The theory of yin-yang originated in ancient China and it deals with the origin of the universe as well as the motion and variation of all things in the natural world. It holds that the natural world is made up of materials and that the material world conceives, develops and constantly varies under the interaction of yin and yang. The philosophers and doctors in ancient China explained all the phenomena and the nature of the universe and life with the theory of yin-yang. They regarded the opposition, the wane and was as well as the variation of yin-yang as “the law of the universe”.
1. The implication of yin-yang & the categorization of things according to the nature of yin-yang
People in ancient China held that the original state of the universe was “Qi” and that the motion and variation of “qi” produced two poles knows as “yin” and “yang”, such a process of transformation was called “to divide one into two”. Since all the things in the universe are produced through the motion and variation of qi, everything can be divided into the aspects of yin and yang, such as the heaven and the earth, the day and the night, the water and fire, upper and lower, cold and heat as well as man and woman, etc.
1.1 The implication of yin-yang
The original meaning of yin and yang is simple and specific, mainly referring to the sides facing and opposite to the sun. That is to say that the things facing the sun pertain to yang while the things opposite to the sun pertain to yin. In Chinese “yang” means “sunshine” while “yin” means “shadow”. Later on specific things related to yin and yang were abstracted to induce a series of properties in the light of yin and yang. In this way yin and yang, two special signifiers, gradually evolved into a theory of extensive application. Consequently the implication of yin and yang was extended.
The properties of things signified by yin and yang are quite abstract. In order to make the meaning of yin and yang explicit, people in ancient China used specific things, namely water and fire, as metaphors to analogize. Since water and fire are opposite to each other in nature and reflect the basic characteristics of yin and yang, they are used as the signifiers of yin and yang in Huangdi Neijing. Comparatively speaking, fire is warm, bright, active and up-flaming; while water is cold, dim, static and downward-moving. That is why it si stipulated in Huangdi Neijing that “water is yin and fire is yang”
1.2 The categorization of things according to yin and yang
Fire and water are the evidences used to categorize things because they are the signifiers of yin and yang, Generally speaking, the things and the phenomena that bear the properties of being warm, bright, active, rising the dispersing pertain to yang; while the things and the phenomena that bear the properties of being cold, dim, static, descending and astringing pertain to yin.
According to such criteria, all things and phenomena can be categorized into either yin or yang group. However, the yin and yang properties of things are relative, not absolute. In the categorization of things according to the nature of yin and yang, two point have to be taken into consideration.
(1) the yin or yang properties of things may vary with the change of time and application. Take spring and summer for example, it is comparatively hot in summer and cold in spring, so summer pertains to yang and spring to yin. Take spring and winter for another example. It is comparatively cold in winter and warm in spring, so winter pertains to yin while spring to yang.
(2) Any aspect of yin and yang in an object can be further and infinitely divided. In this case there exists yin within yang and yang within in. take daytime and night for example, daytime can be further divided into two phases: morning and afternoon. Since yang-qi ascends in the morning and descend in the afternoon, morning pertains to yang (yang within yang) and afternoon to yin (yin within yang). Similarly, night can be divided into anterior night and posterior night. Since yin-qi increases in the anterior night and decreases in the posterior night, anterior night pertains to yin (yin within yin) while posterior night to yang (yang within yin).
1.3 Interaction between yin and yang
The yin and yang aspects within an object or phenomenon are not simply arbitrary divisions. In fact they are in constant and complicated interaction. Such interactions between yin and yang give rise to the origination, development and change of things. The interaction between yin and yang are various in manifestations. The following is a brief description of the major ones.
1.3.1 Opposition of yin and yang
Since yin and yang are opposite to each other in nature, they constantly repel and restrain each other. If both yin and yang are quite powerful, such a mutual repelling and restraining activity will maintain general equilibrium of things. If one side is weak and the other side is strong, and the strong side will restrain the weak side, consequently damaging the general balance of things. The so-called “contrary treatment”, one of the basic therapeutic principles in TCM, is developed in the light of the opposition between yin and yang. For example, the treatment of cold disease with drugs hot in nature means to use heat (yang) to control cold (yin) while the treatment of febrile disease with drugs cold in nature means to use cold drugs (yin) to restrict heat (yang). Since the drugs used and these disease treated are different in nature, such a treatment is termed “contrary treatment”. “Contrary” means “opposite”.
1.3.2 Interdependence between yin and yang
Interdependence between yin and yang, literarily yin and yang rooting in each other, indicates that yin and yang depend on each other for existence in an object. In conception, yin and yang must exist in pair and no side can exist solitarily. In nature, yin and yang within an object can transform into each other under certain condition, implying that no one can exist without the existence of the other, that is why it is said in the theory of TCM that “solitary yang can’t exist” and “solitary yin can’t grow”. In the light of interdependence between yin and yang, TCM pays much attention to mutual transformation between qi and blood as well as yin and yang in the treatment of disease due to deficiency of qi and blood as well as of yin and yang. For example, the patients with blood deficiency cam be treated by supplementing qi to product blood, the patients with qi deficiency can be treated by supplementing blood to promote qi, the patients with yin deficiency can be treated by supplementing yang to generate yin (also called “drawing yin from yang”) and the patients with yang deficiency can be treated by supplementing yin to promote yang (also called “drawing yang from yin”)
1.3.3 Wane and wax between yin and yang
Wane and wax between yin and yang implies that, in the interaction between yin and yang, one side is developing while the other side is declining and vice versa. Such a state manifests in different ways, such as yin waning while yang waxing, yin waxing while yang waning, yang waning leading to yin waxing, and yang waxing leading to yin waning.
Under normal condition, wane and was between yin and yang are maintained to a certain range. Waning to a certain degree will turn toa certain rage. Waning to a certain degree will turn to waxing and waxing to a certain level will change into waning. In this way wane and wax will never be excessive. Alternation and repetition of wane and wax maintain a dynamic balance between yin and yang.
If wane and wax between yin and yang exceeds the normal level, relative predominance or relative decline of either yin or yang will arise, consequently damaging the dynamic balance between yin and yang and leading to imbalance of yin and yang.
1.3.4 Mutual transformation between yin and yang
If yin or yang wane or waxes to the extreme point, it will turn to the opposite. That means yin will change into yang and yang into yin. The key element involved in such a mutual transformation is the degree of wane and wax. The degree that leads to transformation is termed “extreme point” or “excess” in TCM. In Huangdi Neijing, it suggests that “extreme cold generates heat”, ”extreme heat generates cold”, “excessive yin turns into yang” and “excessive yang changes into yin”, all reflecting mutual transformation relationship between yin and yang.
The typical mutual transformation process of yin and yang is well signigied by the variations of yin and yang in the four seasons of a year. From spring to summer, yang waxes while yin wanes, however when such a transformation reached the peak-the summer solstice, yin begins to wax while yang starts to wanes. But when such a transformation reaches the peak- the winter solstice, yang begins to wax while yin starts to wane. Such a change exactly explains the idea that “excessive yin turns into yang” and “excessive yang changes into yin”. With the wane and wax of yin and yang, cold and heat in the climate also alternate. Such an alternation vividly demonstrate the theory that “extreme cold generates heat” and “extreme heat generates cold”.