A reader’s comment on my most recent post (”There’s nothing wrong with the Bible,” May 9, 2015) opined that “a thing does not ever really become a fact until all uncertainty is removed” and “where certainty ends, faith takes over to explore possible future outcomes not currently supported by facts.” He noted that “scientists are always upgrading ’facts’ with new evidence,” rendering the term “settled [science] problematic.”

Well, “problematic” is the natural state of humans who’d love to know, to be able to separate fact from conjecture, guesswork, lies, and simple errors. While I (and a few million others) argue that the scientific method is our most effective tool for separating out facts from beliefs and guesses, even facts discovered by the most rigorous science can be reversed in the face of new data or greater rigor. “We see through a glass darkly” is the human condition under the best of conditions.

Let me take issue not only with the commenter, but with my previous paragraph! He and I have blithely spoken of “fact” and “certainty,” as if we all mean the same thing by it or, indeed, that any one of us means the same thing at different times. One contribution of the scientific method is to teach us the value of doubt, to be ready to be shown that what we regard as fact is, in fact, not. In other words, it taught us that certainty is never fully removed. We deal in probabilities, at least our guesses about probabilities. I don’t mean our perception about things that are, apparently, truly probabilistic in nature (e.g., atomic decay or a hand of cards). I mean those characteristics of our universe that, we assume, are steady or fixed (e.g., the utility of algebra, the growth pattern of a plant, Boyle’s Law). Even those things we know only probabilistically.

In other words, we “know” only in differing amount of probability and those probabilities are themselves known only probabilistically. For example, I know the sun will come up tomorrow with more “certainty” than I know my Delta flight will actually get me to London. I know my wife loves me with more “certainty” than I know she will love me next year . . . and so forth on into all the “facts” our feeble minds can deal with. So if we wait for all uncertainty to be removed, we’ll be waiting a long time.

René Descartes tackled the problem by trying to find a logical point at which our knowledge is certain. He hoped he could then build on that certainty with further propositions. He came up with one that is, I’d wager, impossible to top: cogito ergo sum, “I think, therefore I am.” If I cannot trust my senses or my beliefs, at least I know there’s an “I” doing the doubting. In my opinion, having made a brave and brilliant start, Descartes then went off the rails with his next steps, adding assumptions that were patently arbitrary. But my point is that beyond that juncture of maximum certainty, we live in a world in which we can never be without uncertainty of some magnitude.

That is to say, certainty comes only in degrees. And it is the gradations we live with and learn to manipulate as part of living. We are “certain” that a second grader’s judgment about an airfoil design is less than an engineer’s. Can the engineer be wrong? Of course, due either to sloppy calculation or a new, as yet undiscovered principle of fluids. The certainty that a youth’s directions to some local site will get us there is less, we’d say, than directions given us by a fire fighter or cop. It is in this way that “settled science” does have utility as a shorthand term, differentiating a scientific finding that has endured many unsuccessful attempts to falsify (that is, disprove) it versus one that has fewer. A bit sloppy as a term? Yes, it is, but “settled science” is a shorthand rarely used by scientists except when the attempts to falsify the position in question are exceptionally numerous. The acceleration of gravity, evolution by natural selection, and quantum theory are examples of “settled science,” rather than propositions which have not endured a multitude of research testing. But if by “settled science” one means the level of certainty of cogito ergo sum, then it is being used wrongly.

“Where certainty ends,” the commenter wrote, “faith takes over to explore possible future outcomes not currently supported by facts.” Well, maybe. The normal progression is that observations are made (possibly by accident) that taken together suggest a hypothesis that goes beyond them and might explain them. I suppose an experimenter could have such strong opinion about one or more hypotheses such that his or her mindset could reasonably be called “faith,” but that would be quite unusual. In any event, testing the hypothesis consists in whether it accurately predicts observations not yet made, but “hypothesized,” i.e., predicted by the hypothesis. If its prediction of new observations works, then we might have something. Might. For all we will have done is fail to falsify the hypothesis; we have not proven it.

In non-scientific life, it is at this stage we often go awry. We consider the hypothesis (OK, our guess) to be true if its predictions come true. But all this small success means is that we have not proven the hypothesis to be wrong, that is, we haven’t falsified it. Many further failed attempts to falsify the hypothesis certainly raises the probability that the hypothesis is true, but as I pointed out earlier, in the strictest terms, it is never perfectly proven. Another hypothesis might come along with even greater predictive power. Now, in normal life we’d have consented to treating the hypothesis as “fact” some time ago in the process.

(As an aside, this seems a good spot to point out that one of the problems with religions is that very few hypotheses garnered from it are open to falsification. It is like saying there is an invisible frog than exists only where no human instrument or sense can detect it. Could be true. But if false, you’d never find out.)

A theory is even more demanding than a hypothesis for it embraces multiple hypotheses. Einstein’s theory of gravity, Darwin’s theory of evolution by natural selection, and Wegener’s theory of continental drift are well-known theories. (Uninformed persons often make the mistake of referring to a scientific theory as if “theory” means no more than an extensive guess. Such references have been frequent in the American politicization of evolution.) But no matter how advanced our science, knowledge goes from rung to rung, not from ignorance to perfect knowledge is a single inspired leap. Sometimes a rung adds more precision to the previous rung; sometimes it totally reverses it. And while scientists are elated by the latter (how exciting it was when Einsteinian gravity informed and in some ways replaced Newtonian gravity!), anti-scientists see it as proof that science is less to be trusted than their intuition and their religion—for since religion’s claims come ostensibly from an unimpeachable source, it can’t be wrong and therefore can’t be changed.

The “God package,” as the philosopher Bertrand Russell called it, still keeps shrinking as the scientific tortoise continues to keeps making incremental changes in our understanding of the universe—one carefully considered step at a time, continuing to surpass the religious rabbit so bent on once-and-for-all sweeping scenarios of heaven and earth in one divine breadth.

I’ll make only a short rejoinder to the commenter’s reference to “defenders of ‘climate change’” pushing “their agenda.” That comment suggests that the commenter has a strong opinion about global climate change, a position that can only be arrived at by (a) a meteorological scientist or by (b) adopting a political position on the matter. While the former is legitimate, it is surely lonely. If the latter, it has value for a science-ignorant electorate and therefore has partisan utility, but none for forming a rational opinion. Allow me to reiterate the point made in “Science and society—separating the roles” that I posted on this blog on October 2, 2013:

Scientists are the best sources to define science and to define what legitimate science has found. Can they err? Of course, but they are the most qualified source we have. They can certainly do so better than press or, especially, politically partisan news sources, politicians, and partisans. At any rate, because scientists sometimes disagree, the rest of us have no intelligent choice but to follow the scientific consensus—the consensus, not individuals who say what we’d like to hear. In the climate change matter, there are innumerable unqualified persons on both sides ready to quote from sun spot data, atmospheric chemistry, and other matters that support their politicized point of view.

So what do the scientists and scientific organizations say? Whatever they say, it is more qualified than my commenter’s or my unqualified statements. Here are a few sources (there are more), along with dates to show this is not new information:

• American Association for the Advancement of Science: “The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society.” (2006)
• American Chemical Society: “Comprehensive scientific assessments of our current and potential future climates clearly indicate that climate change is real, largely attributable to emissions from human activities, and potentially a very serious problem.” (2004)
• American Geophysical Union: “Human‐induced climate change requires urgent action. Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes.” (Adopted 2003, revised and reaffirmed 2007, 2012, 2013)
• American Medical Association: “Our AMA . . . supports the findings of the Intergovernmental Panel on Climate Change’s fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant.” (2013)
• American Meteorological Society: “It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide.” (2012)
• American Physical Society: “The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth’s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now.” (2007)
• The Geological Society of America: “The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2006), and the Intergovernmental Panel on Climate Change (IPCC, 2007) that global climate has warmed and that human activities (mainly greenhouse‐gas emissions) account for most of the warming since the middle 1900s.” (2006; revised 2010)

Certainty—unless it means a highly probable description of reality—is simply not available to us. It is inviting, I do understand, to adopt political, religious, or personal positions as if they are certainties. Religion and politics offer many possibilities to persons more bent on feelings of certainty than on the integrity of their understanding.