"The Five Elemental Energies of Wood, Fire, Earth, Metal, and Water encompass all the myriad phenomena of nature. It is a paradigm that applies equally to humans."
By the transformation of yang and its union with yin, the Five Elemental Energies of Wood, Fire, Earth, Metal, and Water arise, each within its specific nature according to its share of yin and yang. These Five Elemental Energies constantly change their sphere of activity, nurturing and counteracting one another so that there is a constancy in the transformation from emptiness to abundance and abundance to emptiness, like a ring without beginning or end. The interaction of these primordial forces brings harmonious change and the cycles of nature run their course . . . The Five Elemental Energies combine and recombine in innumerable ways to produce manifest existence. All things contain all Five Elemental Energies in various proportions.
from The Yellow Emperor's Classic of Internal Medicine