On Certainty

Determining what we can and cannot be certain about regarding coronavirus

By Steve Humphrey
Illustration by Andrea Hutchinson

Except in trivial cases, certainty is mostly absent in science. Rene DesCartes famously searched for something of which he could be certain, and found it only in his slogan, Cogito, ergo sum, or “I think, therefore I am.” As I have explained in previous columns, the best we can hope for is a high degree of confirmation for our hypotheses, but no substantive theory can be verified or proven. All we can do is calculate the probability that some claim is true. 

Now, for some, a high probability can be quite comforting. When I read that, as of this writing, there have been fewer than 6,000 confirmed cases of coronavirus in the Commonwealth and fewer than 300 fatalities, given a population of some 4.5 million, the chance of contracting the virus is .0013. The chance of dying, even after having gotten the disease, is only 5%. This gives me great comfort. It is extraordinarily unlikely that I will die of the disease. But, for others, that extremely low probability is still pretty scary. What they would like is some assurance of certainty, that they will not, or even can’t, get or spread the virus. Unfortunately, such certainty is not available and will never be available. 

Some “experts” play on our fears by manipulating the data or noting that some hypotheses cannot be “proven.” For example, a while ago, the head of the World Health Organization announced that there was no evidence that the presence of antibodies conferred immunity upon someone who has survived the disease. Now, there are several things that can be said about this, aside from the fact that it is a dumb thing to say. For one, what would count as evidence for the claim, such that there is none available? It seems to me that if the claim that antibodies confer immunity is true, then we wouldn’t expect to see a large number of reinfections, and in fact, there have been very, very few. This is evidence. Further, there is also little, if any, evidence that the presence of antibodies does not confer immunity, and for the vast majority of coronaviruses (Sars-CoV-2 is the name of the virus that causes the disease COVID-19, and it is one of many similar viruses, all referred to as coronaviruses, that cause colds and flus), the presence of antibodies does provide immunity. Further, there are degrees of immunity, ranging from life-long total immunity to partial, short-lived immunity. So, while it is true that we can’t “prove” that immunity can be achieved, it is misleading to suggest that it can’t or won’t be. Finally, if epidemiologists really believed that immunity was impossible, why are they working on developing a vaccine? A vaccine is just an injection of weakened or dead viruses (or a surrogate for such) that is intended to provoke the body into developing antibodies to the virus. This is no different from having the disease and recovering from it. 

There is also the question of a “cost-benefit” analysis. We must balance the potential cost that our behaviors might engender against the benefit derived from those behaviors. This is difficult, if not impossible, to establish objectively, because it is a matter of values and values are subjective. For some, the benefit derived from being able to travel freely through the community is not worth the cost of contracting or spreading the disease. But this must be analyzed in terms of the probabilities. If getting the virus is very unlikely, and returning to a job would have great value, then loosening restrictions makes sense. But if you are not unhappy under quarantine and don’t need to get out to make a living, then the benefit does not outweigh the risk no matter how small. But I hope you can see why some people are chafing under the restrictions and protesting against them. For a public official, this is a nightmare: how to balance these incompatible, but equally rational, demands. 

This brings up another point. Suppose performing some action — wearing a mask, or gloves, or spraying some antiviral agent on everything you touch — would reduce your risk by some minimal amount. Suppose it would take your risk from .0013 to .001. Would it make sense to take those additional steps, especially if they became onerous? And, by taking more and more precautions, we can reduce the risk, but only by miniscule amounts. The rules for social distancing say stay six feet apart. Where did that number come from? Presumably, staying eight feet apart would reduce risk and 20 feet apart would reduce it even more. But nothing can guarantee that it would prevent infection.  

A final remark about certainty: certainty is a feeling, not a fact. Some feel so confident in their views that they are certain that they are right. Whereas they might be right, there is no certainty involved. Feeling certain is not the same as being certain, and the latter, as I have said, is virtually impossible. As my father used to say, “Only a fool is certain.”

Steve Humphrey has a Ph.D in the history and philosophy of science, with a specialty in philosophy of physics. He teaches courses in these subjects at the University of California, Santa Barbara, and has taught them at the University of Louisville.

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