How the Trolley Problem Works

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.

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.