According to William Dembski, design can be detected or inferred by using what he terms an “explanatory filter.” This “filter” checks for signs of contingency, complexity, and specificity, while filtering out the background noise of mere chance and necessity. If an event or an object exhibits all three of the enumerated factors — contingency, complexity, and specificity — it can be identified as the result of an intelligent cause (as contrasted with a nonintelligent material cause). Each of the three factors is necessary to indicate design, but none is, by itself, sufficient. All three must be present. If all three factors are present, however, their presence is both a necessary indicator of design and a sufficient one.
But what do these terms mean?
For Dembski, an event or an object is to be considered contingent if it cannot be explained as the result of natural law — that is, if it cannot be accounted for by automatic processes. As an example, he offers a crystal of salt. Salt crystals can be fully explained on the basis of chemical processes that function according to chemical laws. Thus, they are not to be considered contingent in his sense of the term. By contrast, a complex table setting of silverware cannot be explained on the basis of natural laws and automatic function. So, instinctively and naturally, when we see such a table setting we immediately recognize that it was laid out by an intelligent agent (e.g., by the butler, or by virtually anybody who knows more about table settings than I have yet managed to master). Of course, natural laws act on contingent events and contingent objects — e.g., gravity affects place settings on a dining table, as well as outfielders throwing in to a catcher in the hope of putting out a runner approaching home plate, and heat causes the snowman that I’ve built to melt and to droop — but natural laws do not and cannot exhaustively account for them.
Complexity is a function of probability. The greater its complexity, the less probable it is that a given event or object arose by chance — which is to say, without intelligent causation. But, as noted above, complexity alone is insufficient to establish the influence of an intelligent agent. As Dembski points out,
Complexity by itself isn’t enough to eliminate chance and indicated design. If I flip a coin 1,000 times, I’ll participate in a highly complex (or what amounts to the same thing, highly improbable) event. Indeed, the sequence I end up flipping will be one in a trillion, trillion, trillion, . . . where the ellipsis needs twenty-two more “trillions.” This sequence of coin tosses won’t, however, trigger a design inference. Though complex, this sequence won’t exhibit a suitable pattern to detect design.*
Thus, while both contingency and complexity are required for the inference of design to kick in, neither contingency nor complexity nor even a combination of the two is sufficient to fully justify such an inference.
* See William Dembski, “Science and Design,” First Things (1 October 1998). Also available at https://www.discovery.org/a/62/.
To be continued.