Toegye and Yulgok are known as the two major leaders of Korean Confucianism. Due to ideological differences between the two, Korean Confucianism developed along two branches: the Youngnam School and Kiho School, each of which discussed Neo-Confucian concepts ranging from the taiji 太極、wji 無極 debate to the Four-Seven Debate and the discussion about the differences between the nature of human and non-human throughout the Choson dynasty. The core issue at stake during the era of Choson Confucianism was how to acquire power to practice moral conduct, a question which required a comprehension of Zhu Xi’s teaching regarding the issue of how to treat the subject of lifa 理發. Although Mou Zongsan considered Yulgok’s understanding of Zhu Xi to be more accurate, if we view the question as concerning the practical power to practice moral conduct, Toegye’s understanding of Zhu’s teaching may be more useful than that of Yulgok. Although Toegye’s understanding appears superficially similar to the school of Lu-Wang, Toegye regularly criticized the teachings of Lu-Wang. By comparing the views of Yulgok and Toegye as understood by Mou Zongsan, we will be able to see a number of important similarities and differences.