Sunday, 21 June 2009

The Trolley dilemma revisited

Most of us agree that murder, rape and plunder are wrong. Moral psychology gets more tricky when the interests of the many are pitted against the few, as in the classic "trolley dilemma", in which a person must divert a hurtling trolley towards a lone victim, so as to save the lives of five others. In a new analysis, using multiple variants of this classic moral brain-teaser, Joshua Greene and colleagues show that when it comes to judging the moral acceptability of a person's actions, there seems to be something special about whether or not they used their own muscular force, and whether or not they intended any subsequent harm caused.

In an initial experiment, over 600 students judged the moral acceptability of four versions of the trolley dilemma. In the first, "Joe" must save the five by pushing a victim into the trolley's path. The second involves Joe dropping the victim through a trap-door into the trolley's path, using a switch in a remote location. The third was identical the second, but the switch is adjacent to the victim. The final fourth variation involves Joe pushing the victim into the trolley's path with a pole.

Spatial proximity appeared to be an irrelevant factor - the location of the trap-door switch made no difference to the students' moral judgements. Actual physical contact, too, seemed to be irrelevant - Joe pushing the victim with a pole was judged as immoral as with his hands. Crucially, however, using one's own bodily strength made an action less morally acceptable, as evinced by Joe's pole pushing being rated as morally worse than his use of the trap-door switch.

A second experiment developed this idea and showed further that an action is most morally condemnable when personal force and intention co-occur. Students judged as most morally unacceptable a situation in which Joe deliberately pushed a victim off a bridge so that he could reach a switch to save five others. By contrast, if the victim was knocked off the bridge accidentally so Joe could reach the switch, or if Joe killed him by diverting a trolley with a switch, then the students' moral judgements were not so harsh.

"Put simply, something special happens when intention and personal force co-occur," the researchers said. This prompts many further questions, such as what counts as personal force. "Must it be continuous (as in pushing), or may it be ballistic (as in throwing)?" the researchers asked. "Is pulling the same as pushing?"

ResearchBlogging.orgGreene, J., Cushman, F., Stewart, L., Lowenberg, K., Nystrom, L., & Cohen, J. (2009). Pushing moral buttons: The interaction between personal force and intention in moral judgment. Cognition, 111 (3), 364-371 DOI: 10.1016/j.cognition.2009.02.001

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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