The Korean Neo-Confucianism of Yi Toegye and Yi Yulgok (Part 148)
As toegye argued in his Four-Seven letters to Kobong, Heaven’s principle refers to what Mencius called the original goodness of human nature, what the Doctrine of the Mean called the original goodness of human nature, what the Doctrine of the Mean called human nature endowed by Heaven, or what Chang Tsai and Chu Hsi meant by original human nature. In his Songhak sipto, Toegye also asserts that it implies what Cheng I and Chu Hsi meant by human nature is i and what Chang Tsai and Chu Hsi referred to as the nature of Heaven and Earth. All of these phrases mean the Four Beginnings, not the Seven Emotions, referring to “i in itself” or the “original essence of human nature.” Of course, Heaven’s principle pertains to the genuine source of moral self-cultivation. As Toegye told Kobong, One’s unwillingness not to distinguish i from ki means to misidentify the moral qualities (like the Four) aroused by Heaven’s principle with the selfish human desires (like the Seven) aroused by external stimuli.
By citing Chen’s Hear Classic, Toegye articulates his position on the Cheng-Chu learning of the mind-and-heart in the following words: “Simhak is…none other than two ideas such as suppressing human desires to the work of the human mind, and to preserve Heaven’s principle belongs to the work of the moral mind. If not so, why would Chen Tu-hsiu concluded at the end of his Heart Classic that ‘overcoming and controlling’ and ‘preserving and nourishing’ both help one’s effort at simhak?” For Toegye, then, the Cheng-Chu simhak should be based on the suppressing and overcoming of the human mind and the preserving and nourishing of the moral mind. However, a relevant question arises here, How does such a way of simhak relates to his Four-Seven thesis in terms of human nature (song) and feelings (chong)?