Heavenly Stems (天干)

The Ten Heavenly Stems (天干) are: 甲乙丙丁戊己庚辛壬癸 (Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui). They cycle in pairs of Yin and Yang, each paired with one of the Five Elements:

• 甲乙 (Jia/Yi) — Wood (Yang/Yin)
• 丙丁 (Bing/Ding) — Fire (Yang/Yin)
• 戊己 (Wu/Ji) — Earth (Yang/Yin)
• 庚辛 (Geng/Xin) — Metal (Yang/Yin)
• 壬癸 (Ren/Gui) — Water (Yang/Yin)

Yang stems are outward, active, and direct. Yin stems are inward, receptive, and nuanced. In a BaZi chart, the stems represent the visible, conscious aspect of each pillar.