(provided by Derek from lisiming.com)
Yin-Yang and Bagua are abstract symbols used to represent different parts of the world and human life.
During the prehistorical era of Chinese cultivation, Fuxi, a legendary emperor in the Chinese civilization, constructed the Innate Bugua (先天八卦) which used Yin(- -) and Yang(—) lines to describe the eight phenomena of the world: i.e. Sky, Earth, Sun, Moon, Wind, Thunder, Mountain, River. These eight phenomena are represented by eight trigrams of Yin and Yang lines. During the Zhou Dynasty (12th century B.C.), Zhou Wen Wang (周文王) rearranged the Innate Bagua into the Acquired Bugua (后天八卦), using the same eight trigrams in Innate Bagua but in different positions with each other. Furthermore, he superimposed the eight trigrams and constructed the 64 trigrams which provide further descriptions of different phenomena of the world.
During the Autumn-Spring period (6th century B.C.), Laozi described that there is a changeless reality behind the changing phenomena, which represent the context out of which the dualistic nothingness (无) and existence (有) arise. Confucius then summarized the founding of Laozi, Fuxi, Zhou Wen Wang, and Yin-yang School (阴阳家) into his report in the Annex of YiChing (易经 – 系辞), which describes the various representation of the world as: Change consists of Taiji, Taiji gives birth to Two Opposites, Two Opposites gives birth to Four Phenomena, Four Phenomena gives birth to Eight Trigrams (易有太极, 是生两仪, 两仪生四象, 四象生八卦), which further divide into 64 Trigrams.
If we combine the findings from Laozi and Confucius, we arrive at the Daoist/Confucius view of the universe (Daoism and Confucianism were not separated at the time of Laozi and Confucius), which is described numerically as follows: 0: nothingness (wuji); 1: existence (taiji); 2: opposites (liangyi); 4: phenomena (sixiang); 8: trigram (bagua); 64 trigrams. Based on this system, ChenTuan (陈抟) and later scholars constructed the Taiji Diagram (太极图) which summarized the Daoist/Confucius view of the universe as follows:
On the left is Fuxi’s Innate Bagua, on the right is ZhouWenWang’s Acquired Bagua. In both diagrams, Yin-Yang represent the core elements in the centre, with white represents Yang and black represents Yin. Despite of being opposite, Yin and Yang are rotating into each other, and within Yang is a spot of Yin and vice versa, illustrating the ever-changing nature of the phenomenal world. If we further divide Yin-Yang in the center, we get Four Phenomena/Direction and then we get Eight Trigrams in the peripheral, which represents the different phenomena observable in the world. If we return inward to the center, from eight trigrams to four directions to Yin-Yang and transcend them, we arrive at Taiji/Dao, which represents the transcendence of all opposites/duality, the ultimate state in Daoist cultivation as described by Laozi in his book DaoDeJing.