The principal theories of TCM include Yin and Yang theory, Qi, Blood and Body Fluid theory and Channels and Collaterals theory.

1. 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. 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.

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

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 transmitting 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 channels 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.

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 (hypofunction) symptoms and signs.

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 esthetic 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 drug cold in nature. Preponderance of yin leads to hypofunction of the organism or endogenous cold which 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. This 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 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, flavour 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 flavours belong to yin, while the herbs with pungent, sweet and bland flavours, 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.

2. The Theory of Qi, Blood and Body Fluid

TCM believes that the qi, blood and body fluid are the basic components of the body and maintain the life activities of the human body. It is from qi, blood and body fluid that comes the energy needed by viscera and bowels, channels and collaterals, tissues and other organs for performing their physiological functions. On the other hand, their formation and metabolism depend on the normal physiological functions of viscera and bowels, channels and collaterals, tissues and other organs. Therefore, it is true to say that qi, blood and body fluid are not only the material basis of the functional body fluid are not only the material basis of the functional activities of viscera and bowels, channels and collaterals, tissues and other organs, but also the physiological products of their functional activities. They complement each other and have mutual causality in many aspects such as physiology and pathology.

The theory of qi, blood and body fluid is a theory used to study the development, transportation and distribution, physiological functions, pathological changes and mutual relations of qi, blood and body fluid of the human body.

What is meant by qi? The concept of qi is based on the ancient Chinese initial understanding of natural phenomena. That is, qi is the most basic substance of which the world is comprised. Everything in the universe results from the movements and changes of qi. This concept was introduced into TCM and became one of its characteristics. After a comprehensive survey of the statements on qi in TCM documents, we have come to the conclusion that the meaning of qi in TCM has two aspects. One refers to the vital substances comprising the human body and maintaining its life activities, such as the qi of water and food (food essence), the qi of breathing (breathing nutrients) and so on. The other refers to the physiological functions of viscera and bowels, channels and collaterals, such as the qi of the heart, the lung, the spleen and the stomach and so on. The qi here referred to, is specifically the physiological functions of these viscera and bowels.

Different kinds of qi have different functions. Generally speaking, they can be summarized as follows:

1) Promoting Action

Qi is a sort of essence full of vitality. It can help activate the growth and development of the human body, promote the physiological functions of each viscus, bowel, channel, collateral, tissue and organ and speed up the formation and circulation of blood and the metabolism of body fluid as well. For example, if the above functions are weakened as a result of the deficiency of qi ( vital energy), the following will occur: late and slow growth and development of the human body or senilism; weakened functions of viscera and bowels, channels and collaterals, tissues and other organs; insufficient blood formation or stagnation in blood vessels; and disturbance in the metabolism of body fluid.

2) Defending Action

The defending action of qi is shown in two aspects. One is to guard the surface of the skin against the exopathogen. The other is to combat the invading exopathogen so as to ward it off. When the defending function of qi is normal, the exopathogen has difficulty in invading the body, even though it may obtain entry, it is not certain to cause any disease. If it does cause a disease, this disease is easy to cure. When the defending function of qi becomes weaker, when the ability of the human body to fight the exopathogen is lowered, the body is easily invaded and diseases are caused. And what is more, these diseases are hard to cure.

3) Consolidating and governing Action

By consolidating and governing action, we mean that qi has the ability to command, control and consolidate the liquid substances and organs in the abdominal cavity. This is done by:

(1) Keeping the blood flowing within, not extravasating out of, the vessels;

(2) Controlling and adjusting the secretion and excretion of sweat, urine and saliva, and preventing the body fluid from escaping;

(3) Consolidating and storing sperm and preventing emission and premature ejaculation;

(4) Consolidating the organs so as to prevent them from descending.

A decrease in the above functions of qi may cause various kinds of hemorrhage, spontaneous, polyuria, salivation, spermatorrhea, premature ejaculation, prolapse of the stomach, kidney and uterus.

The consolidation and governing action and the promoting action of qi oppose each other and yet also complement each other. On the one hand, qi has the function of promoting the circulation of blood, and the transportation and distribution of body fluid. On the other hand, it also has the function of controlling and adjusting the movement, secretion and excretion of liquid substances in the body. The coordination and balance of these two functions are essential for maintaining normal blood circulation and water metabolism within the body.

3. The Theory of the Channels and Collaterals

The theory of channels and collaterals concerns the study of the physiology and pathology of the channels and collaterals, and their mutual relations. It is as essential a part of the basic theory of TCM as the theory of yin and yang, qi, blood and body fluid. It forms the basis of all clinical departments of TCM, especially of acupuncture, moxibustion and massage.

What is meant by the channel and collateral? The channel, or "jing" in Chinese, means route, and is the main trunk running lengthways in the system of the channels and collaterals; while the collateral, or "luo" in Chinese, means net, and is the branch of a channel in the system.

TCM holds that the channels and collaterals are distributed over the whole body. They are linked with each other and connect the superficial, interior, upper and bower portions of human body, making the body an organic whole. The system of the channels and collaterals consists of channels, collaterals and their subsidiary parts.

The channels may be divided into regular channels and extra channels. There are twelve regular channels, including three yin channels of the hand and toot, and three yang channels of the hand and foot. They are referred to altogether as the Twelve Channels. The Eight Extra Channels consist of what is called the Du Channels, the Ren Channel, the Chong Channel, the Dai Channel, the Yinqiao Channel, the Yangqiao Channel, the Yinwei Channels and the Yangwei Channel. They are commonly referred to as the Eight Extra Channels.

The collaterals can be classified as the reticular branch conduits, superficial collaterals, and small collaterals. All the Twelve Channels, and the Du and the Ren Channels have one reticular branch conduit each. These reticular branch conduits and the great reticular conduit of the spleen add up to fifteen. The superficial collaterals are the ones that run in the surface layer of the human body, and often make their appearance on the surface. The small collaterals are the finest.

The distributing law of the Twelve Channels is: In the region of the head and face, the Channels of Hand-Taiyang and Foot-Taiyang run through both sides of the head, while the Channels of Hand-Yangming and Foot-Yangming run through the face and forehead. The Channels of Hand-Taiyang and Foot-Taiyang run through the cheek, the vertex and the back of the neck. In the region of the trunk, the three yang channels of the hand run through the shoulder. Of the three yang channels of the foot, the Yangming runs in front of the trunk (the ventral aspect), the Taiyang along the back (the dorsal aspect), and the Shaoyang along the sides. All three yin channels of the hand exit from the axilla without exception. All three yin channels of the foot run through the surface of the abdomen. The channels running through the surface of the abdomen are termed Foot-Shaoyin, Foot-Yangming, Foot-Taiyin, Foot-Jueyin in order of their distribution from inside to outside.

The channels and collaterals have a direct bearing on the occurrence and progress of diseases. If a channel is in functional disorder, it is apt to be attacked by exogenous factors; then the exogenous factors will further intrude into the internal organs along the channels.

The channels and collaterals are not only the route along which exogenous factors intrude into the internal organs from the body surface, but also the way through which the pathological changes between the viscera, and between the internal organs and the tissues of the body surface affect one another. For instance, just as the Liver Channel of Foot-Jueyin runs by the stomach and pours into the lung, so liver disease may affect the stomach or lung; owing to the fact that the Kidney Channel of Foot-Shaoyin enters the lung and connects with the heart, the retention of fluid, which is due to kidney-asthenia, may attack the lung or heart; and because the Heart Channel of Hand-Shaoyin runs along the posterior border of the medial aspect of the upper arm, angina pectoris often radiates to the region.

As the channels differ in their running courses and pertaining organs, during the diagnosis an inference about the channel or organ where pathological changes take place can be drawn from the analysis of where symptoms and signs are located. For example, pains in the hypochondrium probably indicate that the trouble lies in the liver or gall bladder because the hypochondrium is the region where travel Liver Channel of Foot-Jueyin and the Gallbladder Channel of Foot-Shaoyang; pains in the supraclavicular fossa are mostly caused by lung disease because the supraclavicular fossa is the place where the Lung Channel of Hand-Taiyin passes. Another example, headache may be diagnosed in the light of the distributing law of the channels on the head because the pain in the forehead is most probably cause by Yangming Channel disturbance; migraine by Shaoyang Channel disturbance; pains of the back of the head and neck by Taiyang Channel disturbance and pain of the top of the head by Jueyin Channel disturbance. In recent years, people have also found that tenderness may occur at Point Zhongfu (L 1) in case of lung disease, at Point Lanwei (Extra 37) in case of acute appendicitis, etc. All these discoveries are helpful in diagnosis.

The theory of the channels and collaterals has long been widely applied to direct clinical treatment of all the departments of TCM, in particular, acupuncture, moxibustion, massage and herbal prescriptions. For instance, the method of selecting points along the channels is a good example. To be more specific, Point Zusanli (S 36) of the Stomach Channel of Foot-Yangming should be selected for the treatment of stomachache; Point Qimen (Liv 14) of the Liver Channel Foot-Jueyin should be punctured for curing liver disease. The selection of region of massage is also based on this theory.

It is also through the channels and collaterals that the herbs exert an influence on the pathological region and take effect as expected. Through protracted and repeated practice, TCM doctors have discovered that a certain herb possesses a selective effect for a certain disease of some channel and its pertaining organ, thus creatively formulating a theory of classifying herbs according to their respective therapeutic effect on the disease of a specific channel and its pertaining organ. For example, through the work done by Chinese ephedra (Herba Ephedrae) on the channels of the lung and urinary bladder, sweat is induced, asthma relieved, and diuresis promote. Another example, thorowax root (Radix Bupleuri) acts on the channels of the liver and gall bladder, so as to disperse the depressed energy of the liver and gall bladder, and regulate the vital energy by alleviation of mental depression. Zhang Jiegu and Li Gao, two of the four great physicians in the Jin and Yuan dynasties, formulated a theory of medicinal guides according to the theory of the channel and collaterals. For instance, in treating headache, notopterygium root (Rhizoma seu Radix Noto pterygii) should be prescribed if it is due to Taiyang disturbance, or dahurian angelica root (Radix Angeliecae Dahuricae) should be prescribed if due to disturbance of the Yangming, or thorowax root (Radix Bupleuri) prescribed if due to disturbance of the Shaoyang. The above mentioned "medicinal guides" do not only work their way through the relative channel and its pertaining organ, but also direct other medicines to the right channel and organ in order to bring their therapeutic action into play.

In addition, the clinical applications of acupuncture anaesthesia, auricular needle are done under the guidance of the theory of the channels and collaterals, and will inevitably further prove and develop this theory.

---------- Source Basic Theory of Traditional Chinese Medicine