by Michael Lopresto



It's commonplace today to think that the argument for design, with the aim of rationally establishing the existence of God, was refuted by Darwin in 1859, with the publication of The Origin of Species. This view is not only held by evolutionary biologists such as Richard Dawkins, but also top-notch philosophers such, John Mackie and Elliot Sober (and to some extent Arif Ahmed). Against this commonplace, the philosophers Simon Blackburn and Graham Oppy object that on logical grounds, David Hume (1711 – 1776), the great philosopher of the Scottish Enlightenment, dealt the argument for design its fatal blow. This was done in Hume's magnificent and delightful Dialogues Concerning Natural Religion, published posthumously in 1779, but written over the middle years of the century.

So, what exactly is the argument for design? It's an argument intended to demonstrate the existence of God—and here we're concerned only with the Judeo-Christian-Islamic God who's defined as being omnipotent, omniscient and perfectly good—from the observation that there is apparent design in the world. The term “observation” is crucial here; the argument's not intended to proceed purely from the armchair like the ontological argument is, for instance, which seeks to deduce the existence of God from the mere concept GOD (the being which no greater can be conceived), and the ancillary premise that existence is a perfection. Indeed, the world could be any way at all—it could contain much more gratuitous evil, say, and the ontological argument wouldn't claim to be any less valid. This is because the ontological argument is purely a priori: it's an argument that proceeds independently of experience (observation) of the world.

The argument for design isn't like this. Rather, it's an a posteriori argument, deploying contingent truths about apparent design garnered from experience. Indeed, the argument can't even be deductively valid, as there is no valid inference from apparent design to intentional design. So the argument needs to be empirical in nature, namely, an inference to the best explanation (explanatory inference for short), which is an empirical inference par excellence (I think it's also probably the central inference of philosophy, but that's another story). So the argument for design, for the existence of God, is that the best explanation (philosophical premise) of apparent design (empirical premise) in nature is that nature was intentionally designed by God.

Perhaps the most famous presentation of this line of reasoning was put forward by the natural theologian William Paley in his 1802 Natural Theology (quoted in the SEP), now (perhaps infamously) known as the “watchmaker's analogy”:

In crossing a heath, suppose I pitched my foot against a stone and were asked how the stone came to be there, I might possibly answer that for anything I knew to the contrary it had lain there forever; nor would it, perhaps, be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place. I should hardly think of the answer which I had before given, that for anything I knew the watch might have always been there. Yet why should not this answer serve for the watch as well as for the stone? Why is it not as admissible in the second case as in the first? For this reason, and for no other, namely, that when we come to inspect the watch, we perceive—what we could not discover in the stone—that its several parts are framed and put together for a purpose … [The requisite] mechanism being observed … the inference we think is inevitable, that the watch must have had a maker. … Every observation which was made in our first chapter concerning the watch may be repeated with strict propriety concerning the eye, concerning animals, concerning plants, concerning, indeed, all the organized parts of the works of nature. … [T]he eye … would be alone sufficient to support the conclusion which we draw from it, as to the necessity of an intelligent Creator. …

It may seem that Paley is cheating here, for the reason that we perceive intentionally designed purposiveness in the watch is that we already know, from culture and experience, that watches are intentionally designed for telling us the time. But we can grant this for the sake of argument; after all, we do know from hindsight that biological complexity requires special explanation, namely the theory of natural selection, but it's my contention in this essay that even before 1859, one could be an intellectually fulfilled atheist. Indeed, that Hume gave better explanations for apparent design than by appealing to an intentional designer.

Del Ratzsch in the Stanford Encyclopedia of Philosophy puts the Paley design argument, the watchmaker analogy, like this:

Entity e within nature (or the cosmos, or nature itself) is like specified human artifact a (e.g., a machine) in relevant respects R. a has R precisely because it is a product of deliberate design by intelligent human agency. Like effects typically have like causes (or like explanations, like existence requirements, etc.)

Therefore:

C. It is (highly) probable that e has R precisely because it too is a product of deliberate design by intelligent, relevantly human-like agency.

This is the precise sort of argument that Hume was criticising decades before Paley. In Hume's Dialogues, there are three central characters, Demea, the rationalist putting forward a priori arguments (à la Leibniz) who was emphasising the perfection and infinitude and so forth of God. Cleanthes represents the empiricist putting forward a posteriori arguments (à la Locke), and who puts forward a similar Paley-style argument to the one presented here. And finally there's Philo, the religious sceptic, who represents Hume himself. One of the masterstrokes of the Dialogues is that through some guidance of Philo, Hume gets the believers to turn against each other. The rationalist Demea is little better than an atheist because he can barely say anything at all about his mysterious and incomprehensible God. The empiricist Cleanthes, putting forward his argument for design, is little better than an atheist, with his rampant anthropomorphism, bringing God down to the level of a human. As Simon Blackburn says perspicaciously, in the spirit of Hume, “The two wings of theology, one making God immanent, something to be understood as analogous to ourselves, and one making him transcendent, beyond spatio-temporal physical understanding, simply cannot be reconciled. The believer has to oscillate incoherently, averting attention from first one and then the other.”

To my mind, rampant anthropomorphism is reason enough to reject the argument for design, but alas, Hume has more insightful things to say. This also leads to the issue I began this essay with: Dawkins, Mackie and Sober each think that Darwin offered the best explanation for apparent design that didn't appeal to an intentional designer. Obviously there's a sense in which Darwin did, since Darwin's explanation is true. But there are several important points that have been missed in this commonplace inference: (i) design arguments of the 18th and 19th centuries sought to establish the existence of a single perfect and all-powerful Designer God; and Hume showed that such arguments are much more compatible with multiple imperfect deities; (ii) said arguments often didn't appeal to biology at all, but to things like astronomy; (iii) one could be an intellectually fulfilled atheist before 1859; (iv) we are now in a similar position to Hume with respect to so-called fine-tuning of the cosmos, which seems to be rather friendly to the existence of intelligent life.

(i) Hume showed that design arguments by absolutely no means necessitated a single perfect and all-powerful Designer God. Complex human artifacts aren't designed by a single human, but are designed by committees and are incrementally improved upon over generations. In fact, our world being created by a committee who couldn't agree upon things not only fits the argument better than the monotheistic God conclusion, but it also fits the empirical data much better, as it explains the abject imperfection and waste we find in the world. Imperfection and waste being everything from children being born with horrific congenital conditions to loss of animals in bushfires.

(ii) One major problem with saying that Darwin refuted the argument for design is that creationists can just start banging on about the fine-tuning of cosmological constants. Natural selection explains apparent design in biology, but it doesn't explain cosmological fine-tuning. Hume's suggestion that a committee who couldn't agree on their design being a much better explanation than a single perfect and all-powerful God equally holds for fine-tuning. Hume's objection has much more generality than Darwin's. Hume also put forward other hypotheses to explain apparent design, like the world having an “eternal inherent principle of order” (Part VI of the Dialogues).

(iii) and (iv) have much in common. Before 1859, one could have been an intellectually fulfilled atheist because there were actual and possible explanations for apparent design that didn't appeal to an intentional designer. The fact that more people were convinced by Darwin than by Hume is a purely sociological phenomenon. Hume addressed the logic of design arguments, an impressive feat in itself, but Darwin gave us concrete answers. How is it possible to be an intellectually fulfilled atheist today in the face of apparent fine-tuning crying out for explanation? One answer could just be induction. A naturalistic, non-intentional explanation was given in the case of biological complexity, for which it had hitherto been argued required an intentional designer (a perfect and all-powerful one at that), so it's likely that the same will happen for fine-tuning. However, it seems to me that the more philosophically grounded answer is that Hume taught us that you can't validly infer the existence of a perfect and all-powerful Designer God from actual intentional design (granted for the sake of argument) in the universe—let alone have it be the best explanation for apparent design.