Philosophy Question: Would You Kill One Person to Save Five?

The “Trolley Problem”

Passengers Riding a Trolley. Getty Images

Philosophers love to conduct thought experiments.  Often these involve rather bizarre situations, and critics wonder how relevant these thought experiments are to the real world.  But the point of the experiments is to help us clarify our thinking by pushing it to the limits.  The “trolley dilemma” is one of the most famous of these philosophical imaginings.

The Basic Trolley Problem

A version of this  moral dilemma was first put forward in 1967 by the British moral philosopher Phillipa Foot, well-known as one of those responsible for reviving virtue ethics.

  Here’s the basic dilemma.  A tram is running down a track and is out control.  If it continues on its course unchecked and undiverted, it will run over five people who have been tied to the tracks.  You have the chance to divert it onto another track simply by pulling a lever.  If you do this, though, the tram will kill a man who happens to be standing on this other track. What should you do?

The Utilitarian Response

For many utilitarians the problem is a no-brainer.  Our duty is to promote the greatest happiness of the greatest number.  Five lives saved is better than one life saved.  Therefore, the right thing to do is to pull the lever.

Utilitarianism is a form of consequentialism.  It judges actions by their consequences.  But there are many who think that we have to consider other aspects of action as well.  In the case of the trolley dilemma, many are troubled by the fact that if they pull the lever they will be actively engaged in causing the death of an innocent person.

  According to our normal moral intuitions, this is wrong, and we should pay some heed to our normal moral intuitions.

So-called “rule utilitarians” may well agree with this point of view.  They hold that we should not judge every action by its consequences.  Instead, we should establish a set of moral rules to follow according to which rules will promote the greatest happiness of the greatest number in the long term.

  And then we should follow those rules, even if in specific cases doing so may not produce the best consequences.

But so-called “act utilitarians” judge each act by its consequences; so they will simply do the math and pull the lever.  Moreover, they will argue that there is no significant difference between causing a death by pulling the lever and not preventing a death by refusing to pull the lever.  One is equally responsible for the consequences in either case. 

Those who think that it would be right to divert the tram often appeal to what philosophers call the doctrine of double effect.  Simply put, this doctrine states that it is morally acceptable to do something that causes a serious harm in the course of promoting some greater good  if the harm in question is not an intended consequence of the action but is, rather, an unintended side-effect.  The fact that the harm caused is predictable doesn’t matter.  What matters is whether or not the agent intends it. 

The doctrine of double effect plays an important role in just war theory. It has often been used to justify certain military actions which cause “collateral damage.”  An example of such an action would be the bombing of an ammunition dump that not only destroys the military target but also causes a number of civilian deaths.


Studies show that the majority of people today, at least in modern Western societies, say that they would pull the lever.  However, they respond differently when the situation is tweaked.

Variations on the Basic Trolley Dilemma


The Fat Man on the Bridge

The situation is the same as before: a runaway tram threatens to kill five people.  A very heavy man is sitting on a wall on a bridge spanning the track.  You can stop the train by pushing him off the bridge onto the track in front of the train.  He will die, but the five will be saved.  (You can’t opt to jump in front of the tram yourself since you aren’t big enough to stop it.)

From a simple utilitarian point of view, the dilemma is the same–do you sacrifice one life to save five?–and the answer is the same: yes.  Interestingly, however, many people who would pull the lever in the first scenario would not push the man in this second scenario.

This raises two questions.

The Moral Question: If Pulling the Lever Is Right, Why Would Pushing the Man Be Wrong?

One argument for treating the cases differently is to say that the doctrine of double effect no longer applies if one pushes the man off the bridge.  His death is no longer an unfortunate side-effect of your decision to divert the tram; his death is the very means by which the tram is stopped.  So you can hardly say in this case that when you pushed him off the bridge you weren’t intending to cause his death.

A closely related argument is based on a moral principle mad famous by the great German philosopher Immanuel Kant (1724-1804).  According to Kant we should always treat people as ends in themselves, never merely as a means to our own ends.  This is commonly known, reasonably enough, as the “ends principle.”  It is fairly obvious that if you push the man off the bridge to stop the tram, you are using him purely as a means.  To treat him as end would be to respect the fact that he is a free, rational being, to explain the situation to him, and suggest that he sacrifice himself to save the lives of those tied to the track.  Of course, there is no guarantee that he would be persuaded.  And before the discussion had got very far the tram would have probably already passed under the bridge!

The Psychological Question: Why Will People Pull the Lever but Not Push the Man?

Psychologists are concerned not with establishing what is right or wrong but with understanding why people are so much more reluctant to push a man to his death than to cause his death by pulling a lever.  The Yale psychologist Paul Bloom suggests that the reason lies in the fact that our causing the man’s death by actually touching him arouses in us a much stronger emotional response.  In every culture there is some sort of taboo against murder.  An unwillingness to kill an innocent person with our own hands is deeply ingrained in most people. This conclusion seems to be supported by people’s response to another variation on the basic dilemma.

The Fat Man Standing on the Trapdoor

Here the situation is the same as before, but instead of sitting on a wall the fat man is standing on a trapdoor built into the bridge.  Once again you can now stop the train and save five lives by simply pulling a lever. But in this case pulling the lever will not divert the train.  Instead, it ill open the trapdoor, causing the man to fall through it and onto the track in front of the train.

Generally speaking, people are not as ready to pull this lever as they are to pull the lever that diverts the train.  But significantly more people are willing to stop the train in this way than are prepared to push the man off the bridge. 

The Fat Villain on the Bridge

Suppose now that the man on the bridge is the very same man who has tied the five innocent people to the track.  Would you be willing to push  this person to his death to save the five?  A majority say they would, and this course of action seems fairly easy to justify.  Given that he is willfully trying to cause innocent people to die, his own death strikes many people as thoroughly deserved.  The situation ios more complicated , though, if the man is simply someone who has done other bad actions.  Suppose in the past he has committed murder or rape and that he hasn’t paid any penalty for these crimes.  Does that justify violating Kant’s ends principle and using him as a mere means? 

The Close Relative on the Track

Here is one last variation to consider.   Go back to the original scenario–you can pull a lever to divert the train so that five lives are saved and one person is killed–but this time the one person who will be killed is your mother, or your brother.  What would you do in this case?  And what would be the right thing to do?

A strict utilitarian may have to bite the bullet here and be willing to cause the death of their nearest and dearest.  After all, one of the basic principles of utilitarianism is that everyone’s happiness counts equally.  As Jeremy Bentham, one of the founders of modern utilitarianism, put it: Everyone counts for one; no-one for more than one.  So sorry mom! 

But this is most definitely not what most people would do.  The majority may lament the deaths of the five innocents, but they cannot bring themselves to bring about the death of a loved one in order to save the lives of strangers.  That is most understandable from a psychological point of view.  Humans are primed both in the course of evolution and through their upbringing to care most for those around them.  But is it morally legitimate to show a preference for one’s own family?

This is where many people feel that strict utilitarianism is unreasonable and unrealistic.  Not only will we tend to naturally favor our own family over strangers, but many think that we ought to.  For loyalty is a virtue; and loyalty to one’s family is about as basic a form of loyalty as there is. So in many people’s eyes, to sacrifice family for strangers goes against both our natural instincts and our most fundamental moral intuitions.