominating the activities of mind, consciousness, and thought, which pertain to yang, while heart-blood and the organ of heart pertain to yin. The liver has the functions of regulating the blood quantity,the mind, and emotions, which pertain to yang, while liver-blood and the organ of liver pertain to yin. Likewise, the spleen has the functions of transporting and transforming food, distributing food essence, and commanding blood circulation, which pertain to
yang, while spleen-fluid and the organ of the spleen pertain to yin. The lung has the functions of dominating qi, controlling breath, and aiding the heart in promoting blood circulation, which pertain to yang, while lung-fluid and the organ Of the lung pertain to yin. Finally, the kidney has the functions of storing the essence, producing marrow,dominating reproduction and development, and controlling water metabolism, which pertain to yang, while the kidney-essence and the organ of the kidney pertain to yin. It is the same for the six fu-viscera. Their functions pertain to yang while the organ of each fu-viscus pertains to yin.
The yin-yang relationship of the body's physiological functions serves mainly to maintain their coordination and balance. For instance, the body's excited function pertains to yang and the depressed function pertains to yin; the hyperfunction pertains to yang and the hypofunction to yin. To the physiological activities, the excited and depressed, and the hyperfunction and the hypofunction are mutually antagonistic and are maintained in a relative state of balance. Take the transformation between yang-qi and yin-qi as an example. Yin-essence is the material basis for transforming into yang-qi,while the function of yang-qi is to produce yin-essence constantly. Thus, yang-qi and yin-essence are transformed and interact with one another, and are maintained in a relative balance. So it is said in Chapter 3 of Plain Questions, "Yin steady and yang consolidation results in harmonious life activities. "
In TCM, the yin-yang relationship also is used to expound on the concrete physio-
logical process. It is said in Chapter 5 of Plain Questions, "The lucid yang ascends to the upper orifices while the turbid yin descends to the lower orifices. The lucid yang loosens the interstitial space between the skin and flesh while the turbid yin enters the five zangviscera. The lucid yang enriches the four limbs, while the turbid yin returns to the six fu-viscera. " This means that all light and lucid materials pertain to yang, and all the heavy and turbid materials pertain to yin. So the human body's yang is the internal lightlucid qi, which can nourish and enrich the four limbs, and ascends to the upper orifices (such as the mouth and nose). The body's yin is the internal heavy-turbid materials,which can be stored in the five zang-viscera (referring to the visceral yin-essence) and can be discharged out of the body through the six fu-viscera and the lower orifices (such as the urinary tract or the anus).
It can be seen that TCM expounds upon the body's physiological activities from the systematic level. The normal life activities of the body result from the coordinated relationship of the unity of opposites between yin and yang, which causes yin and yang to be in relative dynamic equilibrium. "The correspondence between man and nature" refers to the fact that the body's visceral and meridians' functional activities adapt to the climatic changes of the four seasons. The use of this theory in TCM also is based on the correspondence of the wane-wax of the body's yin and yang to that of the natural world.
3. Explaining Pathology in the Body
It is held by TCM that the occurrence of disease is the result of the partial exuberance or decline due to an imbalance of yin and yang. The occurrence and development of disease is related to two aspects, the genuine-qi and the evil-qi. Yin and yang can be used to generalize and explain these two aspects and their relationship of interaction and interstruggle. The evil-qi can be divided into yang-evil and yin-evil, while the genuine-qi ineludes yin-essence and yang-qi. Therefore, imbalance of yin and yang in pathology usually shows the partial exuberance or decline in one aspect. Moreover, the abnormality of one aspect inevitably influences the other as well. For example, diseases caused by yang-
evil can lead to the partial exuberance of yang which further injures yin, making itself manifest in heat syndrome. Diseases caused by yin-evil can lead to the partial exuberance of yin which further injures yang, and thus makes itself manifest in cold syndrome. As another example, the insuffieieney of yang-qi fails to restrain yin, resulting in the deftciency-eold syndrome of excess yin with yang deficiency, while the insufficiency of yinfluid fails to restrain yang, leading to the deficiency-heat syndrome of hyperactivity of yang with yin deficiency.
So it is said in Chapter 5 of Plain Questions, "The predominant yin leads to disorder of yang, and the predominant yang leads to the disorder of yin. The predominance of yang brings about heat syndrome and the predominance of yin brings about cold syndrome. " Chapter 62 also says, "The yang deficiency leads to the exterior cold syndrome while the yin deficiency leads to interior heat syndrome. The yang exuberance brings about the exterior heat syndrome, while the yin exuberance brings about the interior cold syndrome. " Therefore, although the changes of diseases are complicated, changes in yin and yang can not go beyond the four large categories of yang exuberance, yin exorbitance, yang defieiency, and yin deficiency.
A degree of consumption of any aspect of yin or yang of the organism also will usually result in the insufficiency of its opposite, known as the "impairment of yang affecting yin" or the "impairment of yin affeeting yang. " This will result in defieieney of both yin and yang or the insufficiency of both qi and blood. This is the common process of pathological development in chronic diseases.
4. Application to Clinical Diagnosis and Syndrome Differentiation
The imbalance of yin and yang is the key of pathological changes. The clinical syndromes can be generalized as two large categories, yin syndrome and yang syndrome.
Thus, in clinic, the law of yin and yang changes is used to analyze and differentiate diseases and syndromes. It is proposed in Chapter 5 of Plain Questions, "Those who are good at diagnosis will differentiate yin and yang first when observing the color and feeling the pulses. " This explains that TCM's four diagnostic methods of observing, listening and smelling, questioning, and palpating should first be used to differentiate yin and yang.
Using the observation method as an example, the smooth and lustrous complexion
generally indicates yang, while the turbid and dim complexion suggest yin. All the syndromes accompanied with green, white, or black color pertain to yin-cold, and the syndromes with yellow or red color pertain to yang-heat.
As another example, the listening method also can shed light on the yin or yang determination. Husky breath and high voice indicate yang, while weak breath and low voice suggest yin. In palpitation, the pulse conditions such as floating, large, slippery, and rapid, etc. , are classified into yang-pulse, while the conditions such as deep, small, uneven, and slow, etc. , are classified into yin-pulse.
Syndrome differentiation refers to objectively analyzing and judging the patient's symptoms, physical signs and various disease condition data obtained through the four diagnostic methods in order to get correct conclusions about cause, location, and the nature of disease, as well as the relationship between the genuine-qi and the evil-qi, and to guide clinical treatment. TCM's diagnosis takes yin and yang as the general principle for syndrome differentiation, which is applied to differentiate the exterior and interior, the cold and heat, and the deficient and the excessive of disease. So all of the exterior, excessive,and heat syndromes pertain to yang syndrome, while all of the interior, deficient and cold syndromes pertain to yin syndrome. Thus, though the clinical diseases and syndromes may vary, they do not exceed the two principle ranges of yin and yang.
5. Guiding Clinical Treatment and Herb Application
Because the partial exuberance or decline of yin or yang is the fundamental cause for the occurrence and development of disease, the basic principle of TCM's therapeutics is to regulate yin and yang. In so doing, TCM aims to create conditions in which the imbalance of yin and yang will transform to the direction of coordination, and recover the relative balance that once existed. Thus, Chapter 74 in Plain Questions states, "To observe carefully where the disorder of yin and yang affect, and to regulate it, in order to achieve the goal of re-establishing the balance. "
Owing to the many different diseases, syndromes, and their natures, the therapeutic methods also are manifold. According to the objective at hand, various treatment methods are proposed in TCM's clinical activities, such as "treating the cold syndrome with hot-natured herbs," "treating the heat syndrome with cold-natured herbs," "treating the deficient syndrome by reinforcement," "treating the excessive syndrome by dispersion"(Chapter 74 of Plain Questions), and "treating yang disease from yin aspect and treating yin disease from yang aspect. " (Chapter 5 in the Plain Questions).
For example, for the syndrome of exuberant yang-heat consuming the yin-fluid (i. e. , predominant yang leads to the disorder of yin), treatment should involve cold-and cool-natured herbs to reduce the exuberant yang-heat, which is:the method of "treating the heat syndrome with cold-natured herbs. " If the syndrome is the exuberant yin-cold impairing yang-qi (i. e. , predominant yin leads to the disorder of yang), it should be treated with warm- and hot-natured herbs to reduce the exuberant yin-cold, which is the method of "treating the cold syndrome with hot-natured herbs. " In the insufficiency of yin-fluid failing to restrain yang leads to the syndrome of hyperactivity of yang due to yin deficiency, it must be treated with the method of nourishing yin for astringing yang; if insufficiency of yang cannot restrain yin, and the syndrome of yin occurs, it must be treated with the method of reinforcing yang to eliminate yin. These are the methods of "treating yang disease from yin aspect and treating yin disease from yang aspect. " Such methods were explained by Wang Bing as "strengthening the governor of water to restrain hyperactivity of yang, and boosting the source of fire to eliminate the abundance of yin. " This achieves the goal of recovering a new relative balance from the imbalance betweew yin and yang.
Similarly, yin and yang also have an important significance in classifying the herbs' nature, flavor, and function, and they can be taken as the basis in guiding clinical herb application. The general characteristics of herbs such as the four natures, five flavors,and ascending, descending, floating, sinking, etc. , all have the different properties of yin and yang. Taking the four natures as an example, the cold and cool pertain to yin and the warm and hot pertain to yang. As for the five flavors, herbs with sour, bitter, and salty flavors pertain to yin, while those with pungent, sweet, or weak flavors pertain to yang. Herbs with the features of heaviness, sinking, astringing, and descending pertain to yin, while those with the features of lightness, floating, ascending, or dispersing pertain to yang. Therefore, one must pay attention to the relationship between the syndrome's yin and yang, and the herb's yin and yang in the application of herbs in clinical practice. Correctly applying the herb's properties of yin and yang to improve or adjust
the pathological imbalanced relationship between the body's yin and yang is important in achieving the goal of curing disease.
