Until the early twentieth century, it was widely believed that a systematic body of moral knowledge was possible, and necessary for guiding human life. But in the early twentieth century this attitude disappeared, first from the culture in general and then from the institutions traditionally thought responsible for moral knowledge. The institutional and cultural situation resulting from this change of attitude is the disappearance of moral knowledge. This chapter argues that the disappearance was not grounded in any demonstration or discovery to the effect that that moral knowledge is unreal or unattainable, but that it resulted from a number of nonrational social and historical factors. It further argues that the resulting situation is highly undesirable because, when knowledge in any domain disappears, that domain becomes subject to nonrational forces—baseless beliefs and undisciplined desires and motives—which frequently lead to disaster. All of this is illustrated by tracing the disappearance of moral knowledge and its effects in the context of the institution once thought to be most responsible for it—the university.