How Not to Detect Design*
A review of William A. Dembski’s The Design Inference -- Eliminating Chance Through Small
Probabilities. Cambridge: Cambridge University Press. 1998. xvii + 243 pg. ISBN 0-521-62387-1.
Branden Fitelson, Christopher Stephens, Elliott Sober†‡
Department of Philosophy, University of Wisconsin, Madison
As every philosopher knows, “the design argument” concludes that God exists from
premisses that cite the adaptive complexity of organisms or the lawfulness and orderliness of the
whole universe. Since 1859, it has formed the intellectual heart of creationist opposition to the
Darwinian hypothesis that organisms evolved their adaptive features by the mindless process of
natural selection. Although the design argument developed as a defense of theism, the logic of
the argument in fact encompasses a larger set of issues. William Paley saw clearly that we
sometimes have an excellent reason to postulate the existence of an intelligent designer. If we
find a watch on the heath, we reasonably infer that it was produced by an intelligent watchmaker.
This design argument makes perfect sense. Why is it any different to claim that the eye was
produced by an intelligent designer? Both critics and defenders of the design argument need to
understand what the ground rules are for inferring that an intelligent designer is the unseen cause
of an observed effect.
Dembski’s book is an attempt to clarify these ground rules. He proposes a procedure for
detecting design and discusses how it applies to a number of mundane and nontheological
examples, which more or less resemble Paley’s watch. Although the book takes no stand on
whether creationism is more or less plausible than evolutionary theory, Dembski’s epistemology
can be evaluated without knowing how he thinks it bears on this highly charged topic. In what
follows, we will show that Dembski’s account of design inference is deeply flawed. Sometimes he
is too hard on hypotheses of intelligent design; at other times he is too lenient. Neither