Adam Smith Discovered (and Solved!) the Trolley Problem


The “trolley problem” was first stated in its modern form by Philippa Foot in 1967. I can’t possibly add anything useful to the mountain of analysis already published on the subject, so I’ll just state my version of the “problem” simply, so we all know what we are talking about.

Consider 3 scenarios:

1. A large heavy trolley car is hurtling down an incline. The braking system has failed. Ahead on the track is one person who will be killed if nothing changes. But you can save the person, because you can divert the trolley onto another track. However, if you do that the five people who are on the other track will be killed.

2. Same situation, except the current track has five people on it, and the diverted track has one person. If you do nothing five people will die; if you divert, one person will die.

3. Five people in a hospital will die tomorrow if they do not receive, respectively: (a) a heart transplant; (b) a liver transplant; (c) and (d) kidney transplants; and (e) a blood transfusion of a rare blood type. There is a sixth person in the hospital who, by astonishing coincidence, is an exact match as a donor for all five. If the head surgeon does nothing, five people will die tonight, with no hope of living until tomorrow. If the head surgeon gives the perfect donor a painless lethal injection, under the false pretext of administering helpful antibiotics, the blood and organs can be harvested and the five people will all live.

In terms of survey evidence based on these hypotheticals:

Almost everyone would choose to do nothing in scenario #1. It is troubling that you could have saved the person and chose not to, but taking an action that results in the death of five other people is clearly unacceptable. Of course, there have been variations—the one person is your son or daughter, or it’s you; what would you do then? Would you kill five strangers to save yourself or your child? Still, most people do nothing, or say they would do nothing.

Scenario #2 is more problematic. A bare majority (sometimes) would divert the trolley, killing one to save five. But there is a difference between failing to act and allowing a life to be taken, and actively taking a life by taking an intentional deadly action against someone who was otherwise in no danger. This difference is called “moral agency,” and means that though you might prefer the outcome “one person dies” over “five people die,” the fact that you are the one who must take causal agency and push the button, pull the trigger, or push the lever to cause the death changes the situation.

Scenario #3 is apparently “easy,” for most respondents: almost no one, perhaps not even Peter Singer himself, would actually forcibly murder the perfect donor patient to save the lives of the five who need transplants.

This all makes sense until you recognize that there is no real difference between scenarios #2 and #3 in terms of the social utilities involved. Why the large differences in the proportions of those who would act in scenario #2, but would not act in scenario #3? In both cases, you are intentionally acting to take a life to save five lives.

To be fair, many people have answered this question, in many different ways, and I am not in a position to contribute to that discussion which has likely passed the point of diminishing returns. It is still useful as a way of starting discussions in undergraduate PPE classes, of course. (Not that there is anything wrong with undergraduate PPE classes. If you are using the trolley problem for that purpose, you might be interested in Walter Block’s discussion of the “libertarian law” view, Steven Pinker’s contextualization in psychology, and the episode of “The Good Place” which forced more concrete considerations of the issues!)

What I want to do instead is propose a fourth scenario, one you may not have thought of in this way before. It goes like this:

4. Same situation (hurtling trolley, no brakes) as 1 and 2, except the current track has 100 million people on it, and the diverted track has your little finger stuck on the rail. If you do nothing 100 million people will die, but if you divert you will lose your little finger.

I know, that sounds ridiculous. But that, mutatis mutandis, is exactly the question posed by Adam Smith in a famous passage in Theory of Moral Sentiments. Smith asks what would happen if a “man of humanity in Europe” heard that there had been a terrible earthquake in distant China, which killed “a hundred millions of his brethren.” Smith imagined that the man would express genuine sorrow that this had happened, reflect on “the precariousness of human life, and the vanity of the labours of man, which could thus be annihilated in a moment.”

The man might also think about how this disaster might affect world politics, and the international economy, creating new opportunities for investment or rebalancing the man’s portfolio given the changed circumstances. But overall the distance, physical emotional, from the catastrophe would insulate the man’s feelings from any real discomfort or lengthy preoccupation. Smith makes a claim about human sentiments that seems monstrous, but which is perfectly plausible: we focus mostly on ourselves.

The most frivolous disaster which could befall himself would occasion a more real disturbance. If he was to lose his little finger to-morrow, he would not sleep to-night; but, provided he never saw them, he will snore with the most profound security over the ruin of a hundred millions of his brethren, and the destruction of that immense multitude [in the faraway earthquake] seems plainly an object less interesting to him, than this paltry misfortune of his own.

So, there’s the setup: People care more about their own misfortunes, even minor ones, than they do about the misfortunes of others, even major ones. Sounds like a perfect setup for the trolley problem, version #4, above. Specifically, if I care more about my own little finger than a hundred million strangers, would I divert the trolley?

Of course I would. That’s why I claimed that Smith “solved” the trolley problem, in the title of this piece.

To prevent, therefore, this paltry misfortune to himself, would a man of humanity be willing to sacrifice the lives of a hundred millions of his brethren, provided he had never seen them? Human nature startles with horror at the thought, and the world, in its greatest depravity and corruption, never produced such a villain as could be capable of entertaining it.

Even though in some sense I would be more upset at the prospect of losing my little finger than the prospect of a hundred million distant deaths, if I am placed in the position of moral agency I would immediately sacrifice my little finger. Smith zeroes in on the apparent paradox:

“But what makes this difference? When our passive feelings are almost always so sordid and so selfish, how comes it that our active principles should often be so generous and so noble?”

The fact that I “care more” about my little finger, in the sense that the prospect of loss upsets me more than hearing about a distant disaster, is not actually a preference where I rank the distant disaster above the loss of my finger. The reaction is emotional, not reasoned, and the reaction is also premised on the assumption I have no choice or agency in either event.

What’s really interesting is that Smith first claims that the reason we would divert the trolley (my words) to cut off our finger instead of killing a hundred million is that we are concerned what other people would think of us if we were selfish. But then he doubles down, and claims that the fundamental reason for our sacrifice would be what we think of ourselves. His language describing the resolution of the paradox is magnificent:

…It is not the soft power of humanity, it is not that feeble spark of benevolence which Nature has lighted up in the human heart, that is thus capable of counteracting the strongest impulses of self-love. It is a stronger power, a more forcible motive, which exerts itself upon such occasions. It is reason, principle, conscience, the inhabitant of the breast, the man within, the great judge and arbiter of our conduct…. It is not the love of our neighbour, it is not the love of mankind, which upon many occasions prompts us to the practice of those divine virtues. It is a stronger love, a more powerful affection, which generally takes place upon such occasions; the love of what is honourable and noble, of the grandeur, and dignity, and superiority of our own characters.

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