On Twin Earth, a brain in a vat is at the wheel of a runaway trolley, approaching a fork in the track. The brain is hooked up to the trolley in such a way that the brain can determine which course the trolley will take. There are only two options: the right side of the fork, or the left side. There is no way to derail or stop the trolley, and the brain is aware of this. On the right side of the track there is a single railroad worker, Jones, who will definitely be killed if the brain steers the trolley to the right. If Jones lives he will go on to kill five men for the sake of thirty orphans (one of the five men he will kill is planning to destroy a bridge that the orphans’ bus will be crossing later that night). One of the orphans who will be killed would have grown up to become a tyrant who made good, utilitarian men do bad things, another would have become John Sununu, a third would have invented the pop-top can.
If the brain in the vat chooses the left side of the track, the trolley will definitely hit and kill another railman, Leftie, and will hit and destroy ten beating hearts on the track that would have been transplanted into ten patients at the local hospital who will die without donor hearts. These are the only hearts available, and the brain is aware of this. If the railman on the left side of the track lives, he, too, will kill five men—in fact, the same five that the railman on the right would kill. However, Leftie will kill the five as an unintended consequence of saving ten men: he will inadvertently kill the five men as he rushes the ten hearts to the local hospital for transplantation. A further result of Leftie’s act is that the busload of orphans will be spared. Among the five men killed by Leftie is the man responsible for putting the brain at the controls of the trolley. If the ten hearts and Leftie are killed by the trolley, the ten prospective hearttransplant patients will die and their kidneys will be used to save the lives of twenty kidney transplant patients, one of whom will grow up to cure cancer and one of whom will grow up to be Hitler. There are other kidneys and dialysis machines available, but the brain does not know this.
Assume that the brains choice, whatever it turns out to be, will serve as an example to other brains in vats, and thus the effects of its decision will be amplified. Also assume that if the brain chooses the right side of the fork, an unjust war free of war crimes will ensue, whereas if the brain chooses the left fork, a just war fraught with war crimes will result. Furthermore, there is an intermittently active Cartesian demon deceiving the brain in such a way that the brain is never sure that it is being deceived.
Question: Ethically speaking, what should the brain do?
[ALTERNATIVE EXAMPLE: Same as above, except the brain has had a commisurotomy, and the left half of the brain is a consequentialist and the right side is an absolutist.]
(Michael F. Patton, "Can Bad Men Make Good Brains Do Bad Things?" Proceedings and Addresses of the American Philosophical Association, Vol. 61, No. 3 (Jan ., 1988), pp. 555-556)