Would You Kill One to Save Five?
Do you pull the lever to divert the trolley?
A runaway trolley is heading toward five people tied to the tracks. You stand next to a lever that can divert the trolley onto a side track—where only one person is tied. If you pull the lever, you save five but kill one. If you do nothing, five die.
| Scenario | Would Kill the One | Would Let Five Die |
|---|---|---|
| The Switch | ~90% | ~10% |
| The Footbridge | ~10% | ~90% |
| The Loop | ~50% | ~50% |
"Why is it that most people say you should flip the switch in the first case, but not push the fat man in the second? The result is the same: one dead, five saved."— The central puzzle of the Trolley Problem
It may be permissible to cause harm as a side effect of achieving a good, but not to cause harm as a means to a good. In the Switch, death is a side effect; in the Footbridge, it's the means.
Is there a moral difference between actively causing harm and merely allowing it to happen? Pulling the lever feels like redirecting; pushing feels like killing.
fMRI studies show different brain regions activate. Pushing someone with your hands triggers emotional responses that pulling a lever doesn't.
In the Footbridge, you use the person's body as a trolley-stopper. In the Switch, the person isn't "used"—they're just unfortunately on the track.
From a pure numbers perspective, the answer is always the same: five lives > one life. The method shouldn't matter if the outcome is identical.
Self-driving cars face trolley problems constantly. How should they be programmed? These thought experiments have real engineering implications.