What are the three famous moral problems used to test how far a "greater good" can justify an act?
Would you kill, torture, or lie for a greater good? — the trolley footbridge case, the ticking-bomb torture case, and the murderer at the door.
Each strips away everything except the one question, and each targets a different absolute prohibition:
- The trolley problem — would you kill for a higher good? A runaway train will kill five people on the tracks, unless a heavy man is pushed onto the rails, stopping the train but killing him.
- The torture problem — would you torture for a higher good? If person A does not violate the duty not to torture person B, ten million innocent people will die in a nuclear strike.
- The lying problem — would you lie for a higher good? A murderer pursues his victim, who hides in a house. Searching for him, the murderer asks a resident — who saw the victim go in — whether he ran into the house. The dilemma: a general prohibition on lying cannot hold in such a situation; and yet the murderer, too, has a right not to be lied to.
The cases are deliberately artificial, and that is their point rather than a flaw: by guaranteeing the outcome and removing every escape route, they force you to say whether the prohibition is absolute or merely very weighty. Most people answer differently across the three — willing to lie, unwilling to torture — which is itself the interesting datum, since a consistent consequentialist should treat all three alike and a consistent deontologist should refuse all three.
The third case is the famous one because Kant himself bit the bullet and said one must not lie even to the murderer — a conclusion many of his own followers have spent two centuries trying to avoid.
Go deeper:
Michael Sandel — Justice, Episode 1: »The Moral Side of Murder« — the Harvard lecture that runs a hall of students straight into these cases and makes them defend their answers.
Wikipedia: Ticking time bomb scenario — the torture case and the strong argument that its artificiality is doing the persuading.- Kant: On a Supposed Right to Tell Lies from Benevolent Motives — the essay where Kant bites the bullet on the murderer at the door.