The “trolley” problem was introduced by Judith Jarvis Thomson in two papers, “Killing, Letting Die and the Trolley Problem,” and “The Trolley Problem” [Thomson, 1986; see also Foote, 1967]. The puzzle raised by the “trolley” problem is that of finding a principle that will reconcile two strongly held intuitions: that in the case of a trolley hurtling down the tracks towards five innocent persons, it is permissible to shunt the trolley onto a siding, thereby killing one person so that the five may live; while in the case of five patients requiring body parts, it is impermissible to anesthetize an innocent person and transplant the needed organs.

The problem is serious because the moral principle that most obviously seems to underlie the “trolley” case, viz., it is permissible to kill one in order to save five, is the direct denial of the principle that seems to underlie the “transplant” case. Indeed, the two cases are often supposed to place sharply in contrast consequentialist and deontological moral principles. For, in “trolley” the greater good for the greater number seems to decide the case, whereas in “transplant,” the rights of the innocent trump the welfare of the patients. Like Thomson, other philosophers have sought a principle that will reconcile our intuitions about “trolley” and “transplant.” Optimally, such a principle should explain why there is almost universal agreement on the two cases – that killing the one to save the five is permissible in “trolley” and impermissible in “transplant” and justify the moral distinction that we draw between them.