The ancient Yin-Yang principle constructed a fantastic system of 10 heavenly stems and 12 earthly branches, the latter corresponding to 12 animals with two symbolic functions.
Heavenly stems and earthly branches are collectively known as Stem-Branch or Gan-Zhi. The 10 heavenly stems are Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren and Gui.
The ten heavenly stems are a process of the growth of all things. For example, Jia(甲) is like the seed just budding, like grass sprouting. Yi(乙) is like the grass and trees are bent after they grow. Bing(丙) is like the grass that grows lusher after it grows.
The heavenly stem is also like a person, Jia is the head, Yi is the neck, and Bing is the shoulder. Ding is the heart. The heart and small intestines are considered to have the same energetic qualities and are seen as a pair, and are connected to the fire element.
Wu is the ribs and stomach, and Ji is the spleen and belly. The organs related to the earth’s elements are the Spleen and the Stomach.
Geng is the navel. Xin is the thigh. Ren is the shank and Gui is like the feet. The ten heavenly stems are exactly like the part from the head to the foot of the human being. When a newborn comes out of the womb, it is also in the order of head to toe. This is very interesting.
The 12 earthly branches are Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai. Looking at the twelve earthly branches also represents a process in which everything begins to be born, grow up and die. For example, Zi is when everything just starts to breed, and Chou is when things start to move, and they move more strongly. At the time of Yin, the yang energy is activated and begins to emerge, and at the time of Mao, all things come out from the ground. This is a process, and it is also like a person. For example, Zi is like a person still in the womb, Chou is like a hand, and Yin is like a kneecap.
It can be seen that the Heavenly Stems and Earthly Branches represent the process of growth and movement of all things in nature, and it is also order and pattern. This pattern can also be represented by the five elements. The order of five elements is arranged according to the spring, summer, autumn and winter of a year.
Wood, fire, earth, metal, and water correspond to spring, summer, later summer, autumn, and winter. The ten heavenly stems are matched with the five elements: Jia and Yi are wood, Bing and Ding are fire, Wu and Ji are earth, Geng and Xin are metal, and Ren and Gui are water, which also corresponds to spring, and summer, long summer, autumn and winter.
10 Heavenly Stems and corresponding representations
| 10 Heavenly stems | Five elements | Representation |
| Jia | Yang Wood |  |
| Yi | Yin Wood |  |
| Bing | Yang Fire |  |
| Ding | Yin Fire |  |
| Wu | Yang Earth |  |
| Ji | Yin Earth |  |
| Geng | Yang Metal |  |
| Xin | Yin Metal |  |
| Ren | Yang Water |  |
| Gui | Yin Water |  |
Looking at the matching of the 12 Earthly Branches and the five elements: Yin and Mao belong to the element of wood, Si and Wu belong to the element of fire, Chen, Xu, Chou, and Wei belong to the element of earth, Shen and you belong to the element of mental, and Hai and Zi belong to the element of water.
12 Earthly Branches and corresponding representations
| 12 Earthly Branches | Five elements | Representation |
| Zi | Yin Water | |
| Chou | Yin Earth | |
| Yin | Yang Wood | |
| Mao | Yin Wood | |
| Chen | Yang Earth |  |
| Si | Yang Fire | |
| Wu | Yin Fire | |
| Wei | Yin Earth | |
| Shen | Yang Metal | |
| You | Yin Metal |  |
| Xu | Yang Earth |  |
| Hai | Yin Water | |