Would you push or not push?

Blood on the tracks
David Hume wrote that reason is a ``slave to the emotions." But new research suggests that in our moral decision-making, reason and emotion duke it out within the mind.
By Christopher Shea | August 6, 2006

MORAL PHILOSOPHERS and academics interested in studying how humans choose between right and wrong often use thought experiments to tease out the principles that inform our decisions. One particular hypothetical scenario has become quite the rage in some top psychological journals. It involves a runaway trolley, five helpless people on the track, and a large-framed man looking on from a footbridge. He may or may not be about to tumble to his bloody demise: You get to make the call.

That's because in this scenario, you are standing on the footbridge, too. You know that if you push the large man off the bridge onto the tracks, his body will stop the trolley before it kills the five people on the tracks. Of course, he will die in the process. So the question is: Is it morally permissible to kill the man in order to save five others?

In surveys, most people (around 85 percent) say they would not push the man to his death.

Often, this scenario is paired with a similar one: Again, there are five helpless people on the track. But this time, you can pull a switch that will send the runaway trolley onto a side track, where only one person is standing. So again, you can reduce the number of deaths from five to one-but in this case most people say, yes, they would go ahead and pull the lever. Why do we react so differently to the two scenarios?

Moral philosophers, if not the man on the street, can offer a few subtle logical distinctions between the cases. In the first, the fat man is being used essentially as a tool, or instrument, toward another goal. That violates the Kantian principle that human beings are ``ends" in themselves and should never be treated as mere instruments. Also, in the second scenario, the death of the innocent man can be viewed as a lamentable side effect of the chief goal, which is getting the train off the main track. This explanation is sometimes called the doctrine of the double effect: You'd pull that switch whether or not someone was on the track.

In a well-known paper that appeared in Science in 2001, however, Joshua D. Greene, then a post-doc in the Princeton psychology department, and four coauthors proposed that, whatever the philosophers said, for ordinary people the main issue was simply that pushing someone to his death-touching him and perhaps looking into his eyes-ignited an intense emotional response, whereas flipping a switch did not.

Greene, now an assistant professor at Harvard, administered MRI scans to subjects who were weighing both scenarios. While both groups showed increased activity in areas of the brain associated with intense reasoning, only in the case of those considering the footbridge scenario did the regions of the brain associated with emotion ``light up."

Greene and his colleagues described the finding as a partial victory for David Hume, the British philosopher who wrote that reason was a ``slave to the emotions." But more precisely, they described moral decision-making as a process in which reason and emotion duke it out within the mind. The finding, they added, was also a blow to older theories of human development, which held that as we become adults, we stop making moral decisions with our emotions, as children do.

In the June issue of Psychological Science, Piercarlo Valdesolo, a Northeastern University graduate student in psychology, and David DeSteno, a Northeastern professor, tightened the link between our emotions and our morals. They asked 79 subjects to consider the two trolley scenarios. But first, they had about half the subjects view a five-minute clip of ``Saturday Night Live" to put them in a good mood. The others watched a clip of a dry documentary on a Spanish village.

Valdesolo and DeSteno found that the SNL-watchers were more likely to say they would push the large man off the bridge. What seemed to be happening, they wrote, was that the happy mood caused by the video clip partly offset the negative emotions caused by the idea of directly killing a man. ``By changing the emotional response," says DeSteno, ``I can change your moral judgments."

Philosophers often caution that how we act in real life, never mind the laboratory, shouldn't determine how we ought to act. But Greene, Valdesolo, and DeSteno point out that, at the least, the results should lead us to be skeptical about our snap moral decisions, however natural and obvious they seem, as they may be very much affected by the mood we happen to be in.