Recently, a creationist blog attributed a particular argument against design to David Hume, so I took a copy of his Dialogues concerning Natural Religion (1779) from the shelf to check. Surprise, surprise: it wasn’t there. But I’m not going to bother to debunk the misattribution; it’s not really interesting. Instead, as long as I have the Dialogues before me, I thought that I would say a word about a particularly strange argument that appears in it, which bears on the age of the world.
If you haven’t read the Dialogues, I should explain that it’s a philosophical work in dialogue form, with three protagonists, Cleanthes, Philo, and Demea. Pamphilus, who narrates the dialogue to his friend Hermippus, comments on “the accurate philosophical turn of Cleanthes,” “the careless skepticism of Philo,” and “the rigid orthodoxy of Demea,” which might lead you to assume that Hume’s views are voiced by Cleanthes. In fact, however, it’s Philo who is generally Hume’s mouthpiece.
Just before the argument I’m interested in, which occurs in part VI of the Dialogues, Philo is in the process of criticizing Cleanthes’s argument from design, which rests on the analogy between the world and a machine. Among his strategies for doing so is to offer what he suggests are equally compelling analogies that fail to support the inference to design: here he broaches the idea that “[t]he world…is an animal, and the Deity is the SOUL of the world, actuating it, and actuated by it” (emphasis in original).
Cleanthes offers two responses. The first is comically inept. Admitting Philo’s point that the world “does, in many circumstances, resemble an animal body,” he adds, “No organs of sense; no seat of thought or reason; no one precise origin of motion and action. In short, it seems to bear a stronger resemblance to a vegetable than an animal.” Perhaps, but the idea that the world is like a vegetable fails to support the inference to design just as much as the idea that the world is like an animal fails to so.
The second is the interesting response. Cleanthes says, “your theory seems to imply the eternity of the world.” Commentators on the Dialogues have struggled to make sense of the supposed implication here. In Reading Hume’s Dialogues (2002), for example, William Lad Sessions protests, “Cleanthes should have asked two prior questions: Why should thinking of the world as (like) an animal body imply its eternity? Why should eternity be more closely connected to an animated world than to an artifactual one?”
Perhaps there isn’t a logical connection here. (After all, animals are mortal, not eternal, so the claim is implausible from the get-go.) Philo attributes the view that the world is like an animal with God as its soul (animus mundi) to “almost all the theists of antiquity,” so perhaps Cleanthes, knowing that those philosophers also generally regarded the world as eternal, is assuming that Philo is proposing the whole package. Perhaps not, though: he claims that the idea of the animus mundi never occurred to him before.
It’s true that Philo is at least inclined to accept the eternity of the world. He doesn’t go so far as to endorse it outright—remember, he’s a “careless” skeptic—but he says, “were I obliged to defend any particular system of this nature (which I never willingly should do), I esteem none more plausible than that which ascribes an eternal, inherent principle of order to the world.” But there’s no indication that he regards the idea that the world is like an animal as supporting the eternity of the world.
Ignoring, then, the question of why Cleanthes thinks that Philo’s suggestion that the world is like an animal implies the eternity of the world, what’s the matter with the eternity of the world? According to Cleanthes, “that is a principle which, I think, can be refuted by the strongest reasons and probabilities.” He adds, “I shall suggest an argument to this purpose, which, I believe, has not been insisted on by any writer.” Before he does so, however, he reviews a similar argument with a distinguished pedigree.
Cleanthes alludes to “[t]hose, who reason from the late origin of arts and sciences.” The argument here, basically, is that there have been innovations in the arts and sciences within the historical record. But if the world were eternal, those innovations would have been arrived at earlier. Ergo, the world is not eternal. Various figures with whom Hume would have been familiar endorsed the argument, including Lucretius and—perhaps unknown to Hume—the towering figure of British thought in his day.
Isaac Newton, according to John Conduitt (who married Newton’s half-niece Catherine Barton, whom readers of Neal Stephenson’s novel The System of the World  will remember vividly), “seemed to be very clearly of opinion that the inhabitants of this earth were of a short date & alledged as one reason for that opinion that all arts as letters long ships printing—needle &c were discovered within the memory of History which could not have happened if the world had been eternal” (spelling and syntax as in original).
But Cleanthes pinpoints a problem with the argument: it presupposes that innovations in the arts and sciences, once attained, are never forgotten. By way of refutation, he appeals to “the nature of human society, which is in continual revolution between ignorance and knowledge, liberty and slavery, riches and poverty,” and cites the Dark Ages as a time in which ancient learning was in danger of perishing. But he thinks that he can improve on the argument, to which I return in part 2.