Some might think the thoughts of moral theologians quite beside the point when the topic at hand is the philosophy of homicide. What has moral theology to do with the philosophy of law? It might seem strange but theologians were the fi rst to systematize a logic of killing. It is a logic, moreover, that has guided Western culture for hundreds of years. Simply read the section on homicide in Blackstone’s commentaries on the common law alongside Aquinas’ question on killing in the Summa theologica (ST II-II, q. 64, aa. 1-8) and my point is obvious.1 Peter Singer agrees. Drawing up his own battle lines, Singer demands a new logic of killing because our homicide laws are sectarian, relying on “the distinctively Christian idea of the sanctity of all human life” (AL, 198; PE 77 & 125). Another reason the philosophy of law should concern itself with theology is that theology just won’t go away.2 To the horror of many perhaps, theology keeps obtruding into debates about killing, and the popes just won’t stay silent either.