But if all the parts of the universe have been so ordered that they could not have been better adapted for use, or more beautiful as regards appearance, let us see whether they are the work of chance, or whether their arrangement is one in which they could not possibly have been combined except by the guidance of consciousness and the divine providence. If, then, the things achieved by nature are more excellent than those achieved by art, and if art produces nothing without making use of intelligence, nature also ought not to be considered destitute of intelligence. If at the sight of a statue or painted picture you know that art has been employed, and from the distant view of the course of a ship feel sure that it is made to move by art and intelligence, and if you understand on looking at a horologe, whether one marked out with lines, or working by means of water, that the hours are indicated by art and not by chance, with what possible consistency can you suppose that the universe which contains these same products of art, and their constructors, and all things, is destitute of forethought and intelligence? Why, if any one were to carry into Scythia or Britain the globe which our friend Posidonius has lately constructed, each one of the revolutions of which brings about the same movement in the sun and moon and five wandering stars as is brought about each day and night in the heavens, no one in those barbarous countries would doubt that that globe was the work of intelligence.--Cicero, On the Nature of the Gods.
There are three explicit mentions of Posidonius, the great Stoic philosopher, in Cicero's dialogue, On the Nature of the Gods. (I have used a slightly dated translation.) The first one is in Cicero's own voice, when he includes Posidonius among his "teachers.' The second is the passage above, which was celebrated in eighteenth century renditions of the design argument. Let's call it the "Posidonian argument." It shows up, for example, in Derham's very popular and influential Physico and Astro-Theology (originally 1714, I think). But it is also familiar in the seventeenth century. (See Cumberland's use of it here.) It reminds us that Paley's famous argument has a long and known pre-history. Hume alludes to a version of the argument in the Enquiry and discusses it more at length in his Dialogues (here and here) and may have even enjoyed transforming Cicero's "Britain" into a desert island. Even so, Hume's treatment does not explicitly mention Posidonius or his portable planetarium (not unlike the now famous Antikythera mechanism [this post was inspired by Jo Marchant's entertaining book about the mechanism!]) In an age in which the motions of the heavenly bodies define time, a planetarium just is a watch.
There is no doubt that Hume was familiar with Cicero's On the Nature of the Gods, which (as many have noted) is an important model for his own posthumous Dialogues. Hume quotes De Natura Deorum in the second Enquiry. Moreover, Hume ranks Cicero together with Lucian as the least superstitious Ancient author. Given that Hume desired to be remembered alongside Lucian, whom he publicly read on his deathbed (see for analysis here), and did so knowing that his own Dialogues were (despite Adam Smith's unwillingness to publish them on his behalf) forthcoming.
Now, in the dedication to Hume's Four Dissertations, which included such crucial texts as "The Natural History of Religion" and "Of The Standard of Taste," Hume describes his political-theological ideal, "true liberty," as follows:
Another instance of true liberty, of which antient times can alone afford us an example, is the liberty of thought, which engaged men of letters, however different in their abstract opinions, to maintain a mutual friendship and regard; and never to quarrel about principles, while they agreed in inclinations and manners. Science was often the subject of disputation, never of animosity. Cicero, an academic, addressed his philosophical treatises, sometimes to Brutus, a stoic; sometimes to Atticus, an epicurean.
Note, first, that in Hume's view "true liberty" has only existed in Ancient times. At least this is so prior to his dedication to his cousin John Home (see the paragraph before the one just quoted). So, Hume signals that he and his intimates may be the first to have recovered such true liberty. In Smith's obituary of Hume, Smith captured this as follows: "Mr. Hume’s magnanimity and firmness were such, that his most affectionate friends knew, that they hazarded nothing in talking or writing to him as to a dying man, and that so far from being hurt by this frankness, he was rather pleased and flattered by it." Given that Hume's friends knew of Hume's opposition to the immortality of the soul, we can infer that they did not recycle fables about the afterlife with him.
Second, Hume means that the introduction of Christianity has made genuine free-thinking impossible (a similar line of argument is developed in the first Enquiry, chapter 11: "This pertinacious bigotry, of which you complain, as so fatal to philosophy, is really her offspring, who, after allying with superstition, separates himself entirely from the interest of his parent, and becomes her most inveterate enemy and persecutor.") It is a bit ambiguous if Hume is making a political point about the political intolerance of Christianity, or (more likely) a moral-psychological point--Christianity is (in his terminology) a disease of the mind that makes it impossible to avoid quarreling about fundamental matters. Given that Hume was undoubtedly familiar with lots of gentle, indulgent Christians I assume he means that genuine shared intellectual enquiry about first principles is impossible with Christians (who can, say, not go against articles of faith, etc.). In his Dialogues Hume dramatizes this by the rupture with Demea, who eventually leaves the conversation.
Third, Hume's focus is on the scrutiny of "abstract opinions," "principles," and "science." That is to say not unlike Spinoza, Hume (no friend of the monkish virtues) here focuses not so much on Christian virtue, but on the impact of Christian metaphysics and ontology. Fourth, Hume explicitly treats Cicero's attitude toward science and metaphysics as an exemplar of such "true liberty."
Okay, let's turn to Adam Smith, who writes in his posthumously published work, Essays on Philosophical Subjects:
As soon as the Universe was regarded as a complete machine, as a coherent system, governed by general laws, and directed to general ends, viz. its own preservation and prosperity, and that of all the species that are in it; the resemblance which it evidently bore to those machines which are produced by human art, necessarily impressed those sages with a belief, that in the original formation of the world there must have been employed an art resembling the human art, but as much superior to it, as the world is superior to the machines which that art produces. The unity of the system, which, according to this ancient philosophy, is most perfect, suggested the idea of the unity of that principle, by whose art it was formed; and thus, as ignorance begot superstition, science gave birth to the first theism that arose among those nations, who were not enlightened by divine Revelation. "The History of Astronomy." (HA; emphasis added)
First, I hope readers will agree that the emphasized part is a clear echo of the Posidonian argument. There is surprisingly little other evidence that Smith is engaging with Cicero's De Natura Deorum, but see here. (Many of the most learned commentators think Smith is entirely unaware of Posidonius's science, because of this paragraph.) Second, Smith uses it for his main historical claim that theism is a consequence of the scientific (or natural philosophic) mindset completely distinct from the introduction of Christianity. This is a subtle correction to Hume's argument in the Natural History of Religion, where in his treatment of Greek natural philosophy, Hume had claimed that "it was pretty late too before these be thought themselves of having recourse to a mind or supreme intelligence, as the first cause of all." So, while Hume treats theism as a kind of alien infection of even Greek science, Smith treats it as natural consequence of scientific mind-set. (Cf. Hume's treatment of Thales with Smith's treatment of Thales' astronomy!) Third, there is a complication related to this second point that I motivate with a brief aside: for Smith *all scientific systems* are to be understood as machines with an internal development related to problem-solving capacity and (even revolutions between systems): "A system is an imaginary machine invented to connect together in the fancy those different movements and effects which are already in reality performed. The machines that are first invented to perform any particular movement are always the most complex, and succeeding artists generally discover that, with fewer wheels, with fewer principles of motion, than had originally been employed, the same effects may be more easily produced." (HA; for more on this see here.) So, Smith self-consciously models his analysis about the way science operates on the same analogy that gets exploited in the Posidonian argument!
Fourth, this raises the question how Smith understands the force of the Posidonian argument. By this I do not mean to what degree Smith believes in final causes or a Providential God (an issues that vexes Smith scholarship obsesses with the workings of invisible bodyparts--as I have pointed out this tends to ignore more significance issues about Smith's theology). Rather, how to understand the following analogy: "as ignorance begot superstition, science gave birth to the first theism." It is very tempting to that that in so far science is contrasted with ignorance, theism is contrasted with superstition. Yet, the larger paragraph from which the analogy is quoted is rhetorically more complex. For earlier in the same paragraph Smith writes:
Their ignorance, and confusion of thought, necessarily gave birth to that pusillanimous superstition, which ascribes almost every unexpected event, to the arbitrary will of some designing, though invisible beings, who produced it for some private and particular purpose. The idea of an universal mind, of a God of all, who originally formed the whole, and who governs the whole by general laws, directed to the conservation and prosperity of the whole, without regard to that of any private individual, was a notion to which they were utterly strangers. (HA; emphasis added)
It seems that Smith makes a distinction between a variety of superstition, and one of the scales seems to go from pusillanimous superstition to magnanimous superstition. And I think a very natural reading of the quoted passage is that the second, more Stoic, providential God is a kind of magnanimous superstition. This second species of superstition is the one associated with eighteenth century, Newtonian natural religion familiar to us from Hume's character in his Dialogues, Cleanthes. Hume and Smith were familiar with the writings of the towering Scottish Newtonian, Colin MacLaurin, who seems to have been the partial model for Cleanthes. If this is right then we can understand why the ever cautious Smith (modeling his own behavior on Hume) decided to leave this work for posthumous publication.
As an aside, this also suggests that for Smith magnanimity can come in a superstitious kind (the Stoics, but also Caesar) and the non-superstituous kind (Hume, see above), among other options, perhaps.
Finally, if the Posidinian argument is an instance of magnanimous superstition and Smith models his treatment of science on it, then Smith is treating science as a species of magnanimous superstition! This is not as crazy as it sounds. For, in a companion piece, "The History of Ancient Physics," Smith explicitly describes the very first instances of science as instances of "vulgar superstition" (the whole paragraph concludes with: "the lowest and most pusillanimous superstition supplied the place of natural philosophy.") The development of science itself is then understood as a refining away (to use an eighteenth century metaphor) of superstitious elements. But given the length of this post, I shall leave open to what degree Smith thought that science -- which he understood as essentially a passion-driven social enterprise -- could ever be free from superstition
PS. This is the third mention of Posidonius in Cicero's De Natura Deorum:
Undoubtedly, then, there is more truth in what our common friend Posidonius urged in his fifth book on the nature of the gods, that Epicurus has no belief in their existence, and that what he said on the subject of the immortal gods he said for the sake of deprecating odium. Cicero. (Cf. Smith on the Pythagoreans or Ancient astronomers more generally.)