At first , the theory of yin and yang was found in the classic book ” Zhou Yi ” (Canon of Changes ) . It was a spontaneous and naive dialectic philosophy in ancient China . Through development , the theory of yin and yang gradually became the general program elucidating the structure of the entire cosmos.

In Sinomedicine ( Traditional Chinese Medicine ) , the theory of yin and yang is used to explain physiological functions and pathological changes of the human body , and direct clinical diagnosis and treatment . Therefore , the theory of yin and yang is an important component in Sinomedicine.

1. Basic Concepts of Yin and Yang
Through observation of natural phenomena , the ancients recognized that every thing had two mutually opposed aspects , opposing each other and connecting each other . The ancients used yin and yang to generalize these two aspects , taking the interaction , movement , production and change of yin and yang as the program explaining changes of all things.

Yin and yang are the basic law of nature , the program of all things , the basis of changes and the origin of the processes in which things go through the beginning to the ending . Therefore , all things consist of yin and yang which are two opposed aspects , and the generation , development and change of all things are the results of mutual movement of the opposed yin and yang aspects .

Generally speaking , movableness , hotness , upperness , outside , brightness , hyperfunction , excitation , sturdiness ... are yang ; while quietness , coldness , lowerness , inside , dimness , decline , inhibition , weakness ... are yin .

Yin and yang properties of things are relative . On one side , yin can transform into yang and yang can transform into yin under certain conditions . On the other side , yin and yang can be subdivided into yin and yang . That is to say , there are yin and yang within yin , and there are yin and yang within yang . All things can be classified into yin-category and yang-category , any thing can be divided into yin-aspect and yang-aspect as well , and yin-aspect or yang-aspect can still be subdivided infinitely into yin and yang .

The law of movement of yin and yang shows in the following four aspects :

(1).Interdependence between yin and yang

Both yin and yang presuppose the existence of its opposed aspect . If any aspect seperates from the other opposed aspect , it can not exist alone .

(2).Growth and decline of yin and yang

Both yin and yang are not in the state of standstill and changelessness , while they are in movement and change of mutual growth and decline , i. e. ” decline of yang and growth of yin ” or ” decline of yin and growth of yang ” .

(3).Coordination of yin and yang

In normal state,growth and decline of yin and yang are coordinative , forming relation of synchronously mutual replenishment . If growth and decline of yin and yang are not coordinative , diseases will occur .

(4).Transformation between yin and yang

Under certain conditions , yin-aspect and yang-aspect of one thing can transform into its opposed aspect , i.e. yin can transform into yang , and yang can transform into yin as well .
2.Uses of the Concepts of Yin and Yang
In Sinomedicine , the concepts of yin and yang are used in anatomy , physiology , pathology , diagnostics , therapeutics and others .

[1].In Anatomy and Physiology

Yin and yang can be used to generalize the structures and functions of the human body . For the whole body of human being , the upper part is yang , while the lower part is yin ; the surface of body is yang , while the inside of body is yin ; the dorsum is yang , while the abdomen is yin ; the lateral part is yang , while the medial part is yin . For classification of zang-organs and fu-organs , the five zang-organs—the liver , heart , spleen , lung and kidney are yin , while the six fu-organs—the gallbladder , stomach , large intestine , small intestine , urinary bladder and triple warmer are yang . Among the five zang-organs , for those belong to the dorsum , the heart is a part of yang within yang , and the lung is a part of yin within yang ; for those belong to the abdomen , the liver is a part of yang within yin , the kidney is a part of yin within yin , and the spleen is a part of extreme yin within yin .

The normal life activities of the human body are the results that yin and yang keep coordinative relation of unity of opposites , and they are the processes of coordination and unity of assimilation in which ” yin gives shape to things ” and dissimilation in which ” yang forms vital energy”.

[2].In Pathology

Diseases are caused by abnormality of coordination of yin and yang in the body . Although pathological changes are very complicated , they can be generalized by using the concepts of yin and yang . Generally speaking , the diseases which show chronic , cold , asthenic and hypofunctional pathological changes belong to yin syndromes ; the diseases which show acut , hot , sthenic and hyperfunctional pathological changes belong to yang syndromes .

[3].In Diagnostics

The basic cause of genesis and development of a disease is abnormality of the coordination of yin and yang . Therefore , to diagnose correctly , yin and yang should be distinguished first , so that the nature of a disease can be grasped . For inspection , bright and lustrous color in the skin belongs to yang , while dark and gloomy color belongs to yin ; for auscultation and olfaction , a loud and clear voice belongs to yang , while a low voice belongs to yin ; for palpation and pulse-feeling , such pulse conditions as floating pulse , rapid pulse and large pulse belong to yang , while sunken pulse , slow pulse and small pulse belong to yin .

[4].In Therapeutics

Diseases result from abnormality of coordination of yin and yang . Therefore , the general principle of treating diseases is returning coordination of yin and yang to normal , i. e. invigorating its insufficiency or attenuating its excess according to excess or insufficiency of yin and yang to correct the phenomenon of excess tendency or insufficiency tendency of yin and yang,and to return yin and yang to normal coordinating relation .