The Fat Man
A runaway trolley will kill five people. The only way to stop it is to push a large man off a bridge onto the tracks. His body will stop the trolley, but he will die. Do you push him?
This variation on the trolley problem, introduced by philosopher Judith Jarvis Thomson in 1985, is designed to distinguish between different moral intuitions. Most people who would pull the lever in the original trolley problem refuse to push the man, even though the arithmetic is identical. The question is: why?
The numbers are the same
In the original trolley problem, you pull a lever: one dies, five live. Most people say pull.
In this version, you push a person to their death: one dies, five live. Most people say don't push.
The outcomes are mathematically equivalent. The moral intuitions are different. If you're a pure utilitarian, this inconsistency needs explaining.
What changes between the cases
Several theories try to explain the difference:
- The use/harm distinction: in the lever case, the one death is a side effect of redirecting the trolley. In the bridge case, the man's body is the means by which you save the five. His death is instrumental to your purpose, not incidental.
- Personal force: pushing someone to their death involves physical contact, which triggers a visceral moral response even when the calculations are the same.
- Rights-based reasoning: you may not use a person's body as a tool to benefit others, even with their welfare in mind.
What the inconsistency reveals
Thomson used this case to argue against pure consequentialism. The fact that almost everyone has a strong intuition not to push suggests that something other than outcomes is doing moral work: agent-relative constraints, rights, or the distinction between doing and allowing harm.
Neuroscientists have since confirmed that the two scenarios activate different brain regions: the bridge case triggers the emotional brain more strongly, which may explain why the reasoning brain loses.
The challenge
If you wouldn't push, would you ask someone else to push? Would you push a button that pushed him? At what distance does your reluctance fade, and does that distance tell you something true about morality or something true about your psychology?