Yin / Yang:

Two halves that together complete wholeness. Yin and yang are also the starting point for change. When something is whole, by definition, it’s unchanging and complete. So, when you split something into two halves – yin/yang, it upsets the equilibrium of wholeness. Both halves are chasing after each other as they seek a new balance with each other. The word Yin comes out to mean “shady side” and Yang “sunny side”.  Yin Yang is the concept of duality forming a whole. We encounter examples of Yin and Yang every day. As examples: night (Yin) and day (Yang), female (Yin) and male (Yang). Over thousands of years, quite a bit has been sorted and grouped under various Yin Yang classification systems.

Yin Yang illustrated:

When people see things as beautiful, ugliness is created. When people see things as good, evil is created. Being and non-being produce each other. Difficult and easy complement each other. Long and short define each other. High and low oppose each other. Fore and aft follow each other.

The Nature of Yin Yang

1. Neither Yin nor Yang is absolute. Nothing is completely Yin or completely Yang. Each aspect contains the beginning point for the other aspect. For example, day becomes night and then night becomes day. Yin and Yang are interdependent upon each other so that the definition of one requires the definition for the other to be complete.
2. Yin Yang is not static. The nature of Yin and Yang flows and changes with time. A simple example is thinking about how the day gradually flows into the night. However, the length of day and night are changing. As the earth ages, its spin is slowing causing the length of day and night to get longer. Day and night are not static entities. Sometimes changes in the relationship between Yin and Yang can be dramatic where one aspect can just transform into the other. As an example: some species of fish have females that transform quickly into males when the population of males isn’t enough.
3. The summation of Yin and Yang form a whole. One effect of this is: as one aspect increases the other decreases to maintain the overall balance of the whole.
4. The balance of Yin Yang can be skewed due to outside influences. Four possible imbalances exist:
   1. Deficiency Yang
   2. Deficiency Yin
   3. Excess Yang
   4. Excess Yin

These imbalances can be paired: so, an excess of Yin can also simulate a Yang deficiency and vice versa. So, an excess of Yang results in a fever. An excess of Yin could mean the accumulation of fluids in the body. Chinese healing examines a person’s health by using the eight principles: Internal and External stimuli, Deficiency and Excesses, Cold and Heat and Yin and Yang.

• Yin Yang can be subdivided into additional Yin and Yang aspects. For example, a Yang aspect of Heat: can be further subdivided into a Yin warm or Yang burning. Yin-Yang

• The yin-yang philosophy says that the universe is composed of competing and complementary forces of dark and light, sun and moon, male and female. 
• The philosophy is at least 3,500 years old, discussed in the ninth-century BCE text known as I Ching or Book of Changes, and influences the philosophies of Taoism and Confucianism.
• The yin-yang symbol is related to the ancient method used to track the movements of the sun, moon, and stars around the year. 

Generally speaking, yin is characterized as an inward energy that is feminine, still, dark, and negative. On the other hand, yang is characterized as outward energy, masculine, hot, bright, and positive. 

A Subtle and Cosmic Duality

Yin and yang elements come in pairs—such as the moon and the sun, female and male, dark and bright, cold and hot, passive and active, and so on—but note that yin and yang are not static or mutually exclusive terms. While the world is composed of many different, sometimes opposing, forces, these can coexist and even complement each other. Sometimes, forces opposite in nature even rely on one another to exist. The nature of yin-yang lies in the interchange and interplay of the two components. The alternation of day and night is just such an example: there cannot be a shadow without light.  The balance of yin and yang is important. If yin is stronger, yang will be weaker, and vice versa. Yin and yang can interchange under certain conditions so that they are usually not yin and yang alone. In other words, yin elements can contain certain parts of yang, and yang can have some components of yin. This balance of yin and yang is perceived to exist in everything.