Yin & Yang
The teachings of yin and yang is the central underlying principle in TCM.
Traditional Chinese medicine sees good health to be the result of the harmonious balance of yin and yang. This balance is never static but is a constantly changing dynamic system.
Yin represents the substances found in nature and in the human body, e.g. blood, bodily fluids, muscles, tendons and tissue, and also the brain is a yin aspect. Yin also refers to cold and chronic illnesses. Yang, on the other hand, is responsible for the dynamics, the energy and activity of the muscles and organs. Qi is characterized as yang. Yang is heat. Yang stands for acute illness.
An imbalance between yin and yang manifests as certain symptoms or illnesses to which traditional Chinese medicine refers to as patterns of disharmony.