Yi I (1536-1584) pen name Yulgok, is a distinguished scholar in the Korean Confucianism. With Yi T'oegye (1501-1570), he led the renaissance of Choson Neo-Confucianism in the sixteenth century. Through conducting in-depth study on Zhu Xi's Philosophy and critically embracing T'oegye's philosophy and Huadam's philosophy, Yulgok developed several philosophical thoughts: "Ii" is universal and "ki" is particular; "ki" is manifest and "Ii" rides on it; seven feelings include four beginnings; transforming psychophysical form. With suggestion that "Ii" is universal and "ki" is particular, Yulgok established a basis for the theory that human nature and things nature are same or different in the Choson Nco-Confucianism. From the perspective that "Ii" is universal, he claimed that human nature and things nature are same. From the perspective that "ki" is particular, he argued that human nature and things nature are different. According to Yulgok, human being and things are different not only in the purity of psychophysical form or in the presence of five virtues but also in the ability to change psychophysical form. From the perspective of self-cultivation, both sage and mediocrities are able to restore original nature through practice but the inferior are unable to do so. After Yulgok passed away, the debate that human nature and things nature are same or different in the Choson Neo-Confucianism began to diverge on the question of how to interpret Yulgok's Philosophy.