In 1990 Judith Thomson published her book, The Realm of Rights. In it, she presented an elegant solution to the Trolley Problem. That is, she explained why there might be some principled exceptions to the general prohibition against killing others, even when that is necessary to save a larger number of lives.
The theory can be summarized as follows:
A policy P that will foreseeably kill one or more members of a group of persons G is permissible, if there was an earlier time when it was to everyone’s advantage for the policy P to be adopted.
In the Trolley case, Thomson makes vivid the hypothetical earlier time by asking us to imagine 6 track workers early in the morning, before they know whether they will be working alone or in a group of five. Provided the working positions they occupy will be determined randomly, all six workers will think it is in their interests to adopt a policy of killing one to save five: all six workers will obtain a greater chance of survival under this policy.
Of course, once the working positions are determined, the worker who is destined to work alone will not benefit from the policy. But Thomson thinks that any earlier time when it was to everyone’s advantage is enough to justify later killing in accordance with the policy.
Why does this account only give rise to a narrow range of exceptions, and not lead to killing in other cases such as the “fat man” variant on Trolley? Presumably, because there was no earlier time when the large individual would agree to the later kill one to save five policy. It is not to a large person, who doesn't work on trolley tracks, to agree to a later “kill large individuals in order to save track workers” policy. So the condition would not be satisfied. A similar story can be given about the Transplant case and similar scenarios.
Note also, Thomson’s view entails that the permissibility of killing in the original Trolley case is now going to depend on the prior history of how the individuals got on the tracks. If the one is a gardener employed by the trolley company, while the five are thrill seekers who ignored a sign warning against the danger of being on the tracks, pulling the lever is not permissible. (Presumably, some additional theory is required to translate these conflicting objective permissibility facts into a subjective permission for an ordinary agent who does not know how the people got on the track.)
In this video, I run through the account and explain its main features.
N.B. Thomson eventually abandoned this view, and I understand now regards it as always impermissible to kill one to save five. See “Turning the Trolley”. In a future post, I hope to discuss in detail the reasons she abandoned the view. Still, I think this is the best account that “solves” the trolley problem in its traditional form: explaining why trolley-type killing is permissible, without generalising to an absurdly large range of cases of killing one to save five. Her new view is effectively a denial that the problem can be solved at all.