Assuming all these facts, I expect you to agree with me that it would be morally permissible for Homer to pull the trigger. It seems an ordinary case of self-defense albeit against an unusual attack.

SELF DEFENSE A runaway trolley is coming down the track. Luckily there is no one in its path. A passerby, Burns, sees this but he also notices that Homer, someone he hates, is standing on a siding. Burns realizes that if he throws a nearby switch, the trolley will be diverted down the siding killing Homer. Homer can see all this too and when he sees Burns moving towards the switch he correctly guesses his intent. Homer cannot get out of the way but he is not defenseless: he has a gun. He draws it and shouts "Stop or I'll shoot!". But Burns ignores him and keeps moving the switch.

Now there is a line of thought that says that when one's life is in danger, anything goes. The philosopher Hobbes seems to have held something like this position. But this seems to me to throw morality out the window when it may be most required. It seems to me that SHIELDING ONESELF and SACRIFICING OTHERS are clearly impermissible and in what follows I'm going to assume you agree with me.

SHIELDING ONESELF A man sees that someone is about to shoot him. To protect himself, he grabs an innocent bystander and uses her as a shield.

Is it morally permissible for the man to throw the switch? If it is permissible, what of this:

SACRIFICING OTHERS A runaway trolley is coming down the track. It is headed towards a Lone Man on the tracks who cannot get out of the way. However that man is standing by a switch which, if thrown, will divert the trolley down a siding. In that case the man will be safe but he can also see that, in that case, five people standing on the siding will be killed.

In a conflict between folk intuitions and philosophical theory I'll bet on the folk every time. In this post, I'm not going to take a position on whether or not it is permissible to turn in TROLLEY or push the FAT MAN. My goal instead is to show that, as described, there are subtle but important differences between the FAT MAN and TROLLEY cases; differences that can make a moral difference in other circumstances, but differences that have, hitherto, gone overlooked by philosophers.

Both sides explain away "folk intuitions" that the cases are somehow different as a psychological aberration. Folks feel better about killing other folks in TROLLEY-- this theory goes-- because they are more comfortable with throwing a remote switch in TROLLEY than they are with the up close shoving that FAT MAN requires. There are even psychological " experiments " and ( God help us ) neural imaging studies that are supposed to explain (away) these folksy confusions.

Meanwhile Judith Jarvis Thomson concludes that, since there is no difference between the cases, it must be wrong to turn in TROLLEY and so FAT MAN represents a reductio ad absurdum of Utilitarianism.

Thus a Utilitarian like Peter Unger can argue that, since there is no difference, it must be morally okay to go around doing things like pushing fat men under trolleys so long as it promotes the general happiness.

In the almost forty years since Judith Jarvis Thomson first posed the problem in this form there have many attempts to solve it but none is generally accepted as successful. Indeed a general consensus seems to have developed that the "folk intuitions" (as philosophers call them) about the difference between these cases are simply irrational.

Most people, including those who think it is okay to turn in TROLLEY, think that it is not okay to push the FAT MAN. "The Trolley Problem" is how to reconcile these two answers. In both cases it seems you can do something that will save five people but only by killing one. How can anyone think it okay to turn in TROLLEY but wrong to push the FAT MAN? What difference is there between the two stories that can possibly make a moral difference?

FAT MAN A runaway trolley is coming down the track. It is headed towards five people who cannot get out of its way. A passerby realizes that if he pushes a nearby fat man onto the tracks his bulk will stop the trolley before it hits the five, though the fat man himself will be killed.

Should you divert the trolley? Lots of folks say, "Yes!" Whether or not they are right is an interesting problem but it is not what philosophers call " The Trolley Problem ". That problem involves a different case:

TROLLEY A runaway trolley is coming down the track. It is headed towards five people who cannot get out of its way. A Passerby realizes that he can save the five by throwing a switch and diverting the trolley down a siding, but he also realizes that if he does so, the trolley will kill a Lone Man standing on the siding.

SELF DEFENSE WITH COLATERAL DAMAGE

A runaway trolley is coming down the track. It is headed towards five people who cannot get out of its way. A passerby, Burns, sees this and realizes that he can save the five by throwing a switch and diverting the trolley down a siding. Burns also realizes that if he does so the trolley will kill Homer, whom Burns hates. Homer can see all this too and when he sees Burns moving towards the switch he correctly guesses his intent. Homer cannot get out of the way but he is not defenseless. He has a gun…

The only external difference between this case and SELF DEFENSE is the presence of the people on the track but I have also subtracted any reference to Burns' motive. Feel free to imagine that Burns is primarily motivated by a desire to save the five, or primarily by a desire to kill Homer, or by the combination of the two, but be prepared to say why that makes a difference to the central question.

The central question being: is it permissible for Homer to use his gun to stop Burns?

I do not think that it is. Burns is going to divert the trolley and prevent the death of five people. If Homer or anyone else stops Burns, they will be causing the death of five people and preventing the death of only one. Of course, Homer's life is at risk, but we agreed when we considered the SACRIFICING OTHERS case that it was not permissible for him to save his own life by doing something that would cause the death of people who were no threat to him. That seems to apply in this case too, indeed more so because now he will be harming Burns in addition to causing the death of the five. Though I think that Homer would still be responsible for the death of the five if Burns were stopped by Homer's yelling "Stop". Nor it doesn't seem to me relevant to the case what Burn's motives happen to be.

If that is correct then we have discovered something. People who say that it is wrong to turn in TROLLEY sometimes argue that this is so because killing the man on the siding infringes his rights. But we seem to have just discovered that the man on the siding does not, in this circumstance, have all the rights that people ordinarily have. He doesn't have a right to self-defense. He lacks that right—at least against Burns-- because in this circumstance he can defend himself only by sacrificing others. And if Homer lacks the right to self-defense here, so does the Lone Man in the original TROLLEY case. As described, he didn't have a gun, but it doesn't matter: even if he did, he would not have had the right to use it save himself.

Now what about the Fat Man?

THE FAT MAN DEFENDS HIMSELF

A runaway trolley is coming down the track. It is headed towards five people who cannot get out of its way. A passerby, Flanders, realizes that if he pushes a nearby a fat man onto the tracks his bulk will stop the trolley before it hits the five, though the Fat Man himself will be killed. Flanders decides to push the Fat Man. The Fat Man sees all this, but he is not inclined to sacrifice himself to save the five and when he sees Flanders moving to push him onto the track he draws his gun and threatens "Stop or I'll shoot!". Flanders keeps coming...





Is it morally permissible for the Fat Man to shoot? All the arguments that applied in the case of SELF-DEFENSE WITH COLLATERAL DAMAGE seem to apply here as well. Flanders is going to do something that will keep five people from being killed. If the Fat Man or anyone else stops him they will be causing the death of those five people and saving the life of only one. The Fat Man could claim he was acting in in self-defense, but isn't defending himself in this case as bad as it is in SACRIFICING OTHERS?

Maybe, but there are differences: they have to do with the different alternatives available to Homer and the Fat Man.

Let us pause to remember that when we are deciding whether any action is permissible it is always relevant to ask what alternative actions are available. We all agree that it is morally impermissible to kill. But in a case in which one's only alternative to killing one person is to kill many people, most of us think that it is morally permissible if not mandatory to kill the one rather than kill the many.

Now the TROLLEY case is interesting because the passerby's alternatives are not whether to kill one or five but whether or not it is permissible to kill one rather than allow five to die. Some people think that allowing people to die is just as bad as killing them. But this is a minority view. Most people think that harming people is morally worse than allowing them to come to harm; TROLLEY tests that opinion.

The difference between allowing harm and causing it is especially vivid when preventing harm to others involves incurring harm ourselves. When the Fat Man stares at the speeding trolley his choice is whether to allow five strangers to die or to prevent their death by sacrificing himself. No one (at least, none of us folks) thinks this kind of sacrifice is morally required of him and none of us thinks that his refraining is equivalent to his killing five people. If the Fat Man jumped on his own he would be a hero precisely because he would have been acting above and beyond the demands of morality.

But the situation is different in the case where THE FAT MAN DEFENDS HIMSELF. If the Fat Man allows himself to be pushed, he will be sacrificing himself to save five. But if he resists he will be causing their death by preventing their rescue. Notice that this is not the choice that Homer faces in SELF DEFENSE WITH COLLATERAL DAMAGE. Homer's choice was between causing the death of the five -- by preventing their rescue—or allowing the five to be rescued. In the latter case, if the five are rescued, it won't be Homer's doing, but in the former, if the five are saved it will be the Fat Man who saves them, even if involuntarily.

Killing people when one has the alternative of letting them live is, other things being equal, plain murder. But the Fat Man's choice of whether to defend himself is between killing people versus preventing their death, and we view cases like these as morally different.

The most famous example of a dilemma like our Fat Man's is Judith Jarvis Thomson's Violinist case.

THOMSON'S VIOLINIST

You are knocked unconscious and kidnapped. When you wake you find your circulatory system is plugged into the body of a sickly violinist. The police have apprehended the kidnappers. They were fans of the violinist who were trying to keep him alive. You are now free to go but you are told that if you unplug yourself, the violinist will die. Only if you remain hooked up to the violinist for many months does the violinist have any chance of survival.

In Thomson's story your choice is between unplugging-- and thus causing the death of the violinist,--or sacrificing months of your life to prevent the violinist from dying. Thomson thought that, while it would be admirable of you to play the Good Samaritan in such a case, you were not morally obliged to do so. It would be permissible for you to unplug.

While farfetched, Thomson's story was not frivolous. It was meant to be analogous to:

ABORTION

A woman is raped. She discovers that she is pregnant. Her choice is to have an abortion or to bring the fetus to term.

Set aside the usual arguments about whether or not a fetus is a person. The violinist is certainly a person, but if we think you are not obliged to stay plugged into him, why should we think the rape victim is obliged to play Good Samaritan to the "person" plugged into her?

People have conflicting intuitions about such cases, and intuitions can change when variables vary (e.g. how long must one remain plugged in?). But there is a regularity in everyone's responses which is captured by a principle that Kadri Vihvelin and I dubbed "The Deontological Equivalence Principle"

The Deontological Equivalence Principle

Causing a death when one's only alternative is to prevent it, is morally equivalent to allowing a death when one has the alternative of preventing it.

The Principle does not take sides on whether you may or may not unplug. Instead it predicts that you will think it impermissible to unplug yourself from the violinist only if you think that you would have been obliged to plug yourself in, if you had been asked ahead of time. Alternatively, if you think morality does not require you to sacrifice yourself to save others, then you will think that morality permits you to cause their death when your only alternative is to sacrifice yourself to save them. Or again, if you think it is very, very bad, but not murder, to refuse to make a small sacrifice to save a life then you will think it just as bad, but not worse, to cause a death when, with the same sacrifice, you could prevent it.

If you think the Fat Man is morally obliged to throw himself onto the track to save the five, then you will think it equally wrong for him to prevent Flanders from pushing him. On the other hand if, like most of us, you think that the Fat Man is not required to throw himself in front of the trolley, you will agree that he is not obliged to let Flanders push him in front of it.

If that is right, then it is morally permissible for the Fat Man to defend himself against the push, just as it is permissible for him to refrain from jumping on his own. And that means the Fat Man does have the right to self-defense even though the Lone Man on the siding does not.

And we may note that the same arguments apply to all the cases to which Fat Man is sometimes compared. Thus:

FORCED TRANSPLANT

You learn that a doctor has plans to kidnap you and use your vital organs to save the lives of five other people. But you have a gun… UTILITARIAN JUDGE

You learn that a judge plans to hang you for a crime you did not commit in order to prevent riots in which many people will be killed. But you have a chance to escape…

In both these cases, your eluding the threat will lead to the death of innocent people, but we may think that permissible given that your only alternative is to sacrifice yourself to prevent those deaths.

What does all this show?

Well, there are some theories of self-defense that entail that a person has the right to self-defense if but only if it is impermissible to harm them. Perhaps that is the theory that underlies the intuition that it is permissible to turn in TROLLEY but not in FAT MAN.

Then too, according to many accounts of self-defense, the right self-defense entrains the right of "other-defense"; so that if someone is permitted to defend themselves against an action then others are likewise permitted to intervene to help them prevent it. Perhaps, when folks express qualms about pushing the Fat Man they are sensitive to the fact that it may be permissible for third parties to forcibly restrain them.

Or, maybe, folks see a moral difference between, on the one hand, saving the lives of five people and, on the other, forcing someone else to save those lives.

Perhaps, at the end of the day, we'll decide that folk's reasons, whatever they are, are not good. But to be entitled to that conclusion we'll have to work a lot harder at understanding the reasons folks say what they do.

Folks are smart; smarter than philosophers give them credit for. I recommend philosophers do fewer experiments, and use more imagination.