Abstract

In Book Eight of the Physics Aristotle states that explaining the natural motion of heavy and light bodies presents "the greatest difficulty." It should not surprise us then, that his account was read in various ways by medieval commentators and that difficulties remain in understanding the peripatetic explanation. ;My dissertation addresses the issue of gravitational motion in the thought of Thomas Aquinas. First, I consider his account of heavy and light motion in a textual way, looking to key discussions in his Aristotelian commentaries. Here I also consider the historical context of these discussions by examining the writings of Averroes and Albert the Great. Second, I take up a modern interpretive dispute. ;The modern dispute hinges on the teaching that omne quod movetur ab alio movetur. This peripatetic principle has traditionally been interpreted to mean that everything in motion is moved by another. But if this is the case what moves a heavy or light body as it hurtles toward its proper place? One answer often offered is the substantial form of the body. ;Fr. James Weisheipl rejects this understanding. He claims that the principle only requires that everything which is moved is moved by another. On this view there is no need to assign a mover to the heavy or light body already in motion. ;Weisheipl correctly rejects the view that the substantial form moves the gravitating body. On this point Aquinas is quite clear. But Weisheipl is wrong to reject the traditional interpretation of omne quod movetur ab alio movetur. What then moves heavy and light bodies? ;For Aquinas the generator moves such bodies throughout their natural motions. This efficiency is best understood when approached through his foundational discussions of causality in his comments on Physics 2. Here it becomes clear that the generator causes gravitational motion in the same way that a counselor causes action. ;In sum, Aquinas maintains the traditional understanding that bodies in motion are moved ab alio, and that the requirements of this principle are adequately met by the generator and the removens impedimentum