阴阳
polarity — the first distinction
Everything in 八字 begins with one cut: the world divides into 阳 yáng and 阴 yīn. The characters themselves draw the picture. 陽 (traditional form) is a hill 阝 with the sun 日 shining on it — the lit side, the exposed slope. 陰 is the same hill under a cloud — the shaded side, the hidden slope. Same hill, two faces. That is the whole doctrine in one image: polarity is not a ranking of things, it is the two faces of one thing.
In the chart, polarity is a grammar of rhythm. Every one of the ten stems and twelve branches is either yang or yin — they alternate, the way day alternates with night. Polarity decides nothing by itself, but it tunes everything else: it splits the 十神 into 正 and 偏 (module 7), it sets the direction of your 大运 (module 14), and it gives each character its texture.
the two strokes of the brush — 阳 与 阴
Yang is the outward stroke: movement, initiation, expansion, heat, day, the visible. Yin is the inward stroke: rest, reception, contraction, coolness, night, the hidden. Neither is better. A lung does both — one beat out, one beat in. A life does both — seasons of pushing and seasons of waiting. The tradition reads them as complements, not competitors.
Two cautions the tradition itself insists on. First, yin-yang is not the western "good versus evil" — a yin stem is not a dark force, and a yang stem is not a virtue. Second, it is not a gender essentialism: yang and yin appear in every person and every chart in shifting proportions. Anyone who uses polarity to rank people has left the doctrine and started fortune-telling.
the four degrees — 太阴 少阴 少阳 太阳
The tradition does not stop at two. Each pole splits again: 太阳 tài yáng (great yang, midday), 少阴 shào yīn (young yin, evening), 太阴 tài yīn (great yin, midnight), 少阳 shào yáng (young yang, dawn). These four degrees are the ancestor of the 五行 phases — the day understood as a circle, not a line. In the chart they appear indirectly: the twelve branches are the four degrees folded three times over.
polarity in your chart
In the app, polarity appears on every character card: each stem and branch shows 阳 or 阴. A chart can run all-yang, all-yin, or any mix. The tradition reads the mix as texture — a chart heavy in yang reads as outwardly driven; heavy in yin reads as inwardly drawn. That is a description of style, not a sentence about worth. Count yours, notice the balance, and move on: polarity is the drumbeat, not the song.