This study examines Yi Ik and Jeong Yak-yong’s perspectives on nature, focusing on their discussions regarding the use and preservation of living beings. Their perspectives on living beings reflect a pragmatic acknowledgment of the need to utilize them for human purposes and a deep sense of responsibility for their preservation. In the Neo-Confucian worldview of liyifenshu (“One principle and many manifestations”), nature was traditionally regarded as an object of moral cultivation. However, Yi Ik and Jeong Yak-yong diverged from this framework by developing a post-liyifenshu perspective that redefined the view of nature. They shifted attention from nature as a moral subject to nature as a resource to be utilized. However, utilizing living beings in nature inherently entails the destruction of life. Yi Ik and Jeong Yak-yong addressed this issue by simultaneously treating living beings as objects of use and advocating for their preservation. However, their justifications and approaches to the use and conservation of living beings differ significantly. Yi Ik opposed the notion that nature exists solely for human benefit. Yet, he acknowledged the necessity of utilizing living beings, reflecting that human survival depends on nature. He sought to impose limits on the use of living beings by distinguishing between those that humans could harm and those that should be protected. However, Jeong Yak-yong justified using living beings based on the principle that nature exists for human purposes. However, he emphasized the responsibility of managing living beings, grounding this argument in his original theory of human nature. He further proposed the establishment of systems to ensure proper management of living beings. Yi Ik and Jeong Yak-yong’s discussions on using and preserving living beings exemplify a practical extension of the Confucian view of nature and represent one aspect of the Silhak (practical learning) inheritance of this tradition.