Socrates, Evolution, and the Word “Theory”


Photograph through Wikipedia by Greg O’Beirne, digitally altered to remove graffiti from forehead.

What’s wrong with this argument? More than you think!

All men are mortal.
Socrates is a man.
Therefore Socrates is mortal.

It’s perfectly valid, meaning that if the premises are true, the conclusion must also be true. Despite this, as Bertrand Russell explained very clearly many years ago,[1] the argument is almost totally worthless.

There is no real doubt that Socrates is mortal. Just look at the poor chap, clearly showing his 70 years. Bent, scarred from the Peloponnesian War, his brow furrowed by decades of unhappy marriage, and even more unhappy attempts[2] to persuade his fellow citizens that the best form of government is a fascist oligarchy. Besides, he is on trial for doubting the existence of the gods, and the news from the Agora is not good. Take my advice, and do not offer him life insurance.

Even if we didn’t know about his circumstances, we would readily agree that he is mortal. We see decrepitude and death around us all the time, few people have been known to live beyond a hundred years, none beyond 150, and we have no reason to believe that Socrates is any different. In fact, from our experience, we are a lot more certain that Socrates is mortal than we are that all men are mortal. Ganymede, Elijah, and the Virgin Mary were all, according to various traditions, taken directly up into heaven without having to go through the tedious process of dying. However, no Zeus-worshipper or biblical literalist or devout Catholic would for such reasons doubt the mortality of Socrates. So the premise, that all men are mortal, is actually less certain than the conclusion, and if we seriously doubted Socrates’s mortality, we would simply deny that premise. In other words, this classic example of deductive logic tells us nothing that we didn’t already know.

Gustave Doré: Elijah's Ascension

Ascension of Elijah, Gustave Dore’, ca. 1865

We have run up against a very general limitation of deductive arguments about the world. Our reason for believing in Socrates’ mortality is not really deductive, but inductive, reinforced in this case by our knowledge of his own personal circumstances. Logical arguments of this kind do indeed have an important place, but in and of themselves their conclusions tell us nothing new; nothing that was not already implicit in the premises. They are important, not because they give us new reasons for believing the conclusion (they don’t)[3], but because they force us to clarify our premises. Ultimately, what we get out of them is already implicit in what we put in.

With this in mind, let us examine an argument sometimes applied to evolution:

All theories are uncertain.
Evolution is a theory.
Therefore evolution is uncertain.

The standard response, which I have used myself, is to point out that the argument is fallacious because it involves an equivocation, or bait-and-switch, between two meanings of the word theory. It is like saying that if all lemons are yellow, and my car is a lemon, then my car must be yellow. In ordinary speech, perhaps, you only say “theory” when you are uncertain, but we are now talking about scientific theories, which include examples that no reasonable person would now seriously doubt, such as atomic theory or the heliocentric theory.

Sticker attached to textbooks in Cobb County, Georgia, from 2002 until removed by court order in 2006

And yet the argument really is alive and well. It was used, with deeply damaging effects on education in Turkey, by the then Minister of Education in the secular (!) government of the 1980s. Until 2001, the Alabama State Board of Education required biology textbooks carry a sticker saying “[M]acroevolution has never been observed and should be considered a theory.” Even where evolution is generally and officially acknowledge, it persists, and is used, by people who really should know better. There was a striking example recently on BBC TV, when the anchorman (Jeremy Paxman, who has a degree in English from Cambridge) turned portentously to Prof Alice Roberts, who was arguing against the teaching of creationism in schools, and actually uttered the words “Evolution is a theory”.

When, as here, a thoroughly bad argument persists in the face of what looks like a clear, much-repeated, logical refutation, when in addition it is readily expose as a piece of special pleading, when it is repeated in the media by intelligent and well educated people, and when it is even used to justify the actions of governments, it is worth asking why it has managed to survive.

There are several possibilities. The refutation may be emotionally unsatisfying, it may itself not stand up to close logical examination, or it may fail to address some deeper error which gave the fallacy its appeal in the first place. In any case, the correct response may be to bypass the fallacy by moving on as quickly as possible to the underlying facts. All of these, I maintain, applies to the “Evolution is a theory,” argument.

When confronted by Paxman, Prof Roberts responded in exactly the way I am advocating here. After saying that it was a theory like the Earth going round the Sun is a theory, she addressed herself to the factual evidence for evolution, leaving him floundering. That, I maintain, is the correct response. We should not waste time defending evolution from specious arguments, but go straight on to the attack by shifting the focus to the evidence.

As to why the two meanings defence fails to satisfy, the first reason to my mind is just this, that it is a defence, and thus gives unwarranted stature to the attack that it is meant to rebut. Qui s’excuse, s’accuse.

The second reason is that it feels like special pleading, and that feeling is at least in part justified. Words always carry with them a penumbra of possible meanings, and when Darwin speaks of “my theory” of the origin of species, or when Dalton spoke “my theory” of atoms, as they did, who are we to say that they were using words in the narrow technical sense that we assign to them now, after generations of subsequent discussion by philosophers of science?

Actually, it’s worse. Defenders of evolution have reacted to the “only a theory” argument by constructing their own implausible analysis of the word, and then upbrading the rest of us for not using it. To quote one of many examples, a much cited scientific American article reads

A scientific theory is an explanation of some aspect of the natural world that has been substantiated through repeated experiments or testing. But to the average Jane or Joe, a theory is just an idea that lives in someone’s head, rather than an explanation rooted in experiment and testing…  A word like ‘theory’ is a technical scientific term… The fact that many people understand its scientific meaning incorrectly does not mean we should stop using it. It means we need better scientific education.

How patronising and presumptuous! If people are misled by the creationist’s use of the term “theory,” it’s not up to us to use less ambiguous language; it’s their own fault for not being better educated. And if they are misled when we insist on using language in a specialised technical manner, that’s their fault, not ours!

And it gets worse yet. The claim being made here is not only arrogant but untrue. Even within technical scientific discourse, there is no built-in assumption that a theory has, by definition, been substantiated. We speak of phlogiston theory, even though we know it to have lacked substance, and of string theory, for which a test that could substantiate it has yet to be devised. We even speak of a “theory of everything”, although we do not as yet possess such a theory and some even doubt whether it is possible. We also speak of, and use, theories that we know to be strictly untrue. Ideal gas theory makes unrealistic assumptions about the properties and behaviour of gas molecules, but from this starting point goes on to make useful limiting predictions (Boyle’s Law, Charles’ Law, and a justification of Avogadro’s hypothesis) that to a good approximation do describe the behaviour of real gases under normal conditions. Newton’s theory of celestial motion is also strictly untrue, and fails to predict the precise behaviour of the planet Mercury. Nonetheless, we carry on using it to predict next year’s tides.

Worst of all, the two definitions defence no longer works even on its own terms. For the creationists, helped perhaps by their Intelligent Design colleagues, have discovered Popper. They now argue like him that if evolution is a scientific theory, in the technical sense that Scientific American and others are advocating, it must in principle be falsifiable. This as prelude to sliding, by innuendo, from falsifiable to uncertain. So this month, the State Board of Education of South Carolina is considering language that “requires students to understand that the theory of evolution, like any other scientific theory, may change as new scientific information is obtained.” And since 2012, the Alabama State Board has deployed a new disclaimer, which uses the seemingly innocent utterance

Scientific theories are based on both observations of the natural world and assumptions about the natural world. They are always subject to change in view of new and confirmed observations.

(but what assumtions do they have in mind, I wonder) to soften us up for the highly specific and inaccurate

The theory of evolution by natural selection is a controversial theory that is included in this textbook. It is controversial because it states that natural selection provides the basis for the modern scientific explanation for the diversity of living things. Since natural selection has been observed to play a role in influencing small changes in a population, it is assumed that it produces large changes, even though this has not been directly observed.

Of course large changes, as defined here, have not been directly observed, because by definition they need more time than scientists have been around to observe them. And of course the focus on what has been “directly observed” ignores multiple lines of evidence, each in itself conclusive. No matter. The State of Alabama still sees fit to single out evolution, telling its students that being a “scientific theory,” it is “subject to change”. Serve us right, for perpetrating the dangerous myth that there is something mysteriously different about science, that separates it from other areas of human activity. Of course our theories about evolution are “subject to change in view of new and confirmed observations”, but so is all our knowledge about the world.

Now of course neither the State of Alabama nor the State of South Carolina is seriously interested in the theory of evolution. They would not, for instance, be satisfied if we were to start telling students (as we should, and many of us do) that there has for more than 40 years been genuine controversy about the relative importance of natural selection and neutral drift. What they want to cast doubt on is the plain fact of common ancestry, and the implications of this for an ancient Earth. This is the solid ground on which we should be fighting, not the treacherous quagmire of terminology.[4]

When the creationists say “All theories are uncertain,” it looks as if they are making a factual statement about theories. If so, their argument would lose all credibility when we draw attention to other theories, such as atomic theory, which none would now contest. Yet it survives, because in yet another bait-and-switch, we are invited to assume that this uncertainty is part of the very definition of a theory. And so, if we are not careful, we find ourselves scrutinising the fine print of dictionaries, or, equally bad, coming up with the two meanings defence, which is itself another statement about definitions.

The absolutist (and creationists generally are absolutists) puts things in boxes, reads the label on the box, and uses what is written on the label to draw conclusions about the contents. Using two boxes instead of one sounds (is) artificial and defensive, and while it does sidestep the unwelcome conclusion, it commits the same logical error.

This error lies in pretending that we can answer a question of substance by examining the meaning of words. But the same error is present in the two meanings defence. Whether or not this or that definition of “theory” is correct, or is applicable in any particular case, has nothing to do with the real issue. Is evolution a theory? That depends on how you are using the word “theory.” Is evolution true? Yes.

[1] History of Western Philosophy, Ch. XXII

[2] Republic

[3] I suspect this really does apply to all simple syllogisms. More complicated examples are more interesting, rendering it important to distinguish between cases where the argument does generate new insights (e.g. theoretical physics), and those where it merely reinforces our original prejudices (economics, theology?)

[4] Didn’t we refute the creationist by pointing out that he has committed the fallacy of equivocation? Not so simple. As Boudry and Pigliucci point out (paper in preparation), naming a fallacy under conditions where anyone could credibly use it merely begs the question. Here, for example, we can only demonstrate that the equivocation is vicious by convincing the audience that evolution is not inherently uncertain. But that is what we have to do anyway!

I thank Maarten Boudry for access to unpublished material. An earlier version of this post appeared on 3 Quarks Daily.

About Paul Braterman

Science writer, former chemistry professor; committee member British Centre for Science Education; board member and science adviser Scottish Secular Society; former member editorial board, Origins of Life, and associate, NASA Astrobiology Insitute; first popsci book, From Stars to Stalagmites 2012

Posted on August 25, 2014, in Creationism, Philosophy, Education and tagged , , , , , , . Bookmark the permalink. 8 Comments.

  1. It seems to me that part of the problem is (also) that they enlarge the theory of evolution to include all the tested observations that the theory is created to explain. The theory is, in principle, falsifiable, but the observations are tested facts. Even if evolution by natural selection were in some (unimaginable?) way falsified, facts such as the change in life forms over time, extinction, successive change building on earlier change, deep time, etc. would require some explanation, and that explanation would NOT be the Biblical one favored by creationists, because it won’t do the explanatory work. But by expanding the “theory of evolution” to include its underlying facts, the creationists can misuse Popper to challenge the facts themselves.


  2. Very worthwhile post Paul.

    On a lighter note, when the creationists say “All theories are uncertain,”, should not the response be “including that one?”

    Best wishes!


  3. Regretful that such an essay has to even be written, but this is a marvelous, sadly necessary, treatment.


  4. Reblogged this on Peddling and Scaling God and Darwin and commented:
    Another good one from Paul


  5. It might be a relatively minor thing, but I think in the evolution/theory/uncertain syllogism, the bait-and-switch is more in the term “uncertain”. The first use on theories being uncertain is about well-quantified uncertainty. We know where theories don’t work, or can figure their limitations, and we know what predictions they make that have not yet been tested. We know theories are models, and models are subject to different spheres where they work. That’s one form of uncertainty. By contrast, the conclusion (presuming a hypothetical creationist is saying it) uses “uncertain” to mean that it could be valueless, without merit, or have no predictive power at all and can all be thrown out on a whim – which would never happen in a scientific theory because all scientific theories have explanatory power in the first place. As in practice, theories are “upgraded” rather than replaced (the development of atomic structure from the plum pudding to is current guise being a perfect example).

    I saw this exact argument pulled twice in quick succession just last week. And the board of education quote ““requires students to understand that the theory of evolution, like any other scientific theory, may **change** as new scientific information is obtained.” suggests this misunderstanding of development of theories, and how they’re judged to have uncertainty associated with them, is the core error.

    Either way, you’re right that a quibble over terminology of “theory” is something like a red herring.


  1. Pingback: Sahelanthropus, evolution, and the word “theory”; what Mike Pence really said | Primate's Progress

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