The scholarly pursuits of Yi Hwang can be evaluated as the lihak (理學), as he placed a significant emphasis on theoretical discussions centered around li (理). This work was conducted after Yi Hwang started to focus on teaching activities in 1550. Although multiple factors contributed to the formation of Yi Hwang's lihak, the author would like to highlight that, since the early 1500s, Yi Hwang actively participated in academic discussions with the scholar, Seo Gyeong-deok, and others. Through these academic discussions, Yi Hwang came to realize that Seo's theories only explained the origin, formation, and change of all things in the universe based on Gi (氣) and neglected li. During his discussions with Seo Gyeong-deok and other scholars, Yi Hwang recognized the need to complement Seo Gyeong-deok's monistic theory of gi. In his philosophical discussions, Yi Hwang emphasized the existence and role of li, which he believed was distinct from gi. He achieved this through several means: ① explaining the human world from the perspective of li, ② revealing the role of li in forming emotions in the Four Beginnings, through the Manifestation of Li, and ③ emphasizing the unique role of li in forming the phenomenal world, through his assertion that Li also has a function. The debates surrounding the distinct ontological status of li and gi stem from a critical examination of Seo Gyeong-deok's monistic theory of gi. This interaction between Seo Gyeong-deok and Yi Hwang was a crucial factor in shaping the latter's perspectives on li. Yi Hwang's academic approach, which centered on the existence and significance of li separate from gi, laid the foundation for his proposition Li arrives on its own, in his later years. Thus, his critical examination of Seo Gyeong-deok's theory played a vital role in enabling him to form the lihak hrough extensive theoretical discussions and emphasizing its importance.