Do Theological Claims Need to be Falsifiable?
Antony Flew’s famous 1950 article “Theology and Falsification” posed what came to be known as the “falsificationist challenge” to theology. A claim is falsifiable when it is empirically testable—that is to say, when it makes predictions about what will be observed under such-and-such circumstances such that, if the predictions don’t pan out, the claim is thereby shown to be false.
The idea that a genuinely scientific claim must be falsifiable had already been given currency by Karl Popper. Flew’s aim was to apply it to a critique of such theological claims as the thesis that God loves us. No matter what sorts of evil and suffering occur in the world, the theologian does not give up the claim that God loves us. But then, what, in that case, does the claim actually amount to? And why should we accept the claim? Flew’s challenge was to get the theologian to specify exactly what would have to happen in order for the theologian to give up the claim that God loves us, or the claim that God exists.
Now, there are several problems with Flew’s challenge. Some of them have to do with specifically theological matters, such as the analogical use of the term “good” when applied to God, the role that divine permission of evil plays in the realization of a greater good, and so forth. Some of the problems have to do with the idea of falsification itself. As Popper himself emphasized, it is simply an error to suppose that all rationally justifiable claims have to be empirically falsifiable. Popper intended falsificationism merely as a theory about what makes a claim scientific, and not every rationally acceptable claim is or ought to be a scientific claim. Hence not every rationally acceptable claim is or ought to be empirically falsifiable.
For example, the thesis of falsificationism itself is, as Popper realized, not empirically falsifiable. This does not make Popper’s falsificationist theory of science self-refuting, because, again, he does not say in the first place that every claim has to be empirically falsifiable. Falsificationism is a claim about science but it is not itself a scientific claim, but rather a philosophical claim (what Popper called a claim of “meta-science”). It is subject to potential criticism—by way of philosophical analysis and argument, say—but not by way of empirical testing, specifically.
Claims of mathematics and logic are like this too. We can analyze and argue about them philosophically, but they are not plausibly subject to empirical refutation, specifically. And metaphysical claims are like that as well. With at least the most general sorts of metaphysical claims (e.g. about the nature of causality as such, or substance as such, or what have you), it is a sheer category mistake to suppose that they do, or ought to, entail specific empirical predictions. The reason is that the claims are too general for that. They are claims about (among other things) what any possible empirically observable phenomena must necessarily presuppose (and any possible non-empirical realities too, if there are any). Naturally, then, they are not going to be undermined by any specific empirical observation. By no means does that make them immune from rational evaluation. They can still be analyzed, and argued for or against, by way of philosophical analysis and argumentation. But as with claims of meta-science, or claims of mathematics and logic, so too with claims of metaphysics, it is a mistake to suppose that they stand or fall with empirical falsifiability.
Now, the fundamental claims and arguments of theology—for example, the most important arguments for the existence and attributes of God (such as Aquinas’s arguments, or Leibniz’s arguments)—are a species of metaphysical claim. Hence it is simply a category mistake to demand of them, as Flew did, that they be empirically falsifiable. To dismiss theology on falsificationist grounds, one would, to be consistent, also have to dismiss mathematics, logic, meta-science, and metaphysics in general. Which would be, not only absurd, but self-defeating, since the claim that only scientific claims are rationally justifiable is itself not a scientific claim but a metaphysical claim, and any argument for this claim would presuppose standards of logic.
There is also the problem that, as philosophers of science had already begun to see at the time Flew wrote, it turns out that even scientific claims are not as crisply falsifiable as Popper initially thought. Indeed, the problem was known even before Popper’s time, and famously raised by Pierre Duhem. A scientific theory is always tested in conjunction with various assumptions about background conditions obtaining at the time an experiment is performed, assumptions about the experimental set-up itself, and auxiliary scientific hypotheses about the phenomena being studied. If the outcome of an experiment is not as predicted, one could give up the theory being tested, but one might also consider giving up one or more of the auxiliary hypotheses instead, or check to see if the background conditions or experimental set-up were really as one had supposed. That does not mean that scientific theories are not empirically falsifiable after all, but it does mean that falsifying a theory is a much messier and more tentative affair than readers of pop science and pop philosophy books might suppose.
Then there are claims that are empirical and not metaphysical in the strictest sense, but still so extremely general that any possible natural science would have to take them for granted—in which case they are really presuppositions of natural science rather than propositions of natural science. For example, the proposition that change occurs is like this. We know from experience that change occurs, but it is not something falsifiable by experience, because any possible experience by which we might test it itself presupposes that change occurs. In particular, in order to test a proposition via observation or experiment, you need to see whether or not your current experience is followed by the predicted experience, which involves one experience succeeding another, which entails change. Natural science itself, then, which involves attempting to falsify theories (even if it involves more than this) presupposes something which cannot be falsified.
Necessary presuppositions of natural science like the one just described are the subject matter of that branch of philosophy known as the philosophy of nature (which, though more fundamental than natural science, is less fundamental than metaphysics as Thomists understand “metaphysics,” and is thus something of a middle-ground discipline between them). For example, the Aristotelian theory of actuality and potentiality (which is the core of the Aristotelian philosophy of nature) is grounded in an analysis of what change must involve, where the existence of change is presupposed by natural science. Hence the theory of actuality and potentiality is grounded in what is presupposed by natural science. That is why even natural science cannot overthrow it. But the characteristically Aristotelian argument for God’s existence—the argument from change to the existence of an unchanging changer of things (or, more precisely, of a purely actual actualizer of things)—is grounded in the theory of actuality and potentiality, and thus in what natural science itself must take for granted. And thus it too cannot be overturned even by natural science. This “empirical unfalsifiability” is no more a weakness of the Aristotelian argument for God’s existence than the “empirical unfalsifiability” of the existence of change, including the existence of experience itself, is a weakness. It makes the arguments in question (if they are otherwise unproblematic) more rationally secure than empirical science, not less.
Lazy shouts of “unfalisfiability!” against theological claims just ignore all this complexity—the distinctions that have to be drawn between empirical claims on the one hand and claims of mathematics, logic, and metaphysics on the other; between extremely general empirical claims and more specific ones; between philosophy of nature (which studies the philosophical presuppositions of natural science) and natural science itself; and between the testing of a thesis and the testing of the auxiliary assumptions we generally take for granted but conjoin with the thesis when drawing predictions from it.
So, falsificationism is a rather feeble instrument to wield against theology. And in fact, atheist philosophers have known this for decades, even if New Atheist combox commandos are still catching up.
All the same, where we are evaluating a specific empirical claim—rather than a claim of mathematics, logic, or metaphysics, or an extremely general empirical claim like “change occurs”—falsifiability is an important consideration, even if not as decisive as Popper supposed. Take an extremely specific and straightforward empirical claim, e.g. the claim that a large, yellowish triangular shape will suddenly appear in the center of my field of vision within the next few seconds. If no such shape actually appears in the next few seconds, it would be pretty hard to deny that the claim has been falsified. For example, I couldn’t say “Maybe the shape was there in the room, but I didn’t see it because it was behind a bookshelf.” I intentionally phrased the claim so that it was about what I would experience, not about what would be in the room, so appealing to the idea that some physical object stood in the way of my seeing it won’t help avoid falsification. Nor would it help to say “Maybe it will appear an hour from now, or tomorrow,” since the claim referred specifically to the next few seconds.
Of course, that’s not a very interesting empirical claim. Most interesting empirical claims are far less specific than that, even though they are nowhere near as general as the claim that change occurs. There is, needless to say, a large range of cases, some of which are more toward the general end of things, some of them more toward the specific, and the latter are easier to falsify than the former. But even if the more general ones aren’t as crisply falsifiable as a more simplistic application of the Popperian model would imply, they are still far from unfalsifiable.
For example, take the claim that heavy smoking over a long period of time has a strong tendency to cause cancer. Obviously this is not falsified by the fact that some heavy smokers never develop cancer, because the claim has been phrased in a way that takes account of that. It speaks only of a strong tendency, and even a strong tendency needn’t always be realized. But neither is the claim made vacuous by that qualification. If it turned out that only five percent of people who smoke heavily over the course of many years ended up getting cancer, we could reasonably say that the claim had been falsified. Whereas if it turned out that sixty percent of those who smoke heavily over the course of many years end up getting cancer, we would say that the claim had survived falsification, even though sixty percent is well short of one hundred percent. Indeed, even if the percentage were much lower than that—suppose it were forty percent, for example—it would not necessarily follow that the claim had been falsified.
Nor need there be anything like even that strong a link between two phenomena for us reasonably to posit a causal correlation. Take an example often discussed in philosophy of science, viz. the relationship between syphilis and paresis. If syphilis is untreated, it can lead to paresis, though this is rare. But it would be absurd, not to mention medically irresponsible, to conclude that the claim of a causal correlation between syphilis and paresis is falsified by the fact that actually developing paresis is rare. All the same, if there were on record only one or two cases, out of millions, of paresis following upon syphilis, it would—especially if no mechanism by which the one might lead to the other were proposed—be hard in that case to resist the conclusion that the claim of a causal correlation had been falsified.
So, an empirical claim concerning a causal link between two phenomena can be substantive rather than vacuous, and also empirically very well-supported, even if there are many cases in which the one phenomenon is not in fact followed by the other. Considerations about falsifiability, properly understood, do not undermine the point. Indeed, someone who resists such a claim might himself be subject to criticism on the grounds that he has made his position unfalsifiable.
For example, suppose a heavy smoker said, in reply to those who implored him to cut back: “Oh come on, lots of people smoke heavily and don’t get cancer! So how can you maintain your claim that there is a causal link, in the face of all that evidence? Don’t you know that a serious scientific claim should be falsifiable?” In fact, of course, it is the heavy smoker in question who is more plausibly accused of being insufficiently respectful of falsifiability. For there is a very strong link between heavy smoking and cancer, even if the former doesn’t always lead to the latter. And the empirical evidence for that link is so strong that it is those who deny it who are refusing to let their position be falsified by the evidence.
More could be said, but in fact these reflections on falsification are intended merely as a preamble to an application of the idea to a domain very different from the examples considered so far—namely, an example concerning politics and current events. I’ll get to that in another post.
Written by Dr. Edward Feser
Dr. Edward Feser is Associate Professor of Philosophy at Pasadena City College in Pasadena, California. He has been a Visiting Assistant Professor at Loyola Marymount University in Los Angeles and a Visiting Scholar at the Social Philosophy and Policy Center at Bowling Green State University in Bowling Green, Ohio. He holds a doctorate in philosophy from the University of California at Santa Barbara, a master’s degree in religion from the Claremont Graduate School, and a bachelor’s degree in philosophy and religious studies from the California State University at Fullerton. He is author of numerous books including The Last Superstition: A Refutation of the New Atheism (St. Augustines Press, 2010); Aquinas (Oneworld, 2009); and Philosophy of Mind (Oneworld, 2007). Follow Dr. Feser on his blog and his website, EdwardFeser.com.
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Guest post by Hans Custers. Nederlandse versie hier.
A very, ehhrmm… interesting piece on
Variable Variability, Victor Venema’s blog: Interesting what the interesting Judith Curry finds interesting. And I don’t mean interesting in a rhetoric, suggestive way; I mean it is a well-written and well-reasoned article, worth reading.
Victor writes about the meme regularly used by the anti climate science campaign, often supported by some straw man arguments, that the science of human impacts on climate would not be falsifiable. He shows it’s nonsense, by giving some examples of how it could be falsified. Or, more likely, already would have been falsified, if the science would be wrong. Victor’s post inspired me to think of more options to falsify generally accepted viewpoints in climate science. If there are any ‘climate change skeptics’ who want to contribute to real science, they might see this as a challenge. Maybe they can come up with a research proposal, based on one of the options for falsification. Like proper scientists would do.
First, a few more things about falsifiability in general. Bart wrote a concise post about the subject four years ago, explaining that a bird in the sky does not disprove gravity. What looks like a refutation at first, might on second thoughts be based on partial or total misunderstanding of the hypothesis. Natural climate forcings and variations do not exclude human impacts. Therefore, the existence of these natural factors in itself, cannot falsify anthropogenic climate change. A real skeptic is cautious about both scientific evidence and refutations. ‘Climate change skeptics’ like to mention the single black swan, that disproves the hypothesis that all swans are white. Of course that is true, unless that single black swan appears to be found near some oil spill.
Some of the falsifications that I mention later on might be somewhat cheap, or far-fetched. It is not very easy to find options to falsify the science of human impacts on climate. Not because climate scientists don’t respect philosophical principles of science, but simply because there’s such a huge amount of evidence. There are not a lot of findings that would disprove all the evidence at once. A scientific revolution of this magnitude only happens very rarely. Whoever thinks differently, doesn’t understand how science works.
Even more, the claim ‘The AGW hypothesis is unfalsifiable’ demonstrates a lack of understanding of Popper’s ideas, in which falsifiability is so important. I don’t think Popper’s philosophy implies that some three word hypothesis – Anthropogenic Global Warming – can be rejected by nothing but a few simple claims. Popper would expect a more serious intellectual effort from a scientist. First, he will have to find an accurate wording for his hypothesis. The next step is some thorough thinking about the consequences. This will help him to design tests that can either support or falsify his idea. If, in the end, the result of the test appears to be worthwhile, the scientist will write a paper on this whole enterprise.
As a matter of fact, the ‘AGW-hypothesis’ is not a hypothesis in the Popperian sense. The human impact on climate is a theory, supported by many hypotheses, each of them tested according to widely accepted scientific standards. Just as Popper and his successors in the philosophy of science would have wanted.
One more thing. The philosophical principle of falsifiability and the feasibility of tests for it are two different subjects. Scientists are still busy testing some of the implications of Einsteins ideas, because the technology did not exist in Einstein’s days. And it is highly unlikely that the scientists that proposed the Higgs boson ever even dreamed of the Large Hadron Collider, because it was beyond anyone’s imagination at the time. Philosophy of science does not set a time frame for hypotheses testing. The issues involved in the testing of hypotheses are the story of almost every scientist’s life. They’re not sitting back, thinking of new and brilliant ideas, most of the time. Instead, they are busy digging for data, messing with measuring equipment, or evaluating errors in experiments. For climate scientists, one of the major issues is the pace at which they can get new information: one year of data every year. And one year of data is not a lot for climate research. There are no test tube planets for climate experiments. They will have to do with what is left: observations of (changes in) the climate in the present and the past and simulations of the relevant processes in the climate system in computer models. Most self-proclaimed skeptics seem to have objections to the latter as well. Wouldn’t it be nice if they, just for a change, would say how it should be done?
That’s it for falsifiability in general. Here are the 10 way to disprove the human impact on climate.
1. A drop in global temperatures for some period of time to the level of 50 years ago or longer, without a clear cause
The average global temperature is almost 1 °C higher now than it was in the early 20th century. The widget by Skeptical Science (which unfortunately does not work very well in a WordPress blog) adds some perspective to the amount of energy accumulating in the climate system. These huge amounts of energy do not simply stay in the climate system without a cause. It is what we expect to happen, based on the greenhouse theory. And there’s no other explanation that is supported by a reasonable amount of evidence. It would be very clear that science overlooked something important, if all the energy would suddenly escape without something extraordinary happening (like a huge volcanic eruption), or hide in some unknown place.
2. A drop in global sea level for some period of time
There are two major causes for sea level rise: thermal expansion of seawater and the melting of land ice. Water extraction from and (temporal) accumulation on land play a minor role. At this moment, thermal expansion is the main factor. This is evidence for warming of the oceans, which is important because the oceans can store much more heat than the atmosphere. Thus, the ocean level falling, would not only be evidence for cooling of the oceans; it would be strong evidence that the climate system as a whole would be losing energy. (Note: pure water has a strange property: the density decreases with an increase in temperature between 0 and 4 °C. This effect disappears with increasing salinity. For almost all sea water, the maximum density is at freezing point).
Changes in sea level on a short term are not caused by thermal expansion or contraction, so they do not falsify anthropogenic climate change. The figure below, from the University of Colorado’s Sea Level Research Group, for instance, shows a substantial seasonal variation. This variation can be filtered out of that data, and that’s the graph that is usually shown.
3. A strong rise or decline in the atmospheric CO2 level
Since the late 50’s, the Keeling Curve shows an ongoing rise in the amount of CO2 in the atmosphere. If there would be a sudden huge change in the CO2 level, without a clear, demonstrable cause, that would be proof that our knowledge of the carbon cycle falls short.
Climate change skeptics sometimes refer to a graph by Ernst-Georg Beck, in which thousands of megatons of CO2 mysteriously seem to appear in atmosphere within a few years, and then disappear again, causing wild fluctuations in CO2 levels. The fluctuations miraculously stop in 1958, exactly when Keeling started his measurements on Mauna Loa. Maybe we are being fooled for more than half a century by all CO2 molecules in the world. But it’s more likely that the graph below, from Cripps, father and son Keeling’s home base, displays the more accurate data.
4. The discovery that climate forcings in the past were much larger, or temperature changes much smaller, than science thinks
One of the ways to estimate climate sensitivity, is by looking at temperature changes in the past and the knowledge of their causes. It is very likely that the magnitude of a temperature change mostly depends on the magnitude of a change in the radiation balance at the top of the atmosphere, rather than the exact cause of this change. In other words: a Watt per square meter is a Watt per square meter, no matter if it comes from the sun, from an increased greenhouse effect, or something else. So, smaller temperature changes in the past, of larger forcings causing them, would be evidence for a low climate sensitivity.
Climate change skeptics often claim that relatively small change in the radiations balance are responsible for a significant part of the warming that we’ve seen since the early 20th century, or for temperature changes in a more distant past. They don’t seem to realize that these claims imply a higher, rather than a lower climate sensitivity than is generally assumed by scientists.
5. Warming of the stratosphere
Many changes that are happening in the climate system are caused by warming itself. Observations of these changes cannot be used as evidence for the cause of warming. But there are some changes – fingerprints – that are specific for the increased greenhouse effect. Cooling of the stratosphere is one of these fingerprints. This cooling is confirmed by measurements, as is shown in the figure below, from ‘State of the Climate 2012‘ by the Bulletin of the American Meteorological Society.
Stratospheric warming is not the only human fingerprint that can be found. More detailed information on fingerprints can be found in last year’s paper: ‘Human and natural influences on the changing thermal structure of the atmosphere‘ by Santer et al.
6. Major errors in equipment in satellites, measuring outgoing longwave radiation
We can see the absorption of heat by greenhouse gases in satellite measurements of longwave radiation that leaves the earth’s atmosphere. The absorption bands of CO2, methane, ozone and water vapor are clearly visible in these measurements, as shown in the figure below. Whoever can demonstrate the measurements to be wrong, will make it into the history books. It would not only disprove the human impact on climate, it would wipe quite a lot of established physical science off the table.
7. Evidence of a substantial fall of relative humidity with rising temperature
If specific humidity would not follow temperature, the relative humidity would be lower in a warmer world. Then, there would not be a positive water vapor feedback, or it would be very small. It is highly likely that this would make matters rather worse than better. Our greenhouse gas emissions would lead to a smaller rise in temperatures than expected, but the downside would probably be disastrous: world-wide drought. Unless Clausius and Clapeyron were wrong.
8. A source of heat in the climate system that we do not know yet
All the evidence shows the heat in the climate system has been increasing for decades, and still is. Assuming even climate change skeptics do not dispute the law of conservation of energy, there has to be a source of heat somewhere. Who knows, one day, we might find some kind of mini-sun, hidden deep in the oceans. It would be a game changer for climate science.
9. A fundamental flaw in the scientific understanding of radiation physics or thermodynamics
This one is especially for the ‘slayers’, who deny that there is a greenhouse effect at all. Their ideas are either utter nonsense, or they are about to discover the very biggest mistake in the history of science. It would mean that we’d have to reevaluate fundamental physical science, that has been undisputed for decades to centuries, like the Stefan-Boltzman law or even the laws of thermodynamics. We would probably end up rewriting every single physics book in the world.
10. CO2 molecules appear to behave differently in the wild, than they do in a laboratory
I added this last one as a ‘tribute’ to one of the veterans of the war on climate science in The Netherlands. He, whose name I will not mention, does not dispute the greenhouse effect, but thinks it is relevant to mention that absorption of longwave radiation by CO2 has only been measured ‘in laboratory conditions’. He’s wrong, of course, because there are satellite measurements as well. But let’s forget about that. I think the idea of molecules behaving differently in the lab, compared to their behavior in the wild, is so creative that it deserves attention. I won’t go into the consequences of this revolutionary hypothesis. I will leave that, dear reader, to your imagination.
Tags: Climate science, climate skeptics
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