Abstract
Objective : Heavenly stems and Earthly branches is a tool used for understanding the virtue of Yin Yang and Five elements. Korean medicine understands the changes in Wuyun through the Ten Heavenly stems, and understand the changes of Liuqi through the Twelve Earthly branches. An accurate understanding of the definitions of Heavenly Stems and Earthly branches and the concept of each of the 10 stems is of vital importance. Method : The paper first reviews the origin, history, and significance of the Heavenly stems and Earthly branches before studying the definitions of the stems and branches as laid out in the works of Yu Onseo, Lee Samun, and Han Dongseok. The paper then reviewed the concept of the each of the ten stems through researching the texts of Seoulmunhaeja, the annotations of the four great Seolmuns, and the texts of Jeongyeokwonui. Result & Conclusion : Heavenly stems and Earthly branches have been in use since more than 6,000 years ago. The central numbers in the changes of Heaven and Earth are five and six. Each number functions with duality, yin and yang, meaning there are ten Heavenly numbers ($5{\times}2=10$) and 12 Earthly numbers ($6{\times}2=12$) which oversees all of the cosmic changes. Stems become the body and signifies water. Branches become the use and signifies divided fire. The meanings of the letters Gab Eul Byeong Jeong Mu Gi Gyeong Sin Im Gye originate from the one year life of a tree which grows, bears fruits, processes Yang qi, and awaits for the next spring. The reason a tree is used is because there is nothing better in studying in detail the changes of a living being through a year.