I heard this fable from a philosopher dabbling in political theory:
Once upon a time, there were two nearby islands. Paul was the lone inhabitant of one island, and he had a small boat for fishing. Vivian was the lone inhabitant of the other, which hosted abundant stringy plants that she harvested for rope fiber. By working alone, they collected barely enough food for survival, but by cooperating they could gather 50 times as much.
Vivian had already spent an enormous amount of time weaving a few large nets out of plant fiber and Paul agreed to let her use his boat, but only if she gave him half of the fish. She agreed and gathered heaps of fish from the deeper waters. Before handing any fish over, Vivian reconsidered the fairness of dividing the fish equally. Vivian reasoned it was not fair for Paul to take half of the fish because he did not do any real work; he just let her use the boat. Paul reasoned that without his boat, Vivian would not have gotten the huge stock of fish, and anyway, she agreed to the deal beforehand.
This scenario illustrates the problem of cooperative surplus. Vivian and Paul each made a huge difference in the number of fish caught. 98 percent of the gathered fish can be attributed to Paul’s decision to lend Vivian the boat because if he had not, they would have caught 2 percent of what they actually caught. 98 percent of the gathered fish can be attributed to all of Vivian’s work because if she had not used the boat, they would have caught 2 percent of what they actually caught.
The problem is that there is no way for Vivian to get 98 percent of the fish and Paul to get 98 percent of the fish. The benefits of cooperation cannot be distributed to each actor in proportion to how much of a difference each made.
That is why other considerations are ordinarily taken into account. One consideration bearing on distributing the surplus fairly is the amount of effort each person expended. Another is that people can bargain for whatever proportion they like.
Interestingly, the structural features of this puzzle from political philosophy exist by virtue of the way causation works. We sometimes identify occurrences as causes because they make a difference to the occurrence of an effect. Other times we identify causes because they seem to help produce or generate the effect.
For example, consider a train that hauls coal from the mine to the steel mill. What caused the coal to arrive at the mill? One cause was that the train pulled it the whole way. The train made all the difference because if the train had remained at rest, the coal would not have moved anywhere. Yet, the straightness of the tracks made all the difference too. If the tracks had been too bent for the train to move, the coal would not have moved anywhere. The motion of the train and the straightness of the tracks are equal causes in the sense of making a crucial difference to the coal arriving.
In general, there is no reasonable way to distribute causal responsibility according to how much of a difference each causal factor made. As a result, we consider other factors, such as the fact that the train appears to be doing something, using fuel and driving its wheels forward, whereas the straightness of the tracks just remains there – seemingly inactive.
This example is one of many that illustrate the utility of understanding how causation works. It frequently turns out that difficult-to-resolve disputes inherit their problematic structure from general causal principles. By investigating causation, one can come to recognize where rational progress can be made and where opinions will likely remain at odds.
Douglas Kutach is visiting fellow at the Rotman Institute of Philosophy. His book Causation will be published in August