 Chŏng’s shorter rebuttal of Buddhism, On Mind, Material Force and Principle (Simgiri p’yŏn: 45–53), already highlights this intellectual nexus which dominates Neo-Confucianism in Korea. It introduces the main metaphysical issues that were of great importance in Korea at this time, namely, the mind (心; also referred to in literature as the heart-and-mind), the material force (氣), and of course Principle (理), which he describes as “the inherent virtue of the mind and that through which material force is produced”, and clearly states that “only after there is principle is there material force” (Simgiri p’yŏn: 50). He discusses what he considers to be the misinterpretation and application of ideas in the teachings of the Buddhists and Daoists, vindicating his rebuttal with quotes from the Mencius, the Analects, and the writings of Zhu Xi, as well as the Book of Rites. Chŏng’s arguments culminate in a radical espousal of Confucianism as an exclusivistic discourse, and he lauds the practical and direct social implications of these metaphysical ideas, juxtaposed to Buddhist and Daoist emphasis on emptiness and vacuity, which he considers to be devoid of meaning when related to matters of the mundane world (Simgiri p’yŏn: 53). The philosophical implications of Chŏng’s ideas are related to this-worldly affairs and not speculative spiritual proclivities of other traditions, which he suggests depended on deities who could then reward or punish. Chŏng asserts the need to investigate one’s human nature and the mind for oneself, and not to rely on teachings that call upon spirits to do so, advocating the Confucian practice of preserving what is good in the mind and nourishing the material force to control bodily desires through proper Confucian education (Simgiri p’yŏn: 51). This bifocal approach would become greatly elucidated by later Neo-Confucian philosophers who would advocate an approach to fully develop the humanity (K. in) that our minds were “naturally” endowed with by Principle.