Students of Chinese intellectual history are familiar with moral cosmology developed in the Han era, a theory that alleges that ru use omens to admonish the emperor, and thereby to constrain and compete with his absolute political power. This thesis, in theory, is convincing; in actuality it is not. This article questions the autonomous power of omen discourse. Focusing on the socio-political conditions in which this discourse functioned, it demonstrates that, in real politics, the enactment of omen interpretation had nothing to do with restraining the power of the throne, but evolved with bloody factional struggles. Replacing the secret knowledge of diviners and astrologers with the common cultural heritage—the classics—and transforming the mysterious otherworldly spirits into a moral agent, ru successfully defeated the technical specialists and became the primary operators of the omen interpretation enterprise. The theoretical innovation that contributed to ru's success, however, undermined their chance of building a social closure both to close off competition and to secure their interpretative authority. As numerous historical cases show, neither the ru classics nor the moral competence of the speaker add to the social efficacy of omen explanation: without monopolised knowledge, standardised hermeneutic rules, or institutionalised positions, omen discourse, rather than contesting political power, became its servant.