Would you pull a switch that sent a man to his death to save five others on a runaway trolley?

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How the Trolley Problem Works

It's a lovely day out, and you decide to go for a walk along the trolley tracks that crisscross your town. As you walk, you hear a trolley behind you, and you step away from the tracks. But as the trolley gets closer, you hear the sounds of panic -- the five people on board are shouting for help. The trolley's brakes have gone out, and it's gathering speed.

You find that you just happen to be standing next to a side track that veers into a sand pit, potentially providing safety for the trolley's five passengers. All you have to do is pull a hand lever to switch the tracks, and you'll save the five people. Sounds easy, right? But there's a problem. Along this offshoot of track leading to the sandpit stands a man who is totally unaware of the trolley's problem and the action you're considering. There's no time to warn him. So by pulling the lever and guiding the trolley to safety, you'll save the five passengers. But you'll kill the man. What do you do?

Consider another, similar dilemma. You're walking along the track again, you notice the trolley is out of control, although this time there is no auxiliary track. But there is a man within arm's reach, between you and the track. He's large enough to stop the runaway trolley. You can save the five people on the trolley by pushing him onto the tracks, stopping the out-of-control vehicle, but you'll kill the man by using him to stop the trolley. Again, what do you do?

Both of these grave dilemmas constitute the trolley problem, a moral paradox first posed by Phillipa Foot in her 1967 paper, "Abortion and the Doctrine of Double Effect," and later expanded by Judith Jarvis Thomson. Far from solving the dilemma, the trolley problem launched a wave of further investigation into the philosophical quandary it raises. And it's still being debated today.

The trolley problem is a question of human morality, and an example of a philosophical view called consequentialism. This view says that morality is defined by the consequences of an action, and that the consequences are all that matter. But exactly which consequences are allowable?

Take the two examples that make up the trolley problem. On the surface, the consequences of both actions are the same: one person dies, five survive. More specifically, in both examples five people live as the result of one person's death. At first, both may seem to be justified, but most people, when asked which of the two actions is permissible -- pulling the lever or pushing the man onto the tracks -- say that the former is permissible, the latter is forbidden [source: Greene]. It reveals a distinction between killing a person and letting a person die.

Why is one wrong and another possibly allowable when both result in death? It's a question of human morality. If a person dies in both scenarios, and both deaths directly result from an action you take, what's the distinction between the two? Aside from that highly improbable moment when you actually find yourself near a big man and a runaway trolley and think, "Wow, I'm glad I read that article on HowStuffWorks," the trolley problem seems far-fetched. But philosophical questions like this have real-world implications for how people behave in society, governments, science, law and even war.

The trolley problem is based on an old philosophical standard called the Doctrine of Double Effect. Read about that on the next page.

St. Thomas Aquinas, the 13th-century philosopher who established the Doctrine of Double Effect.

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The Double Effect

The trolley problem presents a case of two similar, but vastly different moral dilemmas. Those who subscribe to the philosophical theory of utilitarianism would say that both are justified. Utilitarianism is a no-frills view of consequences. If the outcome for five people is good and the outcome is bad for one, the action is justified, permissible and even obligatory.

That gnawing little feeling you get in the back of your head when you consider the consequences of pushing a man in front of a trolley is expressed in the Doctrine of Double Effect. This notion, first introduced by St. Thomas Aquinas in the late 13th century, gives a name to the reason we have trouble accepting that it's OK to push the man onto the tracks.

This doctrine says that for an act to be morally permissible, it has to fit certain criteria. For starters, the outcome has to be a good one. Both examples in the trolley problem have that -- five people survive a terrible accident. Secondly, the outcome has to be at least as important as the action taken. Both examples cover that, too -- five lives outweigh one. Thirdly, the action can't be taken for the purposes of evil, even if it does result in beneficial good. In other words, you can't pull the lever just because you want to kill the man standing in front of the sand pit.

Lastly, the good effect has to be produced by the action taken, not by the bad effect. And here we reach the reason why pulling the switch is preferable to pushing the man onto the tracks. By pulling the lever, we are taking an action that indirectly results in the death of the man on the track. In the second example, we are intentionally pushing the man to his death. Although five people's lives will still be saved, according to Aquinas (and to many philosophers), an evil act never justifies a greater good.

Aquinas used the example of self-defense to prove his argument. As long as the victim's intent is to save his or her own life (a good intent) and not to kill his or her attacker (an evil intent), then self-defense, he reasoned, is justified and allowable [source: Stanford Encyclopedia of Philosophy].

Although Aquinas lived 700 years ago, his views on human morality are a cornerstone of Western legal systems. Even today, defendants who can prove they killed a person in self-defense are acquitted.

The Doctrine of Double Effect is based on Aquinas' observations of human morality. But where does it come from? Read the next page to find out how science is looking into our brains to uncover the source of our knowledge of right from wrong.

Joshua D. Greene uses MRIs to discover what parts of our brains are responsible for morality.

Courtesy Joshua Greene

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The Biology of Morality

One school of thought, established by German philosopher Immanuel Kant, believes that our sense of morality is connected to reason. Pulling a lever and incidentally killing a man on the side track is worth it if it saves five lives. Conversely, it's wrong to kill a person intentionally, so pushing the man onto the trolley tracks is immoral, even if it saves five others.

Early 21st century investigation suggests Kant's theory may not be correct. Primates in studies have been shown to understand principles of fairness and get angry when others in their groups behave selfishly. This undermines the idea of reason-based morality, since it's believed that high reasoning belongs to humans alone. And technology is also lending support to the idea that morality is ingrained in us.

Since its creation in the 1970s, magnetic resonance imaging (MRI) has been used for everything from finding tumors hidden deep within the brain to detecting whether or not a person is lying. Now, it's being used to discover which parts of our brains help us determine right from wrong.

Joshua Greene at Princeton University is leading the charge to explore morality through the use of technology. He's been using MRIs in conjunction with the trolley problem and other moral paradoxes. He's found that when a person in an MRI machine is asked questions like whether they should take a bus or a train to work, the parts of their brain that activate to form their answers are among the same areas that activate when the person is sorting through the first example in the trolley problem. The thought of pulling a switch that will dispatch one person to save five appears to be governed along the lines of reason and problem solving.

On the other hand (or region of the brain), Greene has found that distinctly different parts of the brain activate when people consider pushing a man onto the tracks. Regions that are responsible for determining what other people are feeling, as well as an area related to strong emotions, swing into action when a person is confronted with the decision of whether to push the man onto the tracks. It's possible this combination of brain functions constitutes our moral judgment.

Greene's not alone in his quest to update human morality. John Mikhail, a philosopher at Georgetown University, is investigating his belief that the brain handles morality in a similar way to how it handles grammar. In Mikhail's opinion, we decide if an act is moral or immoral based on a series of clues within the context. We recognize an act as immoral in the same way we recognize a grammatical error in a sentence -- it just stands out.

Morality, whether instinctual, as Mikhail believes, or exclusively carried out by neural functions, remains elusive. But once science determines exactly how morality works, a question will still remain: Why do we have morality?

To learn more about morality, philosophy and other related topics, see the links on the next page.

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Sources

  • Greene, Joshua D. "The terrible, horrible no good very bad truth about morality and what to do about it." Princeton University. June 2002. http://www.wjh.harvard.edu/~jgreene/GreeneWJH/Greene-Dissertation.pdf
  • Mikhail, John, et al. "Toward a universal moral grammar." Proceedings of the Twentieth Annual Conference of Cognitive Science Society. 1998. http://www.law.georgetown.edu/faculty/mikhail/documents/ Toward_a_Universal_MoralGrammar_pdf.pdf
  • Saxe, Rebecca. "Do the right thing." The Boston Review. September/October 2005. http://bostonreview.net/BR30.5/saxe.html
  • Swartz, Luke. "Silicon at the Switch: A Computational Moral Grammar for Solving Trolley Problems." Stanford University. 2000. http://xenon.stanford.edu/~lswartz/trolley/
  • Zimmer, Carl. "Whose life would you save?" Discover Magazine. April 21, 2004. http://discovermagazine.com/2004/apr/whose-life-would-you-save
  • "Doctrine of the Double Effect." Stanford Encyclopedia of Philosophy. July 28, 2004. http://plato.stanford.edu/entries/double-effect/
  • "John Harris on the 'survival lottery'." Minnesota State University Moorehead. August 29, 2005. http://www.mnstate.edu/gracyk/courses/phil%20115/ Harris_on_Survival_Lottery.htm