Would You Kill the Big Guy?

This is the story of an obese gentleman, runaway trains, killing and saving lives. The series examines moral philosophy and our deepest moral intuitions through a single famous thought-experiment. Would you kill the big guy?

Here's the scenario; a train is hurtling down a railway line, it's out of control and the brakes have failed. Ahead, five people are tied to the track - all five apparently face certain death.

You however, are standing by the rails, and have a chance to save them. By turning a signal switch you can divert the train down another track. The only problem is that one person is bound to this other track. What should you do? Should you flick the switch?

Now you've answered that, try this. The runaway train is again heading towards five people. This time you're standing on a footbridge, next to a very big man. The only way you can stop the train is to push the big man over the footbridge onto the track. His bulk will stop the train and five lives will be spared. What should you do? Should you push him?

Most people answer 'yes' to the first puzzle and 'no' to the second. But why might the two train cases be morally different? What does the conundrum tell us about what sort of moral creatures human beings are? And why does any of this matter?

It's a moral conundrum that philosophers have been grappling with for several decades. It may seem like just a fun poser, a crossword puzzle for philosophers - but in fact the answers we give in such cases have huge implications in numerous practical areas, such as abortion, capital punishment and the conduct of warfare.

There are now so many trolley (an alternative word for a train or tram) puzzles that they've even been given a name, trolley-ology.

Steve Evans explores the tram puzzles, to see what it tells us about what kind of moral creatures humans are.

First broadcast on 12 May 2010