(Inspired by philosophyexperiments.com)
You are a surgeon. You have five patients, each needing a different kind of transplant, who will die if they don't receive them. However, they never personally paid you for the operation. Just when all hope seemed to be lost, a foreign backpacker walks into your hospital for a little checkup. He is in perfect health, and would be able to provide for all four of your patients, saving their lives (your transplantations are always perfect). He doesn't have any friends or family in the area, and in fact, there is no one in the country who knows he exists, so no legal harm would come to you. Will you kill him? Should you kill one man to save five?
Consequentialism: Yes. Morality aims to maximise pleasure and minimise suffering, and by simple arithmetic (considering equal happiness for everyone) we can see that there would be four times as much pleasure gained in the world if you killed the backpacker. In other words, an action can only be considered in terms of its consequences.
Deontology: No. A human being cannot be used as a means to an end, and if everyone did such gambits and killed people to save others, we would be much worse off. An act should be an end in itself, and the maxim used to justify it should apply to everyone, any time.
Liberalism: No. The backpacker would never consent to it. Besides, the patients never gave me any incentive to save them, and it was their responsibility to pay for their problems. The goal of morality is to maximise and individual's liberty, without infringing on others'.
Bookmarks