This thesis compares the “Dao Xin(道心,the way of heart and mind) and Ren Xin (人心,the human’s heart and mind) Theory” of Zhu Xi and Jeong Yakyong. The philosophical meaning of Zhu Xi’s “Dao Xin” is investigated through several steps. It first focuses on the consciousness of "Dao Xin" to examine the changes and the differences of philosophical meaning of the “Dao Xin”. The theoretical development of the old theory and the new theory of Zhong He(中和) is discussed as well to explain the “Dao Xin” further. The theories of Zhong He is brought up by Zhu Xi, from the debates between Cheng Yi and Lui Dalin on Zhong(中) and Weifa-Yifa(未發已發), which is analyzed additionally.
On the contrary, Jeong Yakyong’s theory is studied in different steps. First, Jeong Yakyong''s perspectives regarding the Catholicism is examined from the historical point of view. Secondly, Jeong Yakyong''s thoughts and viewpoints of the Shang Di is discussed with the similarity of the Catholic theory. Furthermore, Jeong Yakyong''s philosophical meaning of the Dao Xin and Ren Xin theory is analyzed in depth.
The comparison between Zhu Xi and Jeong Yakyong''s views on "Dao Xin" is conducted. (1) Zhu Xi''s "Dao Xin" is a moral consciousness that must be formed after "Perception". Zhu Xi does not actually give ontological meaning to the Dao Xin. (2) Jeong Yakyong''s "Dao Xin" is equivalent to the "Ling ming"(靈明) and "the nature of Tian Ming(天命,the nature of God''s will) as the representative noumenal ontology, and "God" (上帝) is the ultimate ontology on which these ontological meanings are based. Based on the all discussions above, the comparison between Zhu Xi and Jeong Yakyong''s ontology and practical theory is researched along at the end of this thesis.