The four pillars are the cornerstones of Chinese astrology. Each year, month, day, and 2-hour period of each day is assigned a combination of one of the 12 animal signs (branches) and one of the 5 elements (stems).
Ba Zi means "eight words" or "eight characters," and denotes the one element and one animal sign in each of the four "pillars." Two characters (one of the five elements placed on top of one of the 12 animal signs) times four pillars or positions (one for your birth year, one for your birth month, one for your birth day, and one for your birth hour) equal the eight words.
These eight words (four elements and four animal signs) comprise what is called the four pillars of destiny, or Ba Zi. Here's an example:
Eight Characters, Four Pillars Ba Zi is a system of astrology invented by Li Xu Zhong in the Tang Dynasty (618-907 AD). The system was later revised and updated by Xu Zi Ping of the Song Dynasty (960-1279 AD). The most authoritative work is the San Ming Tong Hui by Wan Yu Wu of the Ming Dynasty (1368- 1644 AD).
As with each of the many forms of Chinese divination, the four pillars began with a hypothesis, which was then supplemented by and confirmed through observations and experimentation until a formula was found that returned reliable and consistent results. The ancient Chinese developed the art of four pillars of destiny as a method for understanding and enhancing our life experiences.