Yin and Yang
Yin and yang are ancient Daoist philosophical concepts that describe the universe and everything in it as being divisible into two principal categories that balance and complement each other. In nature, examples of this include night and day, moon and sun, winter and summer, valley and mountain, ocean and desert. Within our bodies, yin and yang are reflected in things like the balance of cold and heat, dryness and moisture, activity and rest, and in the interdependent relationship of our physical body with our immaterial mind and spirit. At its core, the theory of yin and yang expresses the true nature of all phenomena as it continually shifts and cycles in and out of phase. Four universal laws govern the relationship between yin and yang and they apply to everything in existence, including us.
Yin and Yang are Opposites
Everything in the universe can be categorized as either yin or yang. These two categories are relative, however, not absolute. For example, a 55-degree day feels cool (more yin) if it occurs at the height of summer, but warm (more yang) if it occurs in the middle of the winter. In other words, the yin or yang nature of anything can only be defined in relation to something else. Paradoxically, this means that, depending on what it is being compared to, nothing is absolutely either yin or yang. It also means that everything is simultaneously both yin and yang.
Yin and Yang are Interdependent
Yin and yang are interdependent and cannot exist without each other. For example, there cannot be day without night, expansion without contraction, or activity without rest. In reality, yin and yang are two different aspects of the same singular unity that is constantly shifting from one form to another. Sometimes this change happens very gradually, as seen in seasonal shifts, and sometimes it happens quite abruptly, like a sudden cooling thunderstorm on a hot summer afternoon.
Yin and Yang Balance Each Other
Yin and yang are in a constant state of dynamic balance. Because yin and yang are interdependent, the level of one must go down if the level of the other goes up and vice-versa. There are four basic scenarios in this balance of opposites: excess yin, excess yang, deficient yin, or deficient yang. This can lead to an interesting situation where the excess of one can mimic the deficiency of the other and the deficiency of one can mimic the excess of the other. In either case, the relative imbalance is in a similar proportion. For example, there can be signs of heat with both excess yang and deficient yin, because in both cases there is more yang than yin. A classic example of this is hot flashes, which are referred to as deficient heat or false heat and are considered to be caused not by an excess of yang but by a deficiency of yin.
Yin Can Transform into Yang and Yang Into Yin
Because yin and yang are two aspects of the same thing, they can transform into one another. This ability to transform, however, does not happen randomly but logically, according to the rules of the universe. First, there has to exist an inherent capacity, a potential possibility for the change to take place. For example, an oak tree (yang) can emerge from an acorn (yin) but a pine tree cannot. Second, this transformation can only occur at specific stages of development, when the conditions are ripe for change. For example, the acorn will only grow into an oak if it is planted in the right soil and if there is the right amount of sun and water.
Good and Bad, Right and Wrong, Yin and Yang
Certain dualities do not apply to the philosophy of yin and yang, like good and bad or right or wrong. In Chinese medicine, things just have different natures and properties that make them helpful for certain conditions and types of people and harmful for others. This means that a thing that might benefit one type of condition or person may aggravate another. This non-duality is a very important and essential part of this philosophy and reflects its relativistic understanding of the universe - because everything is connected, anything and everything can only be defined in relation to something else.
