Features of the Aristotelian World View

The universe is finite, spherical, and eternal (has no beginning and no ending).

--Finite because (1) an infinite cosmos would have no center and the universe obviously has a center; and (2) the daily rotation of an infinite cosmos would require that celestial bodies travel an infinite distance in a finite period of time, an absurdity. --Spherical because (1) the perfect shape is the sphere (it contains more volume per surface area than any other shape; also it is perfectly symmetrical—rotate it any way you wish and it looks the same); and (2) nothing exists outside the cosmos; as the cosmos rotates therefore, it cannot move into a place that it does not already occupy. Only a sphere can satisfy this requirement. --Eternal because spheres (and circular orbits) are completed figures; they have no end, beginning, or middle. Eternal means ungenerated and incorruptible; i.e., perfect and immutable.

The universe is divided into two parts, the sublunar (below the moon) and the supralunar (moon and above). Everything in the supralunar region is unchanging (except for stellar and planetary positions) and perfect. Everything in the sublunar region is imperfect, changing, generated, corruptible. The heavens are qualitatively different from the earth. The two regions consist of different substances or elements and are governed by different laws or principles.

Change is explained in terms of potential being (potentiality) and actual being (actuality). The green tomato turns red because the green tomato possesses the potentiality to become a red tomato. As it does so, it actualizes as a red tomato—it becomes what it truly is. (Actual things are more real than potential things.)

Causality consists of four aspects: (1) material cause (what an object is made of); (2) formal cause (its form or shape); (3) efficient or motive cause (what brought the object into existence, its maker); (4) final cause (its purpose or end). The concept of final cause makes Aristotle’s worldview teleological or goal-oriented. Not everything happens because of prior causes (as modern science purports); much, perhaps the most important things, happens because reality is responsive to final causes existing in the future.

There are five kinds of elements in the universe. In the sublunar region we find earth, air, fire, and water. Earth and water have gravitas and naturally move downwards in a rectilinear fashion (toward the center of the earth which is the center of the cosmos). Air and fire have levitas and naturally move upwards in a rectilinear fashion (away from the center of the earth). In the supralunar region we find the fifth element that is variously called ether, quintessence, and ethereal fire. Ether is neither heavy nor light (has neither gravitas nor levitas) and so moves in such a fashion as to neither approach the center of the universe nor recede from it. This can only be in a circular fashion.

Motion in the sublunar region is of two types: natural and unnatural (forced or violent). Natural sublunar motion is either upwards or downwards from the earth’s center in a rectilinear fashion. Unnatural motion involves forcing an object to deviate from its natural motion. For example, when I throw a ball, I force it to travel horizontally, at least for a brief time. When that force is exhausted, the ball’s natural motion takes over and it falls vertically to the earth.

Natural motion can be understood in terms of natural place. Everything in the universe has its natural place and natural motion is movement toward that place. A rock falls downward toward the earth because that is where it came from and it “wants” to return home. (Think of things having sympathies and antipathies; the rock “inclines” toward earth and “disinclines” to be removed from it.) Any attempt to remove or keep an object from its natural place involves unnatural motion. Note that for Aristotle rest is an object’s natural state, for when an object is at “home,” it is at rest. A moving object is one not fully arrived, as it were, and therefore suffers a want or lack.

All this implies a teleological universe, one governed more by final causes than by antecedent or prior causes. Even rocks are sentient and therefore suffer when they are moved from their natural place. On a grander scale, everything is lifted upward by some glorious future prospect—some final cause that informs the universe with purpose. Ultimately this is Aristotle’s Prime Mover or Unmoved Mover. The sublime perfection of the Unmoved Mover inspires motion in the cosmos but does not move itself. (If it did move, that would imply imperfection.) Think of the Unmoved Mover as something like a static light or candle flame whose beauty or luminous “perfection” causes moths to circle around it. What are the characteristics of the Unmoved Mover? You can infer them from Aristotelian principles. First, the Unmoved Mover is pure actuality: he has no potentiality because such would imply change and the present lack of perfection. Second, since Aristotle believes that the transformation of potentiality into actuality entails movement away from physicality, the Unmoved Mover is immaterial or non-physical. (Note that Aristotle, like Plato, believes that perfection cannot be realized in the physical realm.) Third, since thinking or intellectual reflection is the highest of all activities, according to Aristotle, the Unmoved Mover is something like pure thought or intellect. And, fourth, since the Unmoved Mover thinks only about that which is absolutely perfect, he thinks only about himself. He is oblivious to you and me and to the entire cosmos.

The earth, because of its gravitas, is at the center of the universe and is immobile. Its natural position in the cosmos is one that is equidistant from all parts of the spherical surface of the cosmos. Thus, the center of the earth is the center of the universe. The starry heavens rotate daily around the earth. (This violates our sense of economy since it seems much easier to have the small earth rotate rather than the entire universe, but for Aristotle the earth is heavy and the heavens are not heavy at all. Therefore it is easier and more economical for the heavens to rotate. Besides, circular motion is their natural motion. One might say the heavens rotate effortlessly.)

The heavens are made up of concentric spheres nested inside one another. Embedded within these spheres are stars and planets. These bodies are composed of ether and do not (as we imagine) hang in midair. It is not clear why, in view of the fact that the stars and spheres are composed of the same element, the stars are visible and the spheres are not. Perhaps the stars are points of friction between neighboring spheres. Or, they might be extremely dense concentrations of ether.