You are standing at a fork in a trolley track, your hand on the lever that can cause the trolley to go one direction or the other. A trolley is coming toward you. If you do not pull the lever, it will go down the fork where five children are on the track. They will surely be killed. (They are tied up, or facing the wrong direction and deaf, or what have you.) If you do pull the lever, their lives will be saved, but your own child, who is immobile on the other fork, will be killed. What is the ethical thing to do?
This is possibly the earliest in a famous series of ethical dilemmas known as trolley problems.
The fun begins when we vary the scenario to tease out people’s moral intuitions. Philosopher Judith Jarvis Thompson posed the most famous version:
As before, a trolley is hurtling down a track towards five people. You are on a bridge under which it will pass, and you can stop it by putting something very heavy in front of it. As it happens, there is a very fat man next to you – your only way to stop the trolley is to push him over the bridge and onto the track, killing him to save five. Should you proceed? [quoted in Wikipedia]
Path of the Beagle 