Foundation
Yin and Yang
Two sides of all change: light and dark, moving and still, firm and soft.
陰陽者，天地之道也，萬物之綱紀，變化之父母，生殺之本始，神明之府也。
Su Wen
一陰一陽之謂道。
Xi Ci
What it is
Yin and yang are not good and evil. They are two sides of one thing. The sunny side of a hill is yang and the shaded side is yin, and as the day passes the two change places.
Su Wen calls yin and yang the way of heaven and earth, and Xi Ci says one yin and one yang is called the Way. Both put it ahead of everything else.
How to read it
Yang usually means moving, hot, bright and outward. Yin usually means still, cold, dark and inward. Change needs both.
In a chart
Every stem and branch is yin or yang. In the trigrams and hexagrams a solid line is yang and a broken line is yin.
Sources Su Wen; Xi Ci.