Yi Hwang, known by his pen name T'oegye, was the foremost Joseon-dynasty interpreter of Zhu Xi's Neo-Confucian metaphysics. In an extended correspondence with Ki Daeseung known as the Four-Seven Debate, he argued that the Four Beginnings (the sprouts of moral feeling) issue from principle (li) itself while the Seven Emotions issue from vital force (qi), giving li an active role that more monistic readers of Zhu Xi denied it. He distilled a lifetime of study into the Ten Diagrams on Sage Learning, presented to the young King Seonjo as a curriculum for moral self-cultivation.
Intellectual setting
T'oegye lived through the mid-Joseon dynasty's consolidation of Neo-Confucianism as state orthodoxy, serving intermittently at the royal court in Hanseong before repeatedly resigning to teach and study at his family's rural estate near Andong, where he later founded the Dosan Seodang academy; his career unfolded amid factional politics among the Joseon literati (sarim) elite.
Key ideas
The Four-Seven Debate: principle also "issues"
In correspondence with Ki Daeseung, T'oegye argued that the Four Beginnings (commiseration, shame, deference, and the sense of right and wrong) originate in principle (li) itself, while the Seven Emotions originate in vital force (qi) - a departure from more monistic readings of Zhu Xi that gave principle itself an active, "issuing" role in moral feeling.
The Ten Diagrams on Sage Learning
T'oegye's Seonghak sipto (1568), presented to King Seonjo, distilled Neo-Confucian cosmology, ethics, and self-cultivation practice into ten diagrams meant to guide a ruler's - and any student's - progress toward sagehood through reverent seriousness (kyeong).
Legacy
T'oegye's synthesis was so influential that Japanese Neo-Confucian scholars such as Yamazaki Ansai ranked him alongside Zhu Xi himself, and the Ten Diagrams became one of the most copied and studied texts of the Joseon dynasty; his Four-Seven Debate with Ki Daeseung, continued by later thinkers including Yi I, defined the central metaphysical fault line of subsequent Korean Neo-Confucianism.