Yu Sung-jo’s Theory of Heart-Mind and Nature

Yu Sung-jo’s Daehakjam was greatly influenced by Kwon-Geun’s Iphak doseol, and his Seongli yeonwon chwaryo actively utilized Cheng Fuxin’s Sishu zhangtu, etc. In Zhuzi, the heart-mind is synchronically explained to be composed of li and qi and diachronically encompasses xing and qing. Yu Sung-jo understood heart-mind in the perspective of mingde 明德 as a whole, meaning that the heart-mind in reality is only a state that has not fully maintained its mingde, and its essence is the same as mingde. All living beings have heart-mind, but the characteristics of the human mind are specifically called mingde. The heaven is composed of li and qi, and all things created by the heaven is originally composed of the same li and qi, and among them, the heart-mind of human is more clever than any other, and xuling bumei 虛靈不昧 that only human possesses is called mingde, which is also called benxin. When it is said that the heart-mind is composed of xing and qizhi, there is an inherent commonality in the disposition that constitutes human’s mingde that distinguishes it from other living beings. However, qizhi of each person is different, and thus the state of mingde varies greatly. Yu Sung-jo emphasized the view of dividing xing into benranzhixing 本然之性 and qizhizhixing 氣質之性, and established the theory that the origin of the Four Sprouts is benranzhixing and the origin of the Seven Emotions is qizhizhixing. Yu Sung-jo also established a way of explaining both the Four Sprouts and the Seven Emotions in a way that combines li and qi. Yu Sung-jo’s academic system contributed greatly to shaping the common sense view of Zhuzi in later generations through the education at Sungkyunkwan, and may have had some influence on Toegye’s theory of Four Sprouts and Seven Emotions.