The Rules of Nature. One area of science in which the medieval philosophers excelled, discussing important and fundamental concepts of the way nature works, was physics. Because medieval philosophers believed that knowledge of the material world would bring them closer to an understanding of the divine nature of that world, the study of "physiea"—the orderly part of nature subject to rules and to cause and effect—was easily accepted in church schools across Europe. The areas most frequently investigated were motion and optics. Studies of both benefited immensely from twelfth-century translations of ancient Greek sources and medieval Arabic commentaries.

Motion. Aristotle taught that all motions are made up of natural motion and violent motion. This theory explains how things move, but it did little to explain why they moved. (In fact, it was even somewhat unsatisfactory in...