Chinese Medicine in Miniature
YIN YANG, THE FIVE ELEMENTS and QI
The Yin Yang principles and the Five Elements Theory are the ancient Chinese philosophical concepts.
You probably have ever heard about the book "Yi Jing", also named "The book of the Changing", the thousands years old of Chinese philosophical work is used to explain the 
phenomena of the universe.
Through the prolonged observation, experiments and experiences, man realized that Yin Yang are the two fundamental principles or forces in the universe which ever opposing and supplementing each other. For example, in the theory of Yin Yang, the heaven is considered as yang, while the earth yin and without heaven there would be no earth, and vice versa.
As day follows by night and spring by summer, everything in the universe is in a state of constant transforming from Yin into Yang and vice versa. This kind of motive force which behinds everything is known the Energy Qi, or cosmic Qi which exists in living beings as well as in "the dead" material.
The Five Elements i.e. Mu (wood), Huo (fire), Tu (earth), Jin (metal), Shui (water) are the five basic substances that constitute the material world.
Besides Yin Yang principles, this theory is also applied.