As Jim Croce once sang, “You don’t tug on Superman’s cape, You don’t spit into the wind, You don’t pull the mask off the old Lone Ranger, and you don’t match wits with David B. Hart.” (At least I think those are the lyrics, its been awhile since I heard the song.) Hart’s commanding intellect and depth of knowledge are so daunting that only the foolish would rush to disagree with him. While I’m naturally reticent to disagree with anything he writes, he made a claim about intelligent design theory (ID in his review of Richard Dawkin’s latest book that I believe is worth challenging.

Although I’m broadly skeptical about ID as it relates to biology (indeed, I broadly skeptical about how much we really know when it comes to the biological sciences), I have to take issue with this claim:

The best argument against ID theory, when all is said and done, is that it rests on a premise—“irreducible complexity”—that may seem compelling at the purely intuitive level but that can never logically be demonstrated. At the end of the day, it is—as Francis Collins rightly remarks—an argument from personal incredulity.

If this is truly the best argument against the theory, then ID is in very good shape.

Before we address whether irreducible complexity can be logically demonstrated, let’s examine the claim that it presents an argument from personal incredulity.

While Charles Darwin wasn’t aware of the term “irreducible complexity” he did posit it as a way to falsify his theory. In The Origin of Species , he wrote, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.” Opponents of ID naturally have a stake in dismissing irreducible complexity since it undercuts the primary challenge to Darwin’s theory. Labeling ID as an argument from personal incredulity or argument from ignorance is a shortcut to a showstopper: ID is guilty of this fallacy, ergo ID is false.

But what exactly is the fallacy being committed?

Although I can’t recall ever encountering an real live example of the argument from personal incredulity in the wild, the form is generally claimed to take one of the following forms:

1. There is no proof (or you have not proved) that p is false. Therefore p is true.
2. There is no proof (or you have not proved) that p is true. Therefore p is false.

But what’s wrong with this form? As philosopher Brandon Watson notes :

[I]t’s hard to see why this is fallacious; it is natural to read it as both defeasible and enthymematic. Walton, among others, has noted that as a matter of practical reasoning, this is often an excellent form of reasoning. (I have not determined that this gun is unloaded; it is reasonable to regard it as, for all practical purposes, a loaded gun unless it is shown to be otherwise.) But practical reasoning leaks into speculative inquiry; and as a purely speculative matter the above forms of reasoning can be quite reasonable. If I say, “There is no evidence that such-and-such drug has the effects attributed to it,” I am not appealing to ignorance. I am appealing to the evidence of the inquiries themselves , the inquiries that have been made into the effects of the drug in question, and it stands or falls with the adequacy of these inquiries. [italics in original]

Perhaps there are fallacious forms of the argument from ignorance, but if so they probably do not apply to ID. To see why, consider this thought experiment:
Yesterday I was on the moon. Since I was able to take my laptop and had a (really good) wireless Internet connection, I was able to send an email to NASA. Though I’m unclear on the process they used, they were able to verify that I was, to their great surprise, reporting from the lunar surface. When they asked me how I got there I told them that I couldn’t be completely certain, but I was pretty sure that I had walked to the moon.

As you can expect, they were rather skeptical despite the fact that they didn’t possess any reports of a spacecraft leaving earth’s atmosphere over the last 24-hour period. In fact, they didn’t have any evidence that would provide a suitable explanation at all for my journey. But while they could not come to a decisive conclusion about how I got there, they were sure of one thing: I didn’t walk to the moon.


Would I be justified in claiming that the NASA scientists were committing the fallacy of an argument from personal incredulity? Technically yes, according to the popular understanding of that so-called fallacy. But this runs counter to our intuitions—and for good reason: NASA would be quite justified in their skepticism.

Once we understand all the physical parameters and factors required to support my claim—the limitation of human feet, the lack of a walkway from earth to the moon, the superhuman speed and stamina required for the journey—we could reasonably conclude that even if we cannot absolutely rule out the possibility, we can render it extremely unlikely that I was able to walk from the United States to the Sea of Tranquility. Excluding this possibility doesn’t help us explain how I got up there but it does aid in understanding how I didn’t .

In essence the folks at NASA would examine the known parameters and posit an argument to the best explanation. Philosopher J.L. Mackie explains that these arguments share a common form:

The evidence supports the conclusion, it is suggested, because if we postulate that the conclusion is true—or better, perhaps, that it is at least an approximation to the truth—we get a more adequate overall explanation of that whole body of evidence, in light of whatever considerations are cited, than would be given by any available alternative hypothesis

While NASA has no positive evidence to support their conclusion they can use analogical reasoning and induction to rule out what is not possible, leaving them open to search for positive evidence on which to base an explanation. They can save time by ruling out the impossible in order to spend time searching for the probable.

ID theory follows a similar approach. ID advocates claim (with much justification) that the entire scientific community is clueless about the emergence of biological complexity and that the material mechanisms to which the biological community looks provides no clue how these systems might realistically have come about. Their claim is that certain features are irreducibly complex—that they are a single system composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning. They consider explanations that these structure arose by natural selection to be equivalent to my walk to the moon. And since they believe the natural parameters rule out the possibility of these complex structures arising solely by natural selection, they are warranted in searching for an alternate explanation.

Since there has been a gross explanatory failure in accounting for biological complexity I’m not sure why there is such opposition to considering this possibility. Obviously, if you are committed to atheistic materialism then you are less likely to consider evidence for intelligent design (though you should still be open to it). But why should theists be similar constrained? This research program may lead down a false path—but so has the current approach. Since biologists are unable to explain any complex biological functions without resorting to the language of teleology and design, you’d think they’d be more open to the possibility that actual teleology or design was involved in the process.

Nevertheless, there may be a strong case to be made against intelligent design theory. The entire concept may prove to be a complete waste of time and resources. If so the opponents of ID should make a positive case for how we rule out the design inference. Otherwise, they are merely presenting their own argument from personal incredulity.

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