The theory of yin and yang

Ying and yang generally refer to two opposite aspects of interrelated things or phenomena in the natural world. The early connotations of ?yin and yang were quite simple, the side facing the sun being yang and the reverse side being yin. in the course of their everyday life and work, the ancient Chinese people came to understand that all aspects of the natural world could be seen as having a dual aspect, for example, day and night, brightness and dimness, movement and stillness, upward and downward directions, heat and cold, etc. thus the terms of yin and yang are used to express these dual and opposite qualities. The best example for the two primary opposite aspects of a contradiction is the relation between water and fire as described in su wen that “water and fire are the symbols of yin and yang.”
Based on the nature of water and fire, everything in the natural world can be classified into either yin and yang. Generally speaking, those with the basic nature of fire(such as heat, motion, ?brightness, upward and outward directions, excitement and potency)pertain to yang; while those with the basic nature of water(such as coldness, stillness, dimness, downward and inward directions, inhibition and weakness) pertain to yin. The book named yi zhuan says that “yin and yang are what is called dao” (dao means the basic law in the universe). in other words, everything in the universe contains both aspects of yin and yang. So yin and yang not only represent two opposite objects but are also used to analyze two opposite aspects within a single entity. According to such an understanding? of things, phenomena that are dynamic, bright, hot and functional pertain to the category of yang; while those that are static, dark, cold and substantial pertain to that of yin. The nature of yin and yang of a phenomenon is not absolute but relative. On the other hand, under certain conditions yin may change into yang and vice versa; and on the other, any phenomenon may be infinitely divided into its yin and yang aspects. The following figure is the symbol of yin and yang.
The theory of yin and yang holds that the development and changes of everything in the universe result from the unity and opposition between yin and yang. Su wen says: “yin and yang from the law of the heaven and earth (the natural world), the fundamental principles of all things, the parents (originators) of changes, the origin of birth and death…”
The unity and opposition between yin and yang
The opposition between yin and yang means that all things or phenomena in the natural world have two opposite aspects known as yin and yang, such as the heaven and earth, motion and quiescence ascending and descending, exiting and entering, day and night, heat and cold, etc. the former is yang and the latter yin every pair mentioned above. The unity is the result of mutual opposition and restriction between yin and yang. Without opposition, there would be no unity; without mutual opposition, there would be no mutual complement. It is just through this kind of opposition and restriction that the dynamic equilibrium can be established. For instance, in the natural world, the motions of celestial bodies, the variations of the four seasons, the alternations of days and nights as well as sprouting in spring, growing in summer, reaping in autumn and storing in winter, are all the concrete manifestations of the unity and opposition between yin and yang.
???? Traditional Chinese medicine holds that the normal physiological functions of the human body result from the opposite and unified relationship between yin and yang. Both of them are in? state of dynamic balance. Even under the normal physiological conditions of the human body, the balance between yin and yang is not absolute, but relative. If, for any reason, the relative balance is destroyed, there tends to develop xu(asthenia or deficiency) or shi(asthenia or excess) of yin or yang, as is stated in Su Wen that “predomination of yin results in yang disease while predomination of yang leads to yin disease.” It is precisely due to the unity and opposition between yin and yang that all things develop and change constantly.
Interdependence between yin and yang
Yin and yang oppose to and, at the same time, depend on each other. Neither can exist in isolation. In other words, without yin there would be no yang, and vice versa. So “if only yang exists, there will be no birth; if only yin exists, there will be no growth.” the life of every organism depends upon the correct balance of its various components. Such an interdependence between yin and yang is also reflected in the relationship between substance and function. the substance corresponds to yin and yang the function to yang. Thereby, there is no substance without function and no function without ??substance. That is why it is said in nei jing that: “yin remains inside to act as a guard for yang, while yang stays outside to serve as an actor of yin.” “yin” refers to the material basis and “yang” refers to functional activity. the substance and function are interdependent relationships between substances, between functions as well as between substances and functions become abnormal, life activities break down, bringing on dissociation of yin and yang, depletion of essence, and even an end of life.
Waning and waxing between yin and yang
Yin and yang coexist in a dynamic equilibrium in which one waxes (increases or grows) while the other wanes (decreases or decline). In other words, waning of yin will lead to waxing of yang and vice versa. Such a relationship between yin and yang is also described as inter-consuming-supporting relationship. The two aspects of yin and yang within any phenomenon are not fixed, but in a state of constant mutual consumption and support. For instance, various functional activities of the body will certainly consume nutrient substance. This process is what “consumption of yin leading to gaining of yang (or waning of yin leading to waxing of yang )”means. On the other hand, the production of various nutrient substances will inevitably consume energy. This process is what “consumption yang leading to gaining of yin (or waning of yang leading to waxing of yin) ”means. Take the seasonal and climatic variation for example. It gets warmer from winter to spring, and hotter from spring to summer. This is the process of “yang waxing leading to yin waning.” conversely, it gets cooler from summer to autumn, and colder from autumn to winter. This is the process known as “yin waxing leading to yang waning.” under normal conditions, the waning and waxing relationship or inter-consuming-supporting relationship between yin and yang is in a state of relative balance. If this relationship goes beyond normal limits, the relative balance of yin and yang will not be maintained, consequently resulting in either excess or deficiency of yin or yang and the occurrence of disease.
Inter-transformation between yin and yang
In given condition, either yin or yang may transform into its opposite side. That is to say, yin may transform into yang and yang into yin. if we regard the waning and waxing relationship between yin and yang as a process of quantitative change, then the Inter-transformation between yin and yang is a qualitative change. So it is said in su wen that “extreme yin turns into yang, while extreme yang turns into yin” and “extreme cold brings on heat, while extreme heat brings on cold.” that is why it is said that “things will turn into their opposites when they reach the extreme.” Pathologically, yin syndromes can transform into yang ones, and vice versa .it must be pointed out that the decisive factor for the mutual transformation is the necessary conditions, including internal conditions, without which such Inter-transformation can never occur.
The infinite divisibility of yin and yang
As mentioned above, yin and yang are in a state of constant change. That is why it is said in ling shu that “yin and yang have their names but no forms. For that reason it can be extended from one to ten, from ten to hundred, from a hundred to a thousand, from a thousand to ten thousand.”
According to the theory of yin and yang, in the natural world each component not only opposes to but also contains its opposite. So it is said in su wen that: “there is yin within yin and yang within yang. The period from dawn till noon is yang within yang; from noon till dusk is yin within yang; from dusk till midnight is yin within yin; from midnight till dawn is yang within yin.” In this way yin is divided into three levels known as taiyin, jueyin and shaoyin; while yang is divided into three degrees known as taiyang, shaoyang and yangming.
The three divisions of yin and the three divisions of yang are a further amplification of yin and yang. Such an amplification also reflects the waning and waxing relationship between yin and yang and is practical in clinical diagnosis and treatment. The exogenous febrile disease, for example, is differentiated and analyzed into taiyang, yangmign, shaoyang, taiyin, shaoyin and jueyin categories.

The theory of the five elements
The five elements refer to wood, fire, earth, metal and water in the natural world. In their daily life and work, the ancient Chinese people came to understand that these five categories of substances are the most essential ones indispensable to their existence. That is why the five elements were originally called “five materials.” It is said in zuo zhuan (Zuo’s interpretation of the Spring and Autumn Annals): “Nature produces five kinds of materials and people depend on these materials to live. None of them can be dispensed with.” Shang shu, another classical work, states: “water and fire are used for cooking; metal and wood are used for working; and earth gives birth to all things for people to use.”
The theory of the five elements holds that all phenomena in the universe correspond in nature either to wood, fire, earth, metal or water, and that these elements are in a state of constant motion and change. According to the mutual promotion and mutual restriction relationships among the five elements, nothing in nature is solitary and static. Though differing in characteristics, the five elements rely on each other and are inseparable. In the ancient times, these five elements and their mutual relationships were taken t explain the phenomena in the natural world. The primitive concept of the five elements was later evolved into a complete and complex theory which, together with the theory of yin and yang, serves as a theoretical tool for understanding and analyzing all phenomena.
In traditional Chinese medicine, the theory of the five elements is used to generalize and explain the nature of the zang-organs and fu-organs, the interrelations among these organs as well as the relationship between human being and the natural world, thus serving to guide clinical diagnosis and treatment.
According to this theory, everything in nature is attributed to one of the five elements. For instance, wood is characterized by growing freely and peripherally. So anything with the functions of growing, ascending and developing freely is attributed to the category of wood. Fire is characterized by flaming upward. Thereby anything with the functions of warming and rising is attributed to the category of fire. Earth is characterized by cultivation and reaping. So anything with the function of generating, transforming, supporting and receiving is attributed to the category of earth. Metal is characterized by change. Thereby anything with the functions of purifying, descending and astringing is attributed to the category of metal. Water is characterized by moistening and downward flowing. Therefore anything with the functions of cooling, moistening and moving downward is attributed to the category of water.
The early doctors applied the theory of the five elements to their extensive study of the physiology and pathology of the viscera and tissues in the human body as well as all the phenomena in the natural world that were related to human life. With analogy, they classified all these into the five elements according to their nature, function and form. They used this theory to explain complicated physiological relationships between the zang-organs and fu-organs as well as human body and the external environment.
The movement of the five elements is mainly characterized by inter-generation (or inter-promoting), inter-restriction (or inter-restraint), over- restriction (or over - restraint or subjugation),counter- restriction(or counteracting or restriction- restraint) and mutual interaction between mother-organ and child-organ.
Inter-generation means that one kind of object generates, strengthens or brings forth another one, i.e., wood generates fire, fire generates earth, earth generates metal, metal generates water, and water, in turn, generates wood. Each of the five elements is marked by such relationships as “being generated” and “generating.” This relationship of the five elements is termed as the “mother-child” relationship. Each element is the “child” of the element that generates it and the “mother” of the one it generates. Take wood for example. Since wood generates fire, it is the “mother” of life; because wood is generated by water, it is the “child” of water.
Restriction implies bringing under control or restraint. The restricting activity among the five elements follows a circular order: wood restricts (or acts on) earth, earth restricts (or acts on) water, water restricts (or acts on) fire, fire restricts (or acts on) metal, and metal, in turn, restricts (or acts on) wood. In this circular order, each of the five elements is marked by “being restricted” and “restricting.” For example, the element restricting wood is metal, and the element that is restricted by wood is earth.
Generation and restriction are two inseparable and indispensable aspects of the five elements. They oppose each other and also complement each other. Without generation, there would be no grow and development; without inter-restriction, there would be no balance and coordination during the development and change, thus resulting in excessive growth and bringing about harm. For example, wood generates fire and restrains earth; while earth generates metal and restrains water. Therefore the relative balance maintained between generation and restriction ensures normal growth and development. The ecological equilibrium in nature and physiological balance in the human body are the result of such relationships of generation and restriction among the five elements. These relationships are illustrated in the upper figure.
Over-restriction is similar to launching an attack when a counterpart is weak. It is an excessive restriction among the five elements. For instance, wood normally restricts earth. However, if wood is in excess, it may over restrict earth and brings on insufficiency of earth, also known as wood subjugating earth. The order of over-restriction is the same as that of restriction. Over –restriction is not a normal inter-restriction but a harmful condition occurring under abnormal circumstance.
Counter-restriction literarily means that the strong one bullies the weak one. Among the five elements it implies that one element preys another. It is a morbid condition in the which one element fails to restrict the other in regular order, but is restricted by the other in the reverse order. So the order of counter-restriction is just opposite to that of inter-restriction. For example, under normal conditions, metal restricts wood. But when wood is in excess or metal is in deficiency, wood will counter-restrict metal instead of being restricted by metal, which is known as “wood counter-restrict metal.” The order of over-restriction and counter restriction are illustrated in the following figure.
Over-restriction and counter-restrict are the abnormal inter- restriction in the five elements. They are different, but interrelated. The difference is that the order of the former is the same as that of restriction, while the order of the latter is just opposite to that of restriction. The interrelation is that both over- restriction and counter- restriction may occur simultaneously. Take wood for example. When it is excess, it may over- restriction earth and counter- restriction metal. Take metal for another example. When it is deficient, it may be counter- restriction by wood and over- restriction by fire.