The question of the origin of badness is a core problematic in New Confucian philosopher Xiong Shili’s 熊十力 (1885–1968) Ming Xin Pian 明心 篇 (Explaining the Mind; 1959), a work representative of his thought towards the end of his life. In this essay, I examine how Xiong uses the concepts of the nature (xing 性) and the mind (xin 心) to explain the origin of moral badness. Xiong asserts that the Buddhists never concerned themselves with the problem of the origin of ignorance and delusion, afflictions that in turn lead to suffering and wrongdoing. Xiong sets out to redress what he claims the Buddhists had failed to do. I argue that the conceptual structure of both Xiong Shili’s and Zhu Xi’s 朱 熹 (1130–1200) theoretical approaches to this problem are isomorphic. The isomorphism is significant because it suggests that Xiong consciously drew on Zhu Xi and/or the Buddhist models that Zhu in turn drew on. I provide evidence to show that even as late as 1959, and despite his increasingly entrenched criticisms of Buddhism, Xiong continued to draw on key concepts and models drawn from Buddhist philosophy of mind.