The problem of “the morally bad” (e )1 has been a central issue for Confucianism ever since Mengzi claimed that “human nature is good” (xing shan ). Xunzi took an opposing position and attributed moral badness to human nature, attempting to account for the phenomena of mutual conflict and confusion among human beings by their innate tendencies and desires.2 However, those who find Mengzi’s view more appealing have to face a particular challenge: If the human nature is good, why the morally bad exists? Furthermore, Mengzi considers that the “heart-mind” (xin ) is a transcendental ground for morality which makes moral goodness possible; he has to deny justifiably the factors which cause moral badness function dominantly. This challenge is particularly urgent for Neo-Confucians, since some of their metaphysical assertions provide support for the transcendental ground mentioned above, therefore it seems that it is more difficult to explain the existence of the morally bad. This fact though makes it particularly interesting to explore the ways that Neo-Confucians have taken to address this problem. In this article I shall focus on examining the Cheng Brothers’3 approach to tackling this issue.