It's a argument from ignorance, because the proponents of intelligent design argue that if Darwinian scientists cannot explain in precise detail the step-by-step assembly of some irreducibly complex biological mechanism by evolutionary natural selection, then this proves that this biological mechanism was created by a divine intelligent designer.
So, for example, Behe has argued that the bacterial flagellum (the rotating tail of bacteria) is an irreducibly complex biological mechanism, and since no biologist has provided convincing evidence for the step-by-step assembly of bacterial flagella by natural selection in evolutionary history, we must infer that the bacterial flagellum was created by the intelligent designer.
Similarly, Dembski assumes that there are only three kinds of explanatory causes--natural necessity, chance, and design. If we can eliminate natural necessity and chance as likely causes for some event, then we are left with design as the only explanation. If we cannot explain the precise step-by-step path by which the bacterial flagellum arose through purely natural causes or by chance, then we must assume it was designed by some sufficient powerful intelligent agent. Thus, Dembski defines design as the negation of natural regularity and chance, and consequently design has no positive content.
For intelligent design to have some positive content, Behe and Dembski would have to explain exactly where, when, and how a disembodied and sufficiently powerful intelligence designed flagella and attached them to bacteria. Behe and Dembski don't do this, because it better serves their rhetorical strategy of negative reasoning that puts their Darwinian opponents on the defensive. The trick is to demand a standard of proof for Darwinian science that the intelligent design proponents have not themselves met by showing exactly how a disembodied intelligence works in the world.
The argument for intelligent design is also an argument from equivocation in the use of the term "intelligent design." Both Dembski and Behe speak of "intelligent design" without clearly distinguishing human intelligent design from divine intelligent design. We have all observed how the human mind can cause effects that are humanly designed, and from such observable effects, we can infer the existence of human intelligent designers. But insofar as we have never directly observed a disembodied, omniscient, and omnipotent intelligent designer causing effects that are divinely designed, we cannot infer a divine intelligent designer from our common human experience.
Behe is right that from an apparently well-designed mousetrap, we can plausibly infer the existence of a human intelligent designer as its cause, because we have common experience of how mousetraps and other human artifacts are designed by human minds. In the same way, William Paley was right that from a well-designed watch, we can plausibly infer the existence of an intelligent human watchmaker. But from an apparently well-designed organic mechanism (like the bacterial flagellum), we cannot plausibly infer the existence of a divine intelligent designer as its cause, because we have no common experience of how a divine mind designs things for divine purposes.
Dembski has written: "The point of the intelligent design program is to extend design from the realm of human artifacts to the natural sciences." This sophistical rhetorical strategy of equivocation in the use of the term "intelligent design" hides the fact that while detecting the design of human artifacts is a matter of common observation and inference, detecting the design of divine artifacts is not.
At Dembski's website ("Uncommon Descent"), Barry Arrington wrote a post a few years ago responding to these criticisms. Here's the post:
Notice how this illustrates the intelligent design argument from ignorance and equivocation. Notice how Arrington fails to provide any explanation for exactly when, where, and how the intelligent designer creates "the irreducible complexity (IC) or the functionally specific complex information (FSCI) found in living things." So intelligent design theory has no positive explanatory content whatsoever.ID opponents sometimes attempt to dismiss ID theory as an “argument from ignorance.” Their assertion goes something like this:1. ID consists of nothing more than the claim that undirected material forces are insufficient to account for either the irreducible complexity (IC) or the functionally specific complex information (FSCI) found in living things.2. This purely negative assertion is an invalid argument from ignorance. As a matter of logic, they say, it is false to state that our present ignorance concerning how undirected material forces can account for either the IC or the FSCI found in living things (i.e., our “absence of evidence”), means no such evidence exists. In other words, our present ignorance of a material cause of IC and FSCI is not evidence that no such cause exists.This rejoinder to ID fails for at least two reasons. First, ID is not, as its opponents suggest, a purely negative argument that material forces are insufficient to account for IC and FSCI. At its root ID is an abductive conclusion (i.e., inference to best explanation) concerning the data. This conclusion may be stated in summary as follows:1. Living things display IC and FSCI.2. Material forces have never been shown to produce IC and FSCI.3. Intelligent agents routinely produce IC and FSCI.4. Therefore, based on the evidence that we have in front of us, the best explanation for the presence of IC and FSCI in living things is that they are the result of acts of an intelligent agent.The second reason the “argument from ignorance” objection fails is that the naysayers’ assertion that ID depends on an “absence of evidence” is simply false. In fact, ID rests on evidence of absence. In his Introduction to Logic Irving Marmer Copi writes of evidence of absence as follows:In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators. In such circumstances it is perfectly reasonable to take the absence of proof of its occurrence as positive proof of its non-occurrence.How does this apply to the Neo-Darwinian claim that undirected material forces can produce IC and FSCI? Charles Darwin published Origin of Species in 1859. In the 152 years since that time literally tens of thousands of highly qualified investigators have worked feverishly attempting to demonstrate that undirected material forces can produce IC and FSCI. They have failed utterly.Has there been a reasonable investigation by qualified investigators? By any fair measure there has been. Has that 152 year-long investigation shown how undirected material forces can account for IC or FSCI? It has not.Therefore, simple logic dictates that “it is perfectly reasonable to take the absence of proof” that undirected material forces can account for IC and FSCI as “positive proof of its non-occurrence.”As far as I can see, there are two and only two responses the Darwinists can make to this argument:1. The investigation has not been reasonable or reasonably lengthy.2. Give us more time; the answer is just around the corner.Response 1 is obvious rubbish. If thousands of researchers working for over 150 years is not a reasonable search, the term “reasonable search” loses all meaning.Response 2 is just more of the same Darwinist promissory notes we get all the time. How many such notes will go unpaid before we start demanding that the materialists start paying COD?
Arrington claims that ID is not an argument from ignorance, because it is actually "an abductive conclusion (i.e., inference to best explanation) concerning the data." But notice the third step in his abductive inference: "Intelligent agents routinely produce IC and FSCI." He doesn't specify who these "intelligent agents" are. If he's referring to human intelligent agents, then, of course, we can all agree that human intelligent agents routinely produce IC and FSCI. But if he's referring to divine intelligent agents, then he will have to explain to us exactly how "divine intelligent agents routinely produce IC and FSCI."
He doesn't want us to see that, because he wants to hide the movement by equivocation from human intelligent design to divine intelligent design.