 Reasoning by appeal to cases is also a favorite mode of some recent moral philosophers. Since our focus here is not on the methods of moral theory, we do not need to go into any detail in comparing different ways in which philosophers wield cases for and against alternative moral theories. There is, however, an important and broadly applicable point worth making about ordinary reasoning by reference to cases that emerges most clearly from the philosophical use of such reasoning. Philosophers often feel free to imagine cases, often quite unlikely ones, in order to attempt to isolate relevant differences. An infamous example is a pair of cases offered by James Rachels to cast doubt on the moral significance of the distinction between killing and letting die, here slightly redescribed. In both cases, there is at the outset a boy in a bathtub and a greedy older cousin downstairs who will inherit the family manse if and only if the boy predeceases him (Rachels 1975). In Case A, the cousin hears a thump, runs up to find the boy unconscious in the bath, and reaches out to turn on the tap so that the water will rise up to drown the boy. In Case B, the cousin hears a thump, runs up to find the boy unconscious in the bath with the water running, and decides to sit back and do nothing until the boy drowns. Since there is surely no moral difference between these cases, Rachels argued, the general distinction between killing and letting die is undercut. “Not so fast!” is the well-justified reaction (cf. Beauchamp 1979). Just because a factor is morally relevant in a certain way in comparing one pair of cases does not mean that it either is or must be relevant in the same way or to the same degree when comparing other cases. Shelly Kagan has dubbed the failure to take account of this fact of contextual interaction when wielding comparison cases the “additive fallacy” (1988). Kagan concludes from this that the reasoning of moral theorists must depend upon some theory that helps us anticipate and account for ways in which factors will interact in various contexts. A parallel lesson, reinforcing what we have already observed in connection with casuistry proper, would apply for moral reasoning in general: reasoning from cases must at least implicitly rely upon a set of organizing judgments or beliefs, of a kind that would, on some understandings, count as a moral “theory.” If this is correct, it provides another kind of reason to think that moral considerations could be crystallized into principles that make manifest the organizing structure involved. 