Sarah Broadie's second Whitehead lecture was an exploration of Aristotle's conviction that heavenly spheres are divine, and of the resulting dualism, and tensions, in his philosophy of nature.
Broadie began by recounting Aristotle's cave argument, as reported by Cicero in De Natura Deorum II.95:
“If there were men who had always lived underground in fine and well-lit houses which had been adorned with statues and paintings, and equipped with all the things which those who are considered well-to-do possess in abundance, who had, however, never come forth into the upper world, but had learned by fame and hearsay of the existence of certain divine powers and natures, and had then at some time, through the jaws of the earth being opened, been able to come forth from those hidden regions, and to pass into these parts which we inhabit,—when they had suddenly obtained a sight of the land and seas and sky, and had marked the vastness of the clouds, and the force of the winds, and had beheld the sun, and had marked not only its size and beauty, but also its power, since by diffusing light over the whole sky it caused day,—and when, again, after night had overshadowed the earth, they then perceived the whole sky studded and adorned with stars, and the change in the light of the moon as it alternately waxed and waned, and the rising and setting of all these bodies, and the fixity and unchangeableness of their courses through all eternity,—when they saw those things, they would assuredly believe both that the gods existed and that these mighty works proceeded from them (haec tanta opera deorum esse arbitrarentur).”The passage, Broadie said, gives an elegant version of the Argument from Design. It is not unlike an Ideal Observer argument, as the hypothetical circumstances of the cave dwellers are constructed in such a way as to eliminate circumstances that could hinder their arriving at a sound judgment, e.g.
Q. Why doesn't everyone agree that the gods exist? A. Because we take for granted the evidence of their existence, from familiarity.The passage, if it truly does express Aristotle's view (as it was taken from a dialogue, On Philosophy), would however simply be one among many examples of what seems to have been constant feature of Aristotle's thought, viz. he is not disposed to explain away the gods or belief in gods.
Q. Isn't it only the humble outlook of primitive peoples that leads them to believe in gods, when they see impressive phenomena in nature? A. No, even if people lived all their lives in luxurious circumstances, they would still be so impressed by nature as to be disposed to believe in gods.
Aristotle was a theist. However, his theism is not to be located principally in his famous arguments for a Prime Mover: these arguments are not intended as bits of theology but rather as basic explanations in a philosophy of nature. Rather, his theism is bound up with his belief that it is physically necessary that the heavens are in eternal, rotational motion. Yet this belief leads to a certain dualism and tension in his theory of the universe.
Unlike Plato, Aristotle holds that the universe is eternal, going back into the past, and not only going forward into the future. For Plato, eternity into the future was guaranteed by each thing's having a kind of 'stamp' of its divine origin, an immaterial pattern, which, when we grasp it, leads us back to a consideration of the original, divine Mind. But for Aristotle, because the universe is eternal stretching back into the past, every generation of mortal beings must have come about by natural processes. Admittedly, these processes are end-directed and craft-like, but the ends are non-mental, and the 'craft' never involves control by external agency. Explanation by appeal to natural processes is internal to the things explained and "naturalistic through and through". Thus, for Aristotle, in the sublunary world the 'craft of God', so important for Plato, is "completely out of the picture." Thus, we cannot survey the realm of generation and passing away and see in it the stampt of the same deity who made the heavens. The evidence for theism, and its chief object, becomes the heavens alone.
Note that it is not appropriate to regard Aristotle's philosophy of nature as part of some general project of 'demystification', and then wonder why he didn't extend the same outlook to the heavenly spheres. Aristotle did not develop his philosophy of nature as part of such a project; and he thought the universe could not be explained apart from the view that the movement of the heavenly spheres is eternal and physically necessary.
The result is that one finds in Aristotle a radical disparity between the sublunary and the celestial, which cannot be bridged in the manner of Plato, by tracing both back to a common cause.
Not that Aristotle does not try to bridge this gap through various devices:
- he reaffirms Plato's dictum that mortal animals participate in immortality through reproduction;
- he holds that processes of mortal generation depend upon regularities in celestial motion;
- he emphasizes that every science, even one dealing with the sublunary realm, must be general and appeal to universals;
- his view of human investigation is such that this also binds the sublunary to the celestial, as human beings have always existed, and have always wondered at the heavens;
- the cycles of the four sublunary elements, he holds, mimic the rotational movement of the heavens;
- indeed, in Met. XII he refers to both domains as including "perceptible substances", which unifies them in constrast with the non-perceptible.
- he employs the same notion of natural locomotion to explain both the natural motion of the four sublunary elements and the motion of the celestial spheres.
The theory of natural motion of the elements is that each element moves through space in a way natural to itself, towards its natural place, and that it moves away from its natural place only because of the continuous application to it of external force. Aristotle wishes to apply this theory to the celestial spheres: a necessarily eternal motion could not be enforced from without; therefore it must be the manifestation of the natural motion of sui generis celestial stuff, the 'aither'.
However, the consequence is that this 5th element has no role to play vis-a-vis the other four. It cannot enter into sublunary processes. And, although the 5th element has a place (it surrounds the sublunary), it does not really share the same space as the other four elements, because it is not as though there is some common space, to which in principle they might all go.
So the dualism remains. Aristotle seems content with it, because of his conviction of the eternal, physically necessary motion of the heavens.
But one might wonder in the end: Why wasn't Aristotle tempted to extend to celestial stuff the same outlook as he applied in the sublunary, which apparently "takes the craft of God completely out of the picture"? Why didn't he say that it is as absurd to view the motions of the heavens as the work of divinities, as to view the motion of earth, air, fire, and water as the work of 'minds' implicit in them?
But Aristotle regarded it as absurd to postulate minds to explain the motions of the four sublunary elements, because they are formless. Yet the celestial spheres are not formless. They maintain forever a perfect spherical shape. But he would think that this could not be achieved by a mere body or element. (Compare what it takes for the body of a terrestial animal to maintain a certain shape, on Aristotelian grounds, and one might begin to see Aristotle's way of looking at this.)