Don Howard
We are all Humeans, all of us who are trained in science, at least. We know that empirical evidence confers at most high probability, never certainty, on a scientific claim, and this no matter how sophisticated the inductive logic that we preach. Enumerative induction doesn’t do it. That the sun rose every day in recorded history and before does not imply that it will, of necessity, rise tomorrow. Inference to the best explanation doesn’t do it, for such inferences depend on a changing explanandum (that which is to be explained) and upon both an obscure quality metric (what determines the “better than” metric) and a never complete reference class of competing explanations. Bayes’s theorem can’t do it either.
No. All of us who are trained in science know that every theory, principle, law, and observation is open to challenge and that many once thought secure now populate the museum of dead theories. Sophisticated philosophers of science have invented the intimidating name, “the pessimistic meta-induction” for the thesis that, just as all theories in the past have turned out to be false or significantly limited in scope, so, too, most likely, will our current best and future science.
No. We all know that science is a matter of tentative hypotheses and best guesses. Some principles that have proven their mettle over the long haul, such as the conservation of energy, rightly earn our confidence that they can be reliable guides in the future. But more than one scientist has been willing to sacrifice even the conservation of energy if that were the price to solve another intractable riddle, as when Niels Bohr twice proposed theories that assumed violations of energy conservation.
That science does not deal in certainty is a major part of what makes it such a precious cultural achievement. Science is not dogma. Science admits its failings and learns from its mistakes. That it does so is key to how it achieved the dramatic expansion of scientific understanding that we have witnessed at least since the Renaissance.
Why, then, do we have so much trouble speaking honestly to the public about uncertainty? Why, when debating on the campaign trail, do we give in to the temptation to describe anthropogenic climate change as “proven fact.”? Why, when on the witness stand, do we feel the need to assert that a Darwinian story about human origins is established “beyond all reasonable doubt”? We have lots of good reasons for believing in human-caused climate change and Darwinian evolution. Few scientific claims are as well established as these. But about both we might be wrong in some as yet unforeseen or unforeseeable way. Why lie? Why not speak honestly?
There are at least two reasons why, when speaking to the public, we so often seek refuge in the rhetoric of proof and truth. The first is that we wrongly think that the scientific laity cannot understand uncertainty and probability. This is one of the most worrisome ways in which we insult the intelligence of our audience.
That lots of us – scientists and non-scientists alike – make lots of inductive and probabilistic mistakes is obvious. Casinos, state lotteries, and race tracks are all the evidence one needs. They profit only thanks to those mistakes. Nor are any of us rational utility maximizers, soundly weighing expected gains and losses against the probabilities of various outcomes. The stock market provides the relevant evidence here.
But the fact that lots of people make inductive errors doesn’t imply that the educated public can’t deal with uncertainty. We all deal with uncertainty all the time, and, in the main, we do a good job with it. Do I take I-294 or the Skyway, the Dan Ryan, and the Kennedy to O’Hare? What are the odds of congestion on each at this time of day? How much of a time cushion do I have? What are the consequences of being early or late? How likely am I to miss my flight if there is a ten-minute delay, a twenty-minute delay, or an hour-long delay? Chance of rain? Do I take the umbrella or also my overcoat? Much of life is like this. We make mistakes, but we get by, don’t we?
The second major reason why we retreat to the rhetoric of proof and truth is that we allow ourselves to be intimidated by the merchants of doubt.* The political exploitation of uncertainty to create the illusion of scientific dissensus and thereby stymie policy making on global warming, public health, energy, and other issues is now, itself, big business. There are lobbying firms, fictitious “think tanks,” corporate public relations offices, sham public interest groups, and members of congress who might as well be paid spokespersons. Much of the same kind of apparatus is encountered in the “debates” over evolution and intelligent design. Acknowledge uncertainty, and that becomes the wedge by means of which the illusion of scientific controversy can be created where there is, in fact, no controversy. What is to be done?
What is not to be done is misrepresenting the contingency of science. It is a mistake to confront the merchants of doubt with the pretense of certainty and proof. The right response is to trust the public to understand the weighing of evidence and the adjustment of policy to the strength of the evidence. The right response is, simply and clearly, to present the evidence. To be sure, climate modeling and population genetics involve sophisticated statistical tools that cannot be explained in detail in a few sentences. But with only a bit effort one can usually explain the general issue in an accessible manner.
A good example of making probabilities accessible is the recent reporting on the hunt for the Higgs boson with the Large Hadron Collider at CERN. Any reader of the New York Times or the Wall Street Journal now knows the expressions “three-sigma” and “five-sigma.” A tutorial on calculating standard deviations was not needed to communicate the point that, when sorting through oceans of data, looking for truly exceptional events, one wants to be sure that what one is seeing is more than what would be expected from random fluctuations. People understand this. If the roulette ball lands on 36 twice in a row one is mildly surprised but doesn’t accuse the croupier of cheating. If it lands on 36 five times in a row, then it’s time to ask to see the manager.
No contentious policy questions turn on the results from CERN, so perhaps it is easier for us to speak about uncertainty in this context. But if we can educate the public about statistics in particle physics, surely we can do it as well when the topic is flu epidemics or vehicle safety or climate change. Here is the evidence for increased global temperatures over the last century. Here is what the models predict for increased sea levels. Here is our degree of confidence in these predictions. Now let’s talk about the costs and benefits of different courses of action. Be firm. Be clear. Don’t be afraid to call a lie a “lie” when others misrepresent the evidence or misdescribe the models. But trust the public to follow the logic of the science if we do a good enough job of explaining that logic.
There might be one final reason why we too often retreat to the rhetoric of proof and truth, a reason that I’ll just mention here, saving a fuller discussion for another occasion. It is that too many of us were, ourselves, badly trained in science. Too many textbooks too many courses, and far, far too many popular science writers still teach the science in ways that encourage the illusion of settled fact where there is none. Thomas Kuhn taught us that science teaching often looks more like indoctrination than we might be comfortable acknowledging. There are remedies for this, foremost among them a more thorough and sophisticated incorporation of history and philosophy of science into science pedagogy. But, again, that is a topic for another post.
*See the excellent book by this title: Naomi Oreskes and Eric Conway, Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming (Bloomsbury Press, 2010).