"... yin and yang are ancient philosophical concepts that remain incredibly useful both inside and outside traditional Chinese medicine: they provide a way of thinking through contradiction, change, and continuity.
Yin (阴) and yang (阳) originally served as direction markers: yin indicated the shady side, facing away from the sun, and yang the sunny side, facing toward the sun. These original meanings expanded alongside the development of Chinese philosophical thought, becoming a core principle of duality that explained seasonal change, bodily function, and the birth and development of the universe. Yin came to signify things that were lower, darker, colder, wetter, heavier. Night is yin, as are fall and winter. Yang, on the other hand, signifies things that are higher, lighter, warmer, drier, livelier. Daytime, spring, and summer are all yang. While yin and yang can be separately identified, they can’t themselves be separated. There’s no day without night, no warm without cool, no summer without winter. Things are yin and yang relative to each other, existing in dynamic states of equilibrium that facilitate both transformation and stasis, and ensure continuity through contradiction ..." (read more)