Why scientific theories are more than explanations

(I will be traveling for a few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)

At its heart, intelligent design creationism (IDC) advocates adopt as their main strategy that of finding phenomena that are not (at least in their eyes) satisfactorily explained by evolutionary theory and arguing that hence natural selection is a failed theory. They say that adding the postulate of an ‘intelligent designer’ (which is clearly a pseudonym for God) as the cause of these so-called unexplained phenomena means that they are no longer unexplained. This, they claim, makes IDC the better ‘explanation.’ Some (perhaps for tactical reasons) do not go so far and instead say that it is at least a competing explanation and thus on a par with evolution.

As I discussed in an earlier posting, science does purport to explain things. But a scientific explanation is more than that. The explanations also carry within themselves the seeds of new predictions, because whenever a scientist claims to explain something using a new theory, the first challenge that is thrown invariably takes the form “Ok, if your theory explains X under these conditions, then it should predict Y under those conditions. Is the prediction confirmed?”

If the prediction Y fails, then the theory is not necessarily rejected forever but the proponent has to work on it some more, explain the failure to predict Y, and come back with an improved theory that makes better predictions.

If the prediction Y is borne out, then the theory is still not automatically accepted but at least it gains a little bit of credibility and may succeed in attracting some people to work on it.

Theories become part of the scientific consensus when their credibility increases by these means until they are seen by the scientific community to be the exclusive framework for future investigations. A scientist who said things like “My new theory explains X but makes no predictions whatsoever” would be ignored or face ridicule. Such theories are of no use for science.

And yet this is precisely the kind of thing that IDC proponents are saying. To see why this cannot be taken seriously, here is something abridged from the book Physics for the Inquiring Mind by Eric Rogers (p. 343-345), written way back in 1960. In it Rogers looks at competing claims for why an object set in motion on a surface eventually comes to rest:


The Demon Theory of Friction

How do you know that it is friction that brings a rolling ball to a stop and not demons? Suppose you answer this, while a neighbor, Faustus, argues for demons. The discussion might run thus:

You: I don’t believe in demons.
Faustus: I do.
You: Anyway, I don’t see how demons can make friction.
Faustus: They just stand in front of things and push to stop them from moving.
You: I can’t see any demons even on the roughest table.
Faustus: They are too small, also transparent.
You: But there is more friction on rough surfaces.
Faustus: More demons.
You: Oil helps.
Faustus: Oil drowns demons.
You: If I polish the table, there is less friction and the ball rolls further.
Faustus: You are wiping the demons off; there are fewer to push.
You: A heavier ball experiences more friction.
Faustus: More demons push it; and it crushes their bones more.
You: If I put a rough brick on the table I can push against friction with more and more force, up to a limit, and the block stays still, with friction just balancing my push.
Faustus: Of course, the demons push just hard enough to stop you moving the brick; but there is a limit to their strength beyond which they collapse.
You: But when I push hard enough and get the brick moving there is friction that drags the brick as it moves along.
Faustus: Yes, once they have collapsed the demons are crushed by the brick. It is their crackling bones that oppose the sliding.
You: I cannot feel them.
Faustus: Rub your finger along the table.
You: Friction follows definite laws. For example, experiment shows that a brick sliding along a table is dragged by friction with a force independent of velocity.
Faustus: Of course, the same number of demons to crush however fast you run over them.
You: If I slide a brick among a table again and again, the friction is the same each time. Demons would be crushed on the first trip.
Faustus: Yes, but they multiply incredibly fast.
You: There are other laws of friction: for example, the drag is proportional to the pressure holding the surfaces together.
Faustus: The demons live in the pores of the surface: more pressure makes more of them rush out and be crushed. Demons act in just the right way to push and drag with the forces you find in your experiments.

By this time Faustus’ game is clear. Whatever properties you ascribe to friction he will claim, in some form, for demons. At first his demons appear arbitrary and unreliable; but when you produce regular laws of friction he produces a regular sociology of demons. At that point there is a deadlock, with demons and friction serving as alternative names for sets of properties – and each debater is back to his first remark.


Faustus’s arguments are just like those of the IDC advocates, and the reason why they are consistently rejected by the scientific community. Scientists ask for more than just explanations from their theories. They also need mechanisms that make predictions. They know that that is the only way to prevent being drowned in an ocean of ‘explanations’ that are of no practical use whatsoever.

You can’t really argue with people like Faustus who are willing to create ad hoc models that have no predictive power. Such explanations as he gives have no value to the practicing scientist. But when you walk away from this kind of fruitless pseudo-debate, you do allow the other side to charge that you are afraid to debate them, at which point, they may jump up and down and shout “See they cannot refute us. We win! We win!”, however illogical the charge.

It reminds me of the duel scene in Monty Python and the Holy Grail in which King Arthur chops off the arms and legs of the Black Knight, leaving just his torso and attached head on the ground, totally defenceless. The Black Knight refuses however to concede defeat and offers a compromise: “Oh? All right, we’ll call it a draw.” When Arthur and his assistant walk away from this offer, the Black Knight starts taunting him saying “Oh. Oh, I see. Running away, eh? You yellow bastards! Come back here and take what’s coming to you. I’ll bite your legs off!”

At some point, in order to save your time (and your sanity) you have to simply walk away and ignore them. This explains why so many scientists refuse to get involved in the IDC battles.

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Why IDC is not science

(I will be traveling for a few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)

In the previous posting, I pointed out that if one looks back at the history of science, all the theories that are considered to be science are both (1) naturalistic and (2) predictive. Thus these two things constitute necessary conditions.

This is an important fact to realize when so-called intelligent design creationism (IDC) advocates argue that theirs is a ‘scientific’ theory. If so, the first hurdle IDC must surmount is that it meet both those necessary criteria, if it is to be even eligible to be considered to be science. It has to be emphasized that meeting those conditions is not sufficient, for something to be considered science, but the question of sufficiency does not even arise because IDC does not meet either of the two necessary conditions.

I issued this challenge to the IDC proponents when I debated them in Kansas in 2002. I pointed out that nowhere did they provide any kind of mechanism that enabled them to predict anything that anyone could go out and look for. And they still haven’t. At its essence, IDC strategy is to (1) point to a few things that they claim evolutionary theory cannot explain; (2) assert that such phenomena have too low a probability to be explained by any naturalistic theory; and (3) draw the conclusion that those phenomena must have been caused by an ‘unspecified designer’ (with a nudge, nudge, wink, wink to the faithful that this is really God) whose workings are beyond the realm of the natural world explored by science.

Thus they postulate a non-natural cause for those phenomena and cannot predict any thing that any person could go and look for. (This is not surprising. The designer is, for all intents and purposes, a synonym for God and it would be a bit bizarre to our traditional concept of God to think that his/her actions should be as predictable as that of blocks sliding down inclined planes.) When I asked one of the IDC stalwarts (Jonathan Wells) during my visit to Hillsdale College for an IDC prediction, the best he could come up with was that there would be more unexplained phenomena in the future or words to that effect.

But that is hardly what is meant by a scientific prediction. I can make that same kind of vague prediction about any theory, even a commonly accepted scientific one since no theory ever explains everything. A scientific prediction takes the more concrete form: “The theory Z encompassing this range of phenomena predicts that if conditions X are met, then we should be able to see result Y.”

IDC advocates know that their model comes nowhere close to meeting this basic condition of science. So they have adopted the strategy of: (1) challenging the naturalism condition, arguing that it is not a necessary condition for science and that it has been specifically and unfairly adopted to exclude IDC from science; and (2) tried to create a new definition of science so that IDC can be included. This takes the form of arguing that a scientific theory is one that ‘explains’ phenomena.

There are variations and expansions on these arguments by the various members of the IDC camp but I have tried to reduce it to its skeletal elements. These variations that IDC proponents adopt are designed to blur the issues but are easy to refute. See this cartoon by Tom Tomorrow (thanks to Daniel for the link) and this cartoon (thanks to Heidi) and this funny post by Canadian Cynic about the possible consequences of using IDC-type reasoning in other areas of life.)

The rejection by IDC advocates of naturalism and predictivity as necessary conditions for science goes against the history of science. Recall for example the struggle between the Platonic and Copernican models of the universe. Remember that both sides of this debate involved religious believers. But when they tried to explain the motions of the planets, both sides used naturalistic theories. To explain the retrograde motion of Mercury and other seemingly aberrant behavior, they invoked epicycles and the like. They struggled hard to find models that would enable them to predict future motion. They did not invoke God by saying things like “God must be moving the planets backwards on occasion.” Or “This seemingly anomalous motion of Mercury is due to God.” Such an explanation would not have been of any use to them because allowing God into the picture would preclude the making of predictions.

In fact, the telling piece of evidence that ended the geocentric model was that the Rudolphine Tables using Kepler’s elliptical orbits and a heliocentric model were far superior to any alternative in predicting planetary motion.

While it may be true that the underlying beliefs that drove people of that time to support the Platonic or Copernican model may have been influenced by their religious outlook, they did not seem to invoke God in a piecemeal way, as an explanation for this or that isolated phenomenon, as is currently done by IDC advocates. Instead they were more concerned with posing the question of whether the whole structure of the scientific theory was consistent with their understanding of the working of God. In other words, they were debating whether a geocentric model was compatible with their ideas of God’s role in the world. The detailed motions of specific planets, however problematic, seemed to have been too trivial for them to invoke God as an explanation, although they would probably not have excluded this option as something that God was capable of doing.

It may also well be true that some scientists of that time thought that God might be responsible for such things but such speculations were not part of the scientific debate. For example, Newton himself is supposed to have believed that the stability of the solar system (which was an unexplained problem in his day and remained unsolved for about 200 years) was due to God periodically intervening to restore the initial conditions. But these ideas were never part of the scientific consensus. And we can see why. If scientists had said that the stability was due to God, and closed down that avenue of research, then scientists would never have solved this important problem by naturalistic means and thus advanced the cause of science. This is why scientists, as a community, never accept non-natural explanations for any phenomena, even though individual scientists may entertain such ideas.

So the attempts by IDC advocates to redefine science to leave out methodological naturalism and predictivity fly completely in the face of the history of science. But worse than that, such a move would result in undermining the very methods that has made science so successful.

In the next posting, we will see why just looking for ‘good’ explanations of scientific phenomena (the definition of science advocated by the IDC people) is not, by itself, a useful exercise for science.