In the late Chosŏn period, Oeam and Namdang, two leading Korean Confucian scholars, were engaged in a heated debate over our unaroused state of mind (Ch. weifa, K. mibal 未發), or the original state of our mind before feelings are stirred. Although both scholars derived their arguments from the original propositions by Zhu Xi, their varying emphases led to a difference in their theoretical stances. This article analyzes the different arguments put forward by Oeam and Namdang concerning the definition of weifa, the relations between sim 心 (mind), sŏng 性 (nature), li 理 (principle), and ki 氣 (psycho-physical matter), and whether our sim is one and unified. Oeam based his theory on the differentiation of weifa into two kinds, namely the "great root" weifa and the "non-equilibrium" weifa—a dichotomy criticized by Namdang, who insisted on a "one and unified" weifa. These different claims reflected the varying positions these two Chosŏn thinkers took on the theoretical spectrum.