This book is studying of purpose of Yehak(禮學) through Sagye Kim Jang-saeng, representative scholar of this studying in Chosŏn period. It also investigates the relation between Four Beginnings and Seven Emotions of Human Behavior, Sadan ch’iljŏng discussed largely in Confucianism and Yehak. That is, this examines how Explanation of the Original Nature and the Psychophysical Nature(理氣論) is applied as the theoretical of Yehak. In addition, we can see the core of debate about Yesong(禮訟) discussed since Sagye. The author says that we can solve the problem of royal descendants through the Chŏt'ongguan key point of view of Yehak.