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Trolley dilemma: To be or not to be?

Trolley dilemma: To be or not to be?

Imagine this: You are standing right next to a lever in a train yard. If you pull down the lever, you can change the direction of the trolley to a different set of tracks. From your view, there are five hostages tied up on the main track and one innocent bystander on the side track, where escape is impossible for both parties. Right at this moment, there is a runaway trolley heading to the main track, and you are to decide whether you would do nothing and let the trolley kill the five men on the main track, or would you pull down the lever and sacrifice the bystander to save the group. We all may have our own answers now, whether to pull or not to pull the lever, but what exactly is the right thing to do?

Figure 1: Trolley dilemma A (photo credited to McGeddon, from Wikipedia)

① Ethical dilemma

Half a century ago, Foot (1967) introduced and named this scenario as trolley dilemma or trolley problem. It is a hypothetical thought experiment in ethics, in which the answers represent two important schools of moral thought, utilitarianism and deontology.

Mind map: What is utilitarianism and deontology?

In this context, utilitarianism seeks to save the most lives, whereas deontology follows the rule to not harm innocent people when they are not threatened. Throughout the years, researchers have developed different trolley dilemmas with a similar structure. However, it is very unlikely for people to always take an action (i.e., extreme utilitarianism) or not to take any action ever (i.e., extreme deontology).


Figure 2: Utilitarianism (disclaimer: this picture is used for illustration purpose only)
Figure 3: Deontology (disclaimer: this picture is used for illustration purpose only)
Figure 4: Utilitarianism vs. deontology (disclaimer: this picture is used for illustration purpose only)

Let us consider another similar example: Imagine that you are at a train station again, but this time you are standing on a higher platform. Again, the trolley is heading towards five men on the main track. You do not have the lever this time, but there is a man in front of you who is large enough to stop the trolley. Now, you are to decide whether you would do nothing and let the trolley kill the five men on the main track, or would you push the big men in front of you onto the tracks and sacrifice one to save the group. Again, what will you do?

Figure 5: Trolley dilemma B (photo credited to Jain, from Medium)

② Differences in the choices made between dilemma A and B

In the trolley dilemma A, it is said that a slightly higher population would have agreed to pull down the lever to save five men, when they are aware that this action will result in the death of one man. However, most of the people would refuse to push the one man off the platform when they are presented with the trolley dilemma B. Given the consequences in both cases are the same, i.e., kills one to save five or do not kill innocent other, why is there a difference in the choices we made?


As mentioned above, for extreme utilitarianism, if they believe that the outcome of killing one to save five maximizes the benefits, they would have pulled down the lever and pushed the fat man to save five people. Whereas for extreme deontology, they would have never broken the rules and harm innocent people, therefore they would let the trolley follow its original track.


Nevertheless, if you choose to pull down the lever in dilemma A, what exactly stops you from pushing someone off the platform when it comes to dilemma B? Well, the notion is called the Doctrine of Double Effect, and it basically states that it is ethically acceptable to do something morally good, even though it comes with a morally bad side-effect, and even if this bad side-effect is foreseeable (Clark, 2007).


There are some principles associated with the doctrine, and only with all four principles fulfilled, then the doctrine holds.

Table: Principles of the Doctrine of Double Effect

The nature-of-the-act condition. The outcome has to be morally good or indifferent, besides the foreseen evil. In this case, whether you pull down the lever or push the person off, you can save five people eventually.

The proportionality condition. The outcome has to be at least an equivalent of importance or benefit to balance off the action taken. In both scenarios, whether you pull down the lever or push the person off, you save five people by killing one.

The right-intention condition. You cannot take an action out of evil intention, even if the result is good. In both the dilemmas, whether you pull down the lever or push the person off, you are taking the action out of saving five people, but not because you want to kill that one person.

The means-end condition. To achieve the good outcome, the action taken must not have a bad effect. Or in other words, an evil act can never justify a greater good. Therefore, some people find that it is morally acceptable to do something for the greater good when the harm is unintended, i.e., pulling down the lever is not an evil act, and killing one person is foreseeable but unintended. However, it would be morally wrong to do something bad in order to reach a greater good, for instance, intentionally pushing someone to die to save five people.

③ In real life

Despite all the justification and doctrine, it is also important to know that a hypothetical judgement does not necessarily predict real-life behaviours, and it is important for you to consider the legal consequences of the trolley dilemma in real life. According to Bostyn, Sevenhant and Roets (2018), an assumption made in thought experiment predicts the affective and cognitive aspects of the decision itself, rather than suggesting our real-life action when encountered with such dilemmas. Therefore, when you are in such a situation and unsure of yourself, always seek help from the nearby practitioners and remember that you do not have the right to decide the lives of another under no circumstances.

As an extra question, let’s consider the following scenario. Using the trolley dilemma B again, but this time the fat man is the villain of putting the five hostages on the track. Now, would you do nothing and let the trolley kill the five men on the main track, or would you push the not-so-innocent villain in front of you onto the tracks to save the group? What will you do this time?

Figure 6: Trolley dilemma C (photo credited to Zarrella, from Quora)

④ In conclusion…

Of course, we have a lot of alternatives in real life if we are really trapped in this situation. After all, a moral dilemma is not meant to create a flawless solution, nor it is intended to reach a consensus among the public to follow just one conclusion. In fact, all the dilemmas presented above are just hypothetical thought experiments to utilize the philosophical concept in order to inspire or evoke our ideas and keep intellectual conversations going from time to time.


Last but not least, this moral paradox has been used as a mechanism to discuss the ethics of self-driving or autonomous vehicle design, in order to program the vehicle to choose whom or what to strike when a collision is unavoidable. Click the link below to be directed to Moral Machine, and by clicking on the “Judging” button, you will be presented with some moral dilemmas, in which you may have a try and make your own decisions. For a quick review on the whole concept of the trolley dilemma, click the link below to be directed to a TED-Ed video. You can also have a quick play on the trolley problem themed game below:


Bostyn, D. H., Sevenhant, S., & Roets, A. (2018). Of mice, men and trolleys: Hypothetical judgement versus real life behaviour in trolley-style moral dilemmas. Psychological Science, 29(7), 1084-1093. doi: 10.1177/0956797617752640

Clark, J. (2007). How the trolley problem works. How Stuff Works. Retrieved from

Foot, P. (1967). The problem of abortion and the doctrine of the double effect. Oxford Review, 5, 1-7. doi: 10.1093/0199252866.003.0002

Gawronski, B., & Beer, J. S. (2016). What makes moral dilemma judgements “utilitarian” or “deontological”? Social Neuroscience, 1-7. doi: 10.1080/17470919.2016.1248787

Mangan, J. (1949). A historical analysis of the principle of double effect. Theological Studies, 10(1), 41-61. doi: 10.1177/004056394901000102

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I am Teng Wen. I am currently an undergraduate student at HELP University, pursuing a major in Psychology. During my studies, I have found the elements of psychology fascinating, particularly in the field of research, counselling and clinical psychology. As I believe that “what is essential is invisible to the eye”, thus I see that time and value are two important pieces that truly help people to explore their inner self and then connect with each other emotionally.

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