BaZi Concepts
What Are the Four Pillars (Si Zhu) in BaZi?
Also called: Si Zhu, Sizhu, BaZi, Eight Characters
Plain Explanation
The Four Pillars are the four Stem–Branch pairs for the year, month, day, and hour. Each pillar contains one Heavenly Stem and one Earthly Branch. Together they contain eight characters, which is why the system is called BaZi, or Eight Characters.
Example
This diagram shows only the upper and lower positions of Heavenly Stems and Earthly Branches within the Four Pillars. It does not represent a person’s complete birth chart.
Year
Month
Day
Hour
What It Is Used For
The Four Pillars record the birth time as a set of Stem–Branch pairs and provide the basic information for BaZi analysis. Identifying the Day Master, the Month Command, and how the different Stems and Branches work together all begins with these four pairs.
Common Misunderstandings
The Four Pillars are not four individual characters
The year, month, day, and hour each form a pillar. Every pillar contains two characters: a Heavenly Stem above and an Earthly Branch below.
Related Concepts
Updated 2026-10-16 · Editorial Policy