The trolley problem is a thought experiment in ethics that presents a scenario where a runaway trolley is barreling down railway tracks towards five people. You are standing next to a lever that can divert the trolley onto a side track, but there is one person on that track who will be killed if you pull the lever. There are two options: do nothing and the five people die, or pull the lever and the one person dies. Related problems modify this scenario, such as adding a "fat man" who could be pushed in front of the trolley to stop it. The trolley problem explores moral dilemmas around consequentialism, utilitarianism, and directly harming others.

1. Trolley problem
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The trolley problem is a thought experiment in ethics, first introduced by Philippa Foot in 1967,[1] but also
extensively analysed by Judith Jarvis Thomson,[2][3] Peter Unger,[4] and Frances Kamm as recently as
1996.[5] Outside of the domain of traditional philosophical discussion, the trolley problem has been a significant
feature in the fields of cognitive science and, more recently, of neuroethics. It has also been a topic on various
TV shows dealing with human psychology.[citation needed]
The general form of the problem is this: There is a runaway trolley barrelling down the railway tracks. Ahead,
on the tracks, there are five people tied up and unable to move. The trolley is headed straight for them. You are
standing some distance off in the train yard, next to a lever. If you pull this lever, the trolley will switch to a
different set of tracks. Unfortunately, you notice that there is one person on the side track. You have two
options: (1) Do nothing, and the trolley kills the five people on the main track. (2) Pull the lever, diverting the
trolley onto the side track where it will kill one person. Which is the correct choice?
Contents
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 1 Overview
 2 Related problems
o 2.1 The fat man
o 2.2 The fat villain
o 2.3 The loop variant
o 2.4 Transplant
o 2.5 The man in the yard
 3 In cognitive science
 4 In neuroethics
 5 Psychology
 6 Views of professional philosophers
 7 As urban legend
 8 See also
 9 References
 10 External links

2. Overview[edit]
Foot's original formulation of the problem ran as follows: [1]
Suppose that a judge or magistrate is faced with rioters demanding that a culprit be found for a certain
crime and threatening otherwise to take their own bloody revenge on a particular section of the
community. The real culprit being unknown, the judge sees himself as able to prevent the bloodshed
only by framing some innocent person and having him executed. Beside this example is placed
another in which a pilot whose aeroplane is about to crash is deciding whether to steer from a more to
a less inhabited area. To make the parallel as close as possible it may rather be supposed that he is
the driver of a runaway tram which he can only steer from one narrow track on to another; five men are
working on one track and one man on the other; anyone on the track he enters is bound to be killed. In
the case of the riots the mob have five hostages, so that in both the exchange is supposed to be one
man's life for the lives of five.
A utilitarian view asserts that it is obligatory to steer to the track with one man on it. According to simple
utilitarianism, such a decision would be not only permissible, but, morally speaking, the better option (the
other option being no action at all).[6] An alternate viewpoint is that since moral wrongs are already in place
in the situation, moving to another track constitutes a participation in the moral wrong, making one partial ly
responsible for the death when otherwise no one would be responsible. An opponent of action may also
point to the incommensurability of human lives. Under some interpretations of moral obligation, simply
being present in this situation and being able to influence its outcome constitutes an obligation to
participate. If this were the case, then deciding to do nothing would be considered an immoral act if one
values five lives more than one.
Related problems[edit]
The initial trolley problem becomes more interesting when it is compared to other moral dilemmas.
The fat man[edit]
One such is that offered by Judith Jarvis Thomson:
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 dropping a heavy weight 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?
Resistance to this course of action seems strong; most people who approved of sacrificing one to
save five in the first case do not approve in the second sort of case.[7] This has led to attempts to find
a relevant moral distinction between the two cases.

3. One clear distinction is that in the first case, one does not intend harm towards anyone – harming the
one is just a side effect of switching the trolley away from the five. However, in the second case,
harming the one is an integral part of the plan to save the five. This is an argument Shelly
Kagan considers, and ultimately rejects, in The Limits of Morality.[8]
A claim can be made that the difference between the two cases is that in the second, you intend
someone's death to save the five, and this is wrong, whereas in the first, you have no such intention.
This solution is essentially an application of the doctrine of double effect, which says that you may
take action which has bad side effects, but deliberately intending harm (even for good causes) is
wrong.
Act utilitarians deny this. So do some non-utilitarians such as Peter Unger, who rejects that it can
make a substantive moral difference whether you bring the harm to the one or whether you move the
one into the path of the harm.[citation needed] Note, however, that rule utilitarians do not have to accept
this, and can say that pushing the fat man over the bridge violates a rule to which adherence is
necessary for bringing about the greatest happiness for the greatest number. [citation needed]
Another distinction is that the first case is similar to a pilot in an airplane that has lost power and is
about to crash and currently heading towards a heavily populated area. Even if he knows for sure that
innocent people will die if he redirects the plane to a less populated area – people who are
"uninvolved" – he will actively turn the plane without hesitation. It may well be considered noble to
sacrifice your own life to protect others, but morally or legally allowing murder of an innocent person in
order to save five people may be insufficient justification.[clarification needed]
The fat villain[edit]
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The further development of this example involves the case, where the fat man is, in fact, the villain
who put these five people in peril. In this instance, pushing the villain to his death, especially to save
five innocent people, seems not just moral, but, to some, [who?] also just and even an imperative. This is
essentially related to another famous thought experiment, known as ticking time bomb scenario, which
forces one to choose between two morally questionable acts. Several papers argue that ticking time
bomb scenario is a mere variation of the trolley problem.
The loop variant[edit]

4. The claim that it is wrong to use the death of one to save five, runs into a problem with variants like
this:
As before, a trolley is hurtling down a track towards five people. As in the first case, you can divert it
onto a separate track. However, this diversion loops back around to rejoin the main track, so diverting
the trolley still leaves it on a path to run over the five people. But, on this track is a single fat person
who, when he is killed by the trolley, will stop it from continuing on to the five people. Should you flip
the switch?
The only difference between this case and the original trolley problem is that an extra piece of
track has been added, which seems a trivial difference (especially since the trolley won't travel
down it anyway). So, if we originally decided that it is permissible or necessary to flip the switch,
intuition may suggest that the answer should not have changed. However, in this case, the death
of the one actually is part of the plan to save the five.
The rejoining variant may not be fatal to the "using a person as a means" argument. This has
been suggested by M. Costa in his 1987 article "Another Trip on the Trolley", where he points out
that if we fail to act in this scenario we will effectively be allowing the five to become a means to
save the one. If we do nothing, then the impact of the trolley into the five will slow it down and
prevent it from circling around and killing the one.[citation needed] As in either case, some will become
a means to saving others, then we are permitted to count the numbers. This approach requires
that we downplay the moral difference between doing and allowing.
However, this line of reasoning is no longer applicable if a slight change is made to the track
arrangements such that the one person was never in danger to begin with, even if the 5 people
were absent. Or even with no track changes, if the one person is high on the gradient while the
five are low, such that the trolley cannot reach the one. So the question has not been answered.
Even in the situation where the people aren't tied down due to a criminal act, but simply happen
to be there without the ability to warn them, the out-of-control trolley is similar to the out-of-control
airplane. Either 5/500 or 1/100 people are going to die as a result of the accident already in
progress, and it is important to minimize the loss of life, despite the fact that the 1/100 are
effectively being "used" to spare the life of the 5/500. The 100 people (and their property) in the
less-densely-populated area do in fact stop the plane too. Responsibility for this goes back to any
criminal negligence that caused the accident to occur in the first place.
Transplant[edit]
Here is an alternative case, due to Judith Jarvis Thomson, [3] containing similar numbers and
results, but without a trolley:

5. A brilliant transplant surgeon has five patients, each in need of a different organ, each of whom will die
without that organ. Unfortunately, there are no organs available to perform any of these five transplant
operations. A healthy young traveler, just passing through the city the doctor works in, comes in for a
routine checkup. In the course of doing the checkup, the doctor discovers that his organs are
compatible with all five of his dying patients. Suppose further that if the young man were to disappear,
no one would suspect the doctor.
The man in the yard[edit]
Unger argues extensively against traditional non-utilitarian responses to trolley problems.
This is one of his examples:
As before, a trolley is hurtling down a track towards five people. You can divert its path by colliding
another trolley into it, but if you do, both will be derailed and go down a hill, and into a yard where a
man is sleeping in a hammock. He would be killed. Should you proceed?
Responses to this are partly dependent on whether the reader has already encountered
the standard trolley problem (since there is a desire to keep one's responses
consistent), but Unger notes that people who have not encountered such problems
before are quite likely to say that, in this case, the proposed action would be wrong.
Unger therefore argues that different responses to these sorts of problems are based
more on psychology than ethics – in this new case, he says, the only important
difference is that the man in the yard does not seem particularly "involved". Unger
claims that people therefore believe the man is not "fair game", but says that this lack of
involvement in the scenario cannot make a moral difference.
Unger also considers cases which are more complex than the original trolley problem,
involving more than just two results. In one such case, it is possible to do something
which will (a) save the five and kill four (passengers of one or more trolleys and/or the
hammock-sleeper), (b) save the five and kill three, (c) save the five and kill two, (d) save
the five and kill one, or (e) do nothing and let five die. Most naïve subjects presented
with this sort of case, claims Unger, will choose (d), to save the five by killing one, even
if this course of action involves doing something very similar to killing the fat man, as in
Thomson's case above.[citation needed]
This scenario is similar to the fact that whenever a crime is in progress and someone
calls the police, even though it is known well in advance that calls to police each year
end up creating pedestrian and motorist deaths due to accidents, very few people would
consider disbanding the police to ensure that no innocents should die en route to a

6. crime scene. In the case where the five aren't tied down due to a criminal act, it still falls
into the category of diverting a crashing plane into a less-densely-populated area.
In cognitive science[edit]
The trolley problem was first imported into cognitive science from philosophy in a
systematic way by Hauser, Mikhail, et al,[9] They hypothesized that factors such as
gender, age, education level, and cultural background would have little influence on the
judgments people make, in part because those judgments are generated by an
unconscious “moral grammar”[10] that is analogous in some respects to the unconscious
linguistic grammars that have been claimed byNoam Chomsky et al to support ordinary
language use ( this latter claim regarding language has been strongly rebutted by Dan
Everett and by Evans and Levinson.[11]) It should be noted that the data in Hauser,
Mikhail et al's 2007 paper only contains 33 individuals brought up in a non-English-speaking
educational system. The main author, Marc Hauser, was subsequently
sanctioned by his then employer, Harvard University, in eight (unrelated) cases of gross
research malpractice and data falsification, which arguably makes the data in any case
unreliable. Subsequent cross-cultural research has found many apparent
counterexamples to this idea of 'Universal Moral Grammar'[12]
In neuroethics[edit]
In taking a neuroscientific approach to the trolley problem, Joshua Greene[13] under
Jonathan Cohen decided to examine the nature of brain response to moral and ethical
conundra through the use of fMRI. In their more well-known experiments,[14] Greene and
Cohen analyzed subjects' responses to the morality of responses in both the trolley
problem involving a switch, and a footbridge scenario analogous to the fat man variation
of the trolley problem. Their hypothesis suggested that encountering such conflicts
evokes both a strong emotional response as well as a reasoned cognitive response that
tend to oppose one another. From the fMRI results, they have found that situations
highly evoking a more prominent emotional response such as the fat man variant would
result in significantly higher brain activity in brain regions associated with response
conflict. Meanwhile, more conflict-neutral scenarios, such as the relatively disaffected
switch variant, would produce more activity in brain regions associated with higher
cognitive functions. The potential ethical ideas being broached, then, revolve around the
human capacity for rational justification of moral decision making.
Psychology[edit]

7. In many years of surveys, the vast majority of people — usually about 90% — have
chosen to kill the one and save the five. But until now, there’s never been a study
examining how people would react in a lifelike setting with real-looking potential victims.
In the Michigan State study, led by psychologist David Navarette, the 147 participants
made their choice while wearing a head-mounted virtual-reality device that projected
avatars of those who could die. One chilling factor of the test: the potential victims were
screaming as the boxcar approached.
The 147 subjects also had electrodes attached to their skin in order to measure their
autonomic responses, the involuntary nervous-system responses that can spike when
we are faced with stress. Navarette and his team found that, once again, 90% of us
would kill the one to save the five. Among the 147 participants, 133 pulled the switch.
Interestingly, those who were more emotionally aroused during the simulation — based
on measurements of electrical conductivity along the skin — were less likely to kill the
one.
In another test, the Michigan State team changed the experiment so that the train would
kill the one person unless it was diverted to kill the five. In other words, this time the
participants had to choose passive, restrained action: just let the train continue on its
course and run over the single person. Once again, 90% chose to save the five over the
one. This group was also, on average, less emotionally excited than the 10% who had to
act to save the one life.
[15