Firstly, there is the issue of the completeness of Dembski's triad, which I have talked about below. As a reminder, the challenge is that "chance, design and regularity" don't cover all the bases.

There are two ways in which this is challenge is being presented, and I think it is fair to say that there is a lack of clarity amongst commenters about what the nature of this objection is. The first is to say that there might be "something else" - that chance, design and regularity aren't logically the only options. It was in the context of this approach that I gave the illustration of "detached/semi/terraced" below. To show that this logical challenge is fair, it isn't necessary to show alternative causation that doesn't fit into the triad, it is only necessary to show that alternative causation might logically exist that doesn't fit into these three categories. This hasn't been done, so the logical objection to Dembski's triad hasn't been upheld. At least, thus far!

The other way in which the challenge is presented is to point out that we don't know every regular process, so we can't exclude the possibility that there is a regular process that we don't know about which has been overlooked as an explanation.

However, "unknown regularity" is still regularity. Dembski allows for this, and accepts that a design inference might be provisional, because we don't necessarily know all natural processes. Similarly, he points out that it is possible that some things may be tagged as "chance" when in actual fact they require "design" (he gives examples).

However, he points out that there are certain phenomena that natural processes can't be shown to explain. Setting aside the presumption that evolution is a natural process, can it be shown in any other sphere that complex specified information can appear through the application of laws? Or that a natural process can produce an irreducibly complex object?

Next, I set a challenge for opponents of ID. This was: come up with a basis for identifying design, and then apply it to biological systems to show that they haven't been designed. Mark Frank, who disturbingly chose the same blog template as me (a specified event of low probability, but not below the universal probability boundary!), has provided the most thought out response to this challenge.

The most interesting point he makes - and I hope I'm presenting his argument fairly - is that when we don't know the probability that there is a designer, it isn't possible to determine the relative probabilities of the chance inference and the design inference. I wonder if he has stumbled upon the key question that underlies the whole debate between evolutionism and ID.

Let's assume that a phenomenon is a specified event of low probability - say the probability of it happening is one in 10

^{100}. The chance hypothesis doesn't look great. But supposing the probability of there being a designer is only 1 in 10

^{400}. Then the chance hypothesis looks a lot better.

Dembski presents the idea of the universal probability boundary. If a specified event is of a probability less than one in 10

^{150}, then the universe doesn't have the probabilistic resources for the event to occur. You have to construct a "multiverse" - an arbitrarily large number of other universes, none of which are verifiable - for a naturalistic explanation to be plausible in even one universe. Hypothesising an arbitrarily large number of other universes is hardly consistent with Occam's Razor! However, if the probability that there is a designer in this universe is also below the universal probability boundary, then you are kind of stuck with that conclusion, I guess.

So how do you determine the probability of there being a designer for biological systems? We could do it democratically - and conclude that if 30% of the world's population think that there is a transcendent "other" who brought about the world, then the odds are 0.3. On this basis, if even one person in the world believes in such a being, then the odds are no worse than 1 in 10

^{10}. We could weigh up the evidence for ourselves, and come to our own conclusion. The Bible argues that people know that there is a God, and they repress this knowledge. There aren't many people, I suspect, who behave as though there definitely is no transcendent other.

Although some of the opposition to ID comes from people who wish to exclude the possibility that a transcendent other might intervene in the universe, I suspect that a scientist would be happy to assign a finite (but small, if necessary) probability to the existence of a designer, which would allow a comparison between the chance inference and the design inference to be carried out.

Mark has said more that I may come back to at some stage, time permitting.