Aristotelian Cosmology: Heavenly Bodies and Earthly Bodies

Aristotle conceived of a distinction between the constitution of bodies in the heavenly and earthly realms, an idea echoed by St. Paul’s distinction between celestial, heavenly or “spiritual” bodies and earthly “physical” bodies: “All bodies are not the same…there are celestial bodies and there are earthly bodies. The glory of the celestial is one. The glory of the earthly is another.”

In the Aristotelian scheme the universe was divided into the supralunar realm (the celestial) and the sublunar realm (the earthly). All things in the sublunar realm consist of four elements: fire, air, water and earth. The four elements change into one another and constitute the diversity of manifestations in the sublunar realm, especially in the earth’s biosphere. The supralunar or heavenly realm consists exclusively of a wonderful substance Aristotle named Ether: an undifferentiated essence radically different from sublunar essences, and capable only of circular motion at a constant speed around the earth. The circular motion of heavenly bodies was, however, not unconnected with processes in the sublunar region for its produced the succession of night and day, the lunar cycle and the four seasons of the year. Ether is, however, unaffected by transformations in the sublunar earthly zone. Ether is perfect, unchanged by earthly reactions.

Philosophers have observed that the Aristotelian philosophy of a distinction between celestial and earthly bodies was not in agreement with the main trend of Greek thought. Early Greek philosophers preferred to think of the dual realms of nature in unitary terms; a unitary domain in which things interacted in a common matrix of “becoming.”

Aristotelian philosophy appears to have gained popularity because it appealed to common religious sentiments and outlook, for in stressing a distinction between the earthly and the heavenly realms, it reinforced the notion of the earthly realm as being that of mortal beings and the heavenly as being the realm of the immortal gods.

The Aristotelian philosophy of dual essences of the heavens and the earth was acceptable to European Christian theology and was favored by medieval thinkers like Aquinas and Dante. Arising from Aristotelian philosophy was the notion of distinction between “being” as constant realization and “becoming” as an “unfolding of potential.” Underlying the dynamics of “becoming” is the abstract genetic “eidos” of which the given phenomenon is the unfolding realization.

Aristotle conceived of the condition of “becoming” as characteristic of bodies in the earthly sublunar realm. In contrast to the condition of sublunar bodies was a different condition of “being” characteristic of the gods and which was a condition of constantly realized and unchanging state. The gods are constantly and invariably what they are and are incapable of change in the way that a seed transforms in the process of its “becoming” into a tree.

The founding fathers of modern thought, especially in the field of physics, are unanimous in disagreeing with Aristotelianism. Galileo and Descartes, for instance, favored the view of a unitary realm of nature both in the heavenly and earthly domains. Ockham, however, held what appears a self-contradictory position. While he was convinced that heavenly bodies were “incorruptible,” and eternal, he argued that they were of the same kind of essence as earthly bodies, for in his view one must refrain from inferring what was more than necessary.

The final revolution which led to the abandoning of the Aristotelian doctrine of dual heavenly and earthly essences came in the work of Isaac Newton. He was able to show, in his law of Universal Gravitation, that the fundamental laws which operated on earth also guided the motion of bodies in the heavens. With the law of Universal Gravitation, it became obviously unnecessary to postulate different kinds of essences for heavenly bodies and earthly bodies.