이이
Master Yi I was not only known as a philosopher but also as a social reformer. He did not completely agree with the dualistic Neo-Confucianism teachings followed by Yi Hwang. His school of Neo-Confucianism placed emphasis on the more concrete, material elements; rather than inner spiritual perception, this practical and pragmatic approach valued external experience and learning. Unlike Yi Hwang, who suffered through tumultuous times and did not enjoy being in politics, Yi I was an active official who thought it important to implement Confucian values and principles to government administration. He emphasized sage learning and self-cultivation as the base of proper administration.