The Theory of Yin-Yang

The Opposition of Yin and Yang

The theory of Yin-Yang holds that every object in the universe consists of two opposite aspects which are in continual mutual restriction and interaction. The alternation of the four seasons is an example. The spring is warm and the summer hot. This is due to the rising of yang qi which restricts the autumn cool and the winter cold. Alternately, the coolness of autumn and cold of winter arise because of the ascendancy of yin that restricts the spring warmth and summer heat. According to Yin-Yang theory, the seasonal cycle is the outcome of the mutually restrictive and mutually consuming-increasing activities of yin and yang. Either side of the two opposites always restricts and acts on the other. This process of mutual restriction and interaction is the operation of yin and yang, without which change would not occur. Thus the two opposites of yin and yang do not exist as an entity in a still and unconcerned state. They constantly interact with each other, hence the alteration and development of an object.

Yin and Yang Interdependence

Yin and yang are at once in opposition and in interdependence. They rely on each other for existence, coexisting in a singe entity. Each of the two aspects is the condition for the other's existence and neither can exist in isolation. For example, daytime is yang, night in yin, without day there would be no night; upper is yang, lower is yin; left is yang, right is yin, etc., each pair exists in a state of mutual dependence, and without its opposite it could not exist. The interdependent relationship of yin and yang is described in the Suwen, "Yin is installed in the interior as the material foundation for yang, while yang remains on the exterior as the manifestation of the yin function." This is a traditional explanation of the interdependence of yin and yang.

The Mutual Consuming-Increasing Relationship of Yin and Yang

The yin and yang aspects within an object are not quiescent, but in a state of constant motion. They can be described as being in a state where the lessening of yin leads to an increase of yang, or vise versa. Taking the transformation of the seasons as an example, in terms of the Yin-Yang theory, the process of transition from winter cold through spring warmth into summer heat demonstrates the process of a lessening of yin leading into an increasing of yang. While the transition from the heat of summer to the cold of winter is the lessening of yang leading to an increasing of yin.

Regarding the human body's functional activities, which are considered yang, the consumption of nutrient substances, which are considered yin, results in the lessening of yin to the increase of yang. As the metabolism of nutrient substances (yin) exhausts the functional energy (yang) to a certain extent, this is understood as a lessening of yang to the increase of yin. Under normal conditions the mutual consuming and increasing of yin and yang maintain a relative balance. Under abnormal conditions there is an excess or insufficiency of either yin or yang which leads to the occurrence of disease.

Yin and Yang's Mutual Transforming Relationship

In certain circumstances and at a certain stage of development, each of the two aspects of yin and yang, within an object, will transform from yin into yang and from yang into yin. The mutual consuming-increasing of yin and yang is a process of quantitative change, and the mutual transformation of yin and yang is a process of qualitative change. The Suwen comments, "Extreme cold will bring about heat, and extreme heat will induce cold..."; furthermore, "Excessive yin may cause yang syndromes or tend to be transformed into yang and vice versa." These are the features and conditions of the mutual transformation of yin and yang.

The mutual transformation of yin and yang is often seen during the development of a disease. For example, if a patient has a constant high fever, which is suddenly lowered, accompanied by a pale complexion, cold limbs, extremely feeble pulse (the danger symptoms of yin cold syndromes), we may say that the disease has transformed from a yang syndrome into a yin syndrome. Under these circumstances, proper emergency treatment should warm the limbs to make the pulse normal. The yang qi will recover, and the danger will be removed. Thus yin syndromes can change into yang syndromes. Clinical practice provides other examples of the mutual transformation of yin and yang. It is common in clinical practice to have exterior syndromes transform into interior syndromes or vice versa and shi (excess) syndromes may change into xu (deficiency) syndromes or vice versa.

The above-mentioned relationships of mutual opposing, depending, consuming-increasing, and transforming of yin and yang are the basic content of Yin-Yang theory. Furthermore, these four relationships between yin and yang are not so isolated from each other but interconnect with and interact upon each other.