The Fallacy of Incommensurability

"if there's even one life that can be saved, then we've got an obligation to try."

"If there's anything we can do to save even one life… we should do that."

"One life lost on the job is one too many."

"If even one innocent person would be convicted, that's too many."

Frequently in speech about policies pertinent to human life and safety, one hears absolute claims such as the above. The true principle that "one may not do evil that good may come," is transformed into the seemingly plausible, but false principle "one must do everything possible to prevent such-and-such evil [e.g., innocent human death]". The plausibility of this principle derives from the fact that human life is, in a sense, of infinite value, so it seems that the loss of innocent human life can never be weighed up and considered as an altogether acceptable risk.

President Obama has on several occasions invoked such a principle to justify his positions. He even gives the impression that he actually believes the principle is valid, which would be a strong indication that he is quite incompetent to lead any community, let alone a country.

It is hard to know how genuinely any politician holds such a principle, since it seems to have settled so deeply into popular consciousness that it may be difficult for a politician to truthfully and rationally justify such decisions without risking being widely regarded as inhuman and inconsiderate. Imagine a politician publicly stating something like the following:

"This health-care legislation could be expected to save 1000 lives per year, but it would cost 12 billion dollars per year, and would a burden for doctors and other medical professionals; it's not worth it."

In actual fact, it is quite impossible to apply this principle consistently in practice, and attempting to do so leads to many contradictions. In almost every case, one of the things one could do to prevent certain bad things from happening would be to refrain from certain actions one is purportedly obliged to do in order to hinder other bad things.

Imagine, for example, that a city is deliberating whether to build a bridge over a large river. As the situation stands at present, 10,000 persons are driving daily on average 40 miles to work and back; with the new bridge, they would only need to drive an average of 20 miles. The construction of the bridge is expected to cost 20,000,000 dollars, and is estimated to have an 85% chance of involving at least one fatality for a construction work, and probably several.

Given that at least one death is expected in the construction of the bridge, it seems the city must forbid its construction. On the other hand, by constructing the bridge, 100,000,000 miles less would need to be driven per year, which over just ten years would save 15 lives. So, according to the principle that if something can be done to save even one life, one is obliged to do it, the city must build the bridge.

What will someone do who pretends or thinks that he abides by this principle of incommensurability? Who thinks that, because human life has a kind of infinite value, one can never consider an expected loss of human life to be an acceptable consequence of some policy? Faced by such a dilemma, he will either choose randomly, or in accordance with personal or basic human prejudices.  Most frequently, he will be inclined to over-rate probable and proximate events, and under-rate large but improbable and remote events. In the case of the bridge construction, he will likely underrate the importance of the deaths in traffic accidents that would be avoided by building the bridge, and overrate the importance of the deaths involved in the construction of the bridge.

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