Some of Philo’s most explicit descriptions of how humans can properly perceive God occur in his allegorical exegesis of Genesis 4 (esp. Det. 86–90; Post. 13–20, 158–69). These positive accounts, affirming the possibility of human perception of God through divine aid, are set in a negative frame, Cain’s slaughter of Abel and departure from God. This essay explores the negative frame. What might Cain teach about Philo’s criteria for the impossibility of perceiving God? I argue that Philo portrays Cain as the quintessential evil man, unable to perceive God because of self-inflicted disorder. Two passages in particular are notable examples of Philo interpreting Cain as a type for the person unable to perceive God. First, in Det. 75–78 Philo argues that by slaughtering his brother, Cain has destroyed the expression of the idea of virtue available to him. Philo’s “seal” and “impression” language evokes the concept of the “Law of Nature” and Plato’s theory of forms. The Law is available to Cain through his virtuous brother, but Cain’s slaughter of Abel destroys the embodiment of the Law. In this way Cain becomes “his own murderer.” Second, in Post. 8–11 Philo interprets Cain’s departure from God’s presence as necessarily figurative, with Cain’s departure understood as a voluntarily blinding to a vision of God. Philo contrasts Cain’s voluntary departure with Adam’s involuntary expulsion from God’s presence. The voluntary departure is described using the Platonic phrase “eye of the soul,” which has been “maimed” by Cain, making him incapable of perceiving God. Analyzing Philo’s portrait of Cain in Det. 75–78 and Post. 8–11 reveals the self-imposed conditions under which the Alexandrian considers it impossible for humans to develop a proper conception of God.