I admit to a certain affinity for logic-based arguments. There is a purity to logic, and the promise of an objective outcome, an unambiguous conclusion. Evidence is messy and always contingent; but logic is either valid or invalid; arguments are either sound or they are unsound.

This is partly why one of my favorite pseudosciences to stalk is creationism/intelligent design (ID). It is a treasure trove of logical fallacies. Countering all of the invalid arguments put forth by proponents of creationism/ID constitutes a thorough and in depth lesson in logic.

Today’s lesson regards the argument from ignorance. This fallacy describes an argument that bases a positive claim on the absence of evidence, or what is not known. If one sees an unidentified blob of light in the sky and concludes from the inability to identify the light that it is an alien spacecraft, that is an argument from ignorance.

Intelligent design is one giant argument from ignorance. The basic argument is that certain biological structures and pathways cannot be explained through naturalistic mechanisms, therefore they must have been designed by some intelligent agent. Of course the premise to this argument is not true because it is based upon another logical fallacy – the confusion of currently unexplained with unexplainable. The structures and pathways (bacterial flagella, the clotting cascade) that were pointed to as unexplainable by IDers have now been largely explained. Since we don’t and never will know everything, there will always be currently unexplained phenomena in biology, but since steady progress is constantly being made it is not valid to argue that currently unexplained phenomena are unexplained because they are unexplainable.

But that aside, even if we grant that there are unknowns in biology, it is still not logically valid to conclude from this that any particular explanation must be true. What IDers argue is that because we cannot provide an adequate evolutionary (or any naturalistic) explanation for the complexity we see in life, it must have been deliberately designed. This is an argument from ignorance.

The ID community, of course, is uncomfortable with the notion that their entire field is teetering atop a logical fallacy, so they are desperately trying to defuse this criticism. In this recent blog post over at the Discovery Institute Robert Crowther tries to dismiss the argument from ignorance criticism with typical misdirection. He confuses this with the retort often made by ID critics of “who designed the designer,” not recognizing that this is a distinct criticism. He also uses a bit of ad hominem by saying the argument from ignorance is invoked so frequently by scientists that it is a symptom of OCD. I’ll give him the benefit of the doubt by writing this off as a poor literary device rather than a serious criticism.

The only real argument against the argument from ignorance criticism of ID that I could find in the post was a quote from another post by Crandaddy at Uncommon Descent who wrote: “Neither Pim nor any other ID critic I have encountered has ever given an adequate explanation of just what evidence for a designer would look like, or if they have, I have yet to see it.”

The inability to articulate what form positive evidence for a designer would take is not a valid argument against the argument from ignorance criticism of ID, but rather reflects the weakness of ID itself. It reflects the fact that IDers have not proposed a scientifically testable hypothesis, and this relates to their refusal to characterize the designer.

In other words, IDers are trying to argue that we can look at nature and conclude it was purposefully designed without knowing anything about the designer. But this an inherently flawed approach – specifically because it can make no predictions about what positive evidence should exist and therefore necessarily relies upon the argument from ignorance.

The logical problems start with the formulation of the premises – that there is “design” in nature. To an extent this is true – biological organisms have complexity that is designed to serve a purpose for the survival and reproduction of the organism. But IDers are using the term “design” in an artificially narrow sense, as if design automatically implies intelligence or deliberateness. But it doesn’t. That is, in fact, the very question at hand – what is responsible for the design. IDers want to short circuit any process of discovering scientifically what caused the complexity of life by equating up front design with intelligence.

Science has a pretty good answer – evolution. Evolution can design organisms, through variation and natural selection. More importantly, we can ask – what would something designed by evolution look like? We can investigate the mechanisms of evolution and make predictions about how that would affect what we see in living nature. (So far all the predictions made by evolutionary theory have been confirmed, and multiple opportunities to falsify evolution have not done so.)

The inherent problem with ID is that it does not make any predictions. IDers profess to know nothing of the designer or the mechanisms of creation. What would life look like if it were designed? Like anything the designer wants, I suppose. So whatever we see in nature is compatible with ID, therefore ID makes no predictions, therefore it is not a scientific theory.

And (here is the ultimate point) there can therefore be no positive evidence for ID. ID is therefore doomed to rest upon the absence of evidence for other imagined alternatives (and again, for emphasis, it fails in this respect as well) – the argument from ignorance.

But IDers, as the Crandaddy statement demonstrates, have fallen into the trap of thinking that if something is True (with a capital “T”) then it must be possible for there to be positive evidence for it. This is not a valid position, however. Science is not about what is True but about what we can know. Things can be True but unknowable and therefore outside the methods of science. It may be the ultimate truth of reality that an omnipotent creator designed the universe to look exactly as if it evolved naturally – but we’ll never know, as this is not a scientific notion.

If it is not possible to have positive evidence (and this seems to be what Crandaddy is implying by saying that ID critics cannot say what such evidence for design would be) then what? What I have argued above is that therefore the hypothesis is not falsifiable and therefore not science. What Crowther and other IDers argue, however, is that therefore the absence of evidence for alternatives (again the argument from ignorance) is acceptable.

In other words, what the ID community has done is put forth a flawed hypothesis that is not scientific because it does not allow for positive evidence, then challenge the scientific community to explain how there could be positive evidence for their flawed hypothesis or be forced to accept the argument from ignorance as legitimate. That’s quite an intellectual shell-game, but then creationists and IDers are very good at that.