The Way of Yin and Yang
一阴一阳之谓道，继之者善也，成之者性也。
The alternation of Yin and Yang is called the Dao. That which carries it forward is goodness; that which completes it is nature.
—— 《周易·系辞传上》Xici Zhuan (Great Treatise), Part I
What is Yin and Yang?
阴阳是中国古代哲学的核心概念，用以描述宇宙万物中相互对立又相互依存的两种基本力量。 阳代表积极、主动、刚健、光明；阴代表消极、被动、柔顺、黑暗。 阴阳并非绝对对立，而是相互转化、相互包含的统一体。
Yin and Yang are the core concepts of ancient Chinese philosophy, describing two fundamental forces that are both opposite and interdependent in all things of the universe. Yang represents the active, dynamic, strong, and bright; Yin represents the passive, receptive, soft, and dark. They are not absolutely opposed but form a unity of mutual transformation and inclusion.
易有太极，是生两仪，两仪生四象，四象生八卦。
The Changes has the Great Ultimate (Taiji), which generates the Two Forms. The Two Forms generate the Four Images. The Four Images generate the Eight Trigrams.
The Four Principles of Yin-Yang
Opposition and Unity
阴阳相反相成，矛盾对立统一。如天与地、日与月、昼与夜、男与女。
Yin and Yang are opposite yet complementary, contradictory yet unified. Like heaven and earth, sun and moon, day and night, male and female.
「天尊地卑，乾坤定矣」
Mutual Rooting
阴中有阳，阳中有阴。互为根本，不可分离。阴离阳则无以生，阳离阴则无以化。
Yin contains Yang, Yang contains Yin. They are mutually rooted and inseparable. Yin without Yang cannot generate; Yang without Yin cannot transform.
「孤阴不生，独阳不长」
Waxing and Waning
阴阳此消彼长，处于动态平衡之中。如四季更替、昼夜交替、月相盈亏。
Yin and Yang wax and wane in dynamic balance. Like the changing seasons, alternating day and night, waxing and waning moon.
「日中则昃，月盈则食」
Mutual Transformation
阴极生阳，阳极生阴。物极必反，循环往复。寒极生热，热极生寒。
Extreme Yin generates Yang; extreme Yang generates Yin. Things reverse at their extreme, cycling endlessly. Extreme cold generates heat; extreme heat generates cold.
「易穷则变，变则通」
易穷则变，变则通，通则久。
When the Changes reaches its limit, it transforms. Through transformation comes penetration. Through penetration comes duration.