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In this week’s eSkeptic, Robert Camp explores the validity of William Dembski’s argument from analogy for Intelligent Design. William Dembski is a senior fellow with Discovery Institute’s Center for Science & Culture, and is a leading proponent of Intelligent Design.

Can Intelligent Design be considered scientific in the same way that SETI is?

by Robert Camp

”Some things have to be believed to be seen.”
—Ralph Hodgson

One of the most ubiquitous rhetorical devices used by “Intelligent Design” (ID) theorists in support of their ideas is the argument from analogy with human designs and endeavors. These analogies have been many and varied, ranging from the rather fanciful “bulldozer on Jupiter” metaphor to comparisons of ID with scientific disciplines such as SETI and criminological forensics. I recently ran across two instances of such a device, one in the first paragraph of William Dembski’s testimony submitted to the recent Texas textbook hearings,

Real life SETI researchers have thus far failed to detect designed signals from distant space. But if they encountered such a signal, as the astronomers in Sagan’s novel did, they too would infer design.1

Dembski has elaborated on this analogy,

To say intelligent causes are empirically detectable is to say there exist well-defined methods that, based on observable features of the world, can reliably distinguish intelligent causes from undirected natural causes. Many special sciences have already developed such methods for drawing this distinction — notably forensic science, cryptography, archeology, and the search for extraterrestrial intelligence (SETI). Essential to all these methods is the ability to eliminate chance and necessity.2

Use of examples such as these is obviously calculated to give design theory, and particularly Dembski’s “Explanatory Filter,” an air of significance and legitimacy. As noted by philosopher Robert Pennock,

In a clever rhetorical move, they frequently quote the late astronomer and SETI pioneer Carl Sagan to show that even a confirmed skeptic such as he admitted that such investigation is scientifically legitimate.3

Evolutionary biologist Massimo Pigliuscci points out that even if the analogy is considered accurate, Dembski’s point is undercut by the fact that natural causes can produce results that make a determination of “Intelligent Design” extraneous from a scientific perspective.

Dembski is absolutely correct that plenty of human activities, such as SETI, investigations into plagiarism, or encryption, depend on the ability to detect intelligent agency. Where he is wrong is in assuming only one kind of design: for him design equals intelligence and, even though he admitted that such an intelligence may be an advanced extraterrestrial civilization, his preference is for a god, possibly of the Christian variety. The problem is that natural selection, a natural process, also fulfills the complexity-specification criterion, thereby demonstrating that it is possible to have unintelligent design in nature.4

It is reasonable to assume that there may be some who will be swayed by the ID analogy with scientific disciplines like SETI. Therefore, it is the specifics of this analogy that need to be refuted in order to expose its vacuity.

ID as Science

Dembski clearly believes ID will stand up to, and benefit from, a methodology-level comparison with forensics, cryptography, archeology, and SETI. Unfortunately, the analogy is only useful regarding ID if one understands certain assumptions inherent in these disciplines. With this understanding, however, it becomes clear that the comparison of ID with operational science is flawed.

The problems with the analogy can be subtle. What is needed as a foundation is an understanding of what William Dembski calls the Explanatory Filter (EF), which he describes as proceeding in three stages:

At the first stage, the filter determines whether a law can explain the thing in question. Law thrives on replicability, yielding the same result whenever the same antecedent conditions are fulfilled. Clearly, if something can be explained by a law, it better not be attributed to design. Things explainable by a law are therefore eliminated at the first stage of the Explanatory Filter.

Suppose, however, that something we think might be designed cannot be explained by any law. We then proceed to the second stage of the filter. At this stage the filter determines whether the thing in question might not reasonably be expected to occur by chance. What we do is posit a probability distribution, and then find that our observations can reasonably be expected on the basis of that probability distribution. Accordingly, we are warranted attributing the thing in question to chance. And clearly, if something can be explained by reference to chance, it better not be attributed to design. Things explainable by chance are therefore eliminated at the second stage of the Explanatory Filter.

Suppose finally that no law is able to account for the thing in question, and that any plausible probability distribution that might account for it does not render it very likely. Indeed, suppose that any plausible probability distribution that might account for it renders it exceedingly unlikely. In this case we bypass the first two stages of the Explanatory Filter and arrive at the third and final stage. It needs to be stressed that this third and final stage does not automatically yield design — there is still some work to do. Vast improbability only purchases design if, in addition, the thing we are trying to explain is specified.”5

Dembski’s Explanatory Filter (EF) flow chart

To simplify, the EF is an attempt to distinguish between cause by law (necessity), cause by chance, and cause by design; which reduces still further to a choice between undirected natural processes (necessity and/or chance) and some form of intelligent design.

The problems with Dembski’s Explanatory Filter are many and have been documented in various books and websites, especially his probability calculations as applied to biological systems and the utility of ideas he here hints at in the third stage of the Explanatory Filter, e.g. specified complexity. For the purposes of discussing the value of an analogy between ID and SETI (and other sciences), however, we can accept for the moment the legitimacy of the EF. It is my intent to demonstrate that the analogy fails because, first, in ID the distinction drawn between necessity/chance and intelligence is a terminus, it is the goal and the end of the process. In forensics, cryptography, and archeology this distinction is merely an expedient without which the science itself would not take place. Second, although Dembski wishes to paint ID with a coat of science borrowed from these disciplines, the methodological locus between the two is not analogous. And third, the kinds of phenomena ID investigates are not comparable to those dealt with by SETI, forensics, cryptography, and archeology. ID phenomena are inaccessible to science.

Forensic science, cryptography, and archeology (hereafter simply “forensics”) have indeed developed “methods for drawing this distinction,” as Dembski says, but the differentiation they draw is a specific one between undirected natural causes and human intelligent causes. As well, the methods developed have been for detection and elucidation of human intelligent causes in particular, not intelligence in general (assuming that there are other intelligences). This is an important distinction to make because it speaks to the nature of empirical inquiry. These disciplines assume that the phenomenon in question is real, obeys natural laws, and is accessible to scientific methodology. These are assumptions ID proponents cannot claim as fundamental to their own methodology.

The distinctions between necessity/chance and intelligence — natural and intelligent cause — are investigated within the framework of identifiable human effects upon natural processes, and are evaluated on that basis. The salient point is that forensics would not work without an acute understanding of the nature of the intelligence being investigated, or a methodology that investigates the ways in which that intelligence affects the natural world. The assumption of a particular intelligence — human — is built into the process from the beginning. The initial distinction for forensics, then, is not so much between natural causes and intelligent causes as it is between lack of evidence for human causes and evidence for human causes. This is an important difference as it relates to the analogy Dembski applies.

In short, within these disciplines differentiation between necessity/chance and intelligence is a formality. The elimination of chance and necessity leaves a non-controversial “known,” which is human intelligence. This is a mechanism of methodology. It is not a discovery and does not purport to be one. In addition, the locus of actual science in forensics is in the ensuing collection and elucidation of evidence left behind by the same human intelligence. These enterprises are not analogous.


Dealing with the SETI analogy requires a slightly different argument (but one that is equally applicable to the comparison with forensics) because it is obvious that SETI does not assume human intelligence. But, in fact, the SETI project investigates phenomena that occupy a category similar to the phenomena investigated by the afore-mentioned disciplines.

In this analysis, phenomena can be classed in the following fashion:

  1. Explained Phenomena
  2. Unexplained Phenomena (consisting of two subsets):
    1. b1. putative natural phenomena
    2. b2. causally indeterminate phenomena (either natural or non-natural)

Examples relevant to SETI would include, for “A”, instances of known galactic phenomena such as pulsars. An example from the “b1” subset would be along the lines of the transmissions dealt with in the film Contact, i.e. a phenomenon for which examination will hopefully distinguish between undirected and directed (intelligent) cause. It is my argument that implicit in taking action in this case is the assumption that this signal is empirically investigable. That is, it accords with certain preconditions, those being that it is real, it is derived from natural processes, it abides by the physical laws of the universe, and is accessible to current science. The procedure used by SETI is not some unstructured surveillance of the radio spectrum. SETI searches for specific kinds of signals (narrow band) based on specific assumptions about the intelligence that might send them. A statement from the SETI Institute (webpage FAQ) demonstrates this:

There is relatively little background static from galaxies, quasars, and other cosmic noisemakers in the microwave part of the spectrum. This makes faint signals easier to pick out. Additionally, the microwave band contains a naturally-produced emission line, a narrow-band “broadcast”, at 1,420 MHz due to interstellar hydrogen. Every radio astronomer (including extraterrestrial ones) will know about this hydrogen emission. It may serve as a universal “marker” on the radio dial. Consequently, it makes sense to use nearby frequencies for interstellar “hailing” signals.6

It is obvious that this is something quite different from the assumption of intelligence behind an unexplained phenomenon. As with forensics, SETI investigation is a process that employs specific assumptions about the intelligence it investigates. SETI as a science is more than just an attempt to distinguish between necessity/chance and design. Cornell astrophysicist Loren Petrich makes this point clearly,

These reasons are very distinct from Dembski’s Explanatory Filter, which focuses on alleged unexplainability as a natural phenomenon; they are an attempt to predict what an extraterrestrial broadcaster is likely to do, using the fact that they live in the same kind of Universe that we do.7

Examples from the last subset, “b2”, would be any phenomena that at present we are not able to explain. From the perspective of an ID theorist this might be due to the inherent properties of the phenomenon (its “Intelligent Design” etiology). Those of the methodological naturalist persuasion can consider the empirical inaccessibility of phenomena in this subset as owing to a lack of sufficient technological and scientific advancement.

I would assert that SETI does not investigate phenomena derived from the b2 subset. SETI looks for signals based upon experience with analogous natural phenomena. According to SETI scientist Seth Shostak, the search is directed toward finding specific evidence of artificiality, not inexplicability,

If SETI were to announce that we’re not alone because it had detected a signal, it would be on the basis of artificiality. An endless, sinusoidal signal — a dead simple tone — is not complex; it’s artificial. Such a tone just doesn’t seem to be generated by natural astrophysical processes. In addition, and unlike other radio emissions produced by the cosmos, such a signal is devoid of the appendages and inefficiencies nature always seems to add — for example, DNA’s junk and redundancy.8

I submit, then, that while proponents wish to portray “Intelligent Design” theory as analogous to SETI’s investigation of “b1” phenomena, those phenomena that ID attempts to critically consider are actually found within “b2.” In fact, ID finds its epistemological purchase in the very inaccessibility that characterizes “b2” phenomena (ID “discoveries” have been heralded not only as phenomena that science has, as yet, not explained, but as phenomena that science ultimately cannot explain9).

This same argument applies to the attempted analogy with forensic science, cryptography, and archeology. All of these deal with investigation into phenomena that are described in “b1,” that of being unexplained but explainable developments. We can be reasonably confident this is so because they exhibit qualities accessible to science; they are of the natural universe. But phenomena found in “b2” are either presently inaccessible to science or unreasonably attributable to intelligence for lack of evidence. While these qualities obviously allow exploitation by ID proponents they also make the analogy with science inappropriate and self-serving. Comparison of “Intelligent Design” with science is a clear category error.

The Nature of the Designer

The “discovery” of intelligence in “b2” gaps encourages ID proponents to take a pass on attempting to develop any kind of body of work that considers the motives and mechanisms by which an intelligent designer might intervene in the natural world. This endeavor would be directly analogous to the real science with which Dembski and other ID theorists wish “Intelligent Design” to be favorably compared.10 Yet it seems that Dembski would not have us concern ourselves with such inquiries:

What a designer intends or purposes is, to be sure, an interesting question, and one may be able to infer something about a designer’s purposes from the designed objects that a designer produces. Nevertheless, the purposes of a designer lie outside the scope of intelligent design.2

But an inference of “something about a designer’s purposes from the designed objects that a designer produces” is exactly what the methodology of forensics is configured to produce. Additionally this is intimately associated with the methods the designer used which are, in turn, intimately associated with the nature of the designer. These characteristics are not mere empirical by-products of forensics, they are a methodological focus. To compare ID to these disciplines without being able to speak of purposes, methods, and nature of the object of investigation is to ignore the cogent part of the analogy.

To be fair, Dembski tries to rescue the scientific façade: “As a scientific research program, intelligent design investigates the effects of intelligence and not intelligence as such.”2 Here he clearly hopes to hang his hat on the applicability of such notions as “irreducible complexity” and “specified complexity” (his “effects of intelligence”). But these contrivances qualify only as special pleading. Wherever they have been submitted to critical review they have been found to be seriously flawed as useful scientific constructs.11 The utility of these concepts, so far, seems to be as camouflage, an attempt to allow ID to blend in with the scientific environment, while masking its inaccessibility to the scientific method.

To summarize, the analogy of ID to forensics, SETI, and science in general fails for the following reasons:

  1. For ID, differentiation between natural processes and intelligence is an end, for the scientific disciplines it is just a beginning.
  2. In those scientific disciplines it is following this point of departure that most of the science is conducted, with the motives and mechanisms of human (or ET) intelligence being of central concern. These questions are purposefully ignored by ID, leaving it with no analogous locus of scientific methodology.
  3. ID and science address phenomena that are etiologically different. Comparison of ID with science is a category error.

Whether one considers the tactic of analogizing ID with SETI and other sciences a cold calculation or an earnest attempt at dialogue, the goal of the argument is to leave science and scientists in a logical conundrum. As one ID proponent noted,

The ID critic cannot have her cake and eat it too. Either she can allow SETI and archeology into her definition of science — and ID along with them — or she must throw them all out. There is no logical middle ground.12

But an understanding of the specifics of the analogized methodologies reveals that it is actually the proponents of ID who have an uncomfortable decision to make. Either the phenomena that ID theory purports to discover are empirically accessible to science — and therefore derived from natural processes — or they are forever inexplicable, in which case the analogy with scientific methodology fails by definition. Do Intelligent Design proponents leave ID in this epistemological vacuum where it cannot be falsified by the scientific method, or do they allow, and therefore submit to peer review, that their designer must somehow interact with the natural universe in ways that should be detectable, testable, explicable, and eventually expressive of the nature of the designer?

References & Notes
  1. Dembski, William. 2003. “Three Frequently Asked Questions About Intelligent Design.” Textbook hearing, Austin, Texas.
  2. Dembski, William. 2003. “Intelligent Design.”
  3. Pennock, Robert. 1999. Tower of Babel: The Evidence Against the New Creationism. MIT Press, Cambridge, MA, 228-233.
  4. Pigliucci, Massimo. 2002. “Design Yes, Intelligent No.”
  5. Dembski, William. 1996. “The Explanatory Filter: A three-part filter for understanding how to separate and identify cause from intelligent design.” wd_explfilter.htm
  6. SETI Institute Research / Technical Information.
  7. Petrich, Loren. 2003. “Animal and Extraterrestrial Artifacts: Intelligently Designed?” 283
  8. Shostak, Seth. 2005. “SETI and Intelligent Design.”
  9. Behe, Michael J. 1996. Darwin’s Black Box: The Biochemical Challenge to Evolution. Touchstone, New York, NY.
  10. Center for the Renewal of Science and Culture. The Wedge Strategy. features/wedge.html
  11. Irreducible Complexity:
    www. behe.html faqs/behe/review.html Abstracts/Orr_on_Behe_97.html
    Specified Complexity:
    www. young2002a.html design/faqs/nfl/#csi
  12. Alder, J. S. 2001. “Is Intelligent Design Science, and Does it Matter?” 070101.shtml

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