The Discarded Image

Plenitude is one of the central tenets of the Medieval Model. It originates from Apuleius, though he took inspiration from Plato. The idea of Plenitude is that each realm of the universe must be occupied with its own lifeforms. The realm above the orbit of the moon, which most people would now understand to be the void of outer space, was thought to be the realm of the spheres, as described below. The surface of the Earth was the realm of humans, animals, and plants. In between these two realms was the aether, a vast airy space. In accordance with the principle of Plenitude, medieval people believed that the aether was home to “daemons,” or spirits that could be variously understood as lower-ranking angels, malevolent demons, or other spirit-like creatures.

The Medieval Model was primarily predicated on a Ptolemaic model of the universe. This was a geocentric model that placed Earth at the center of the universe, with a few planets, the sun, and the moon all orbiting it. The other stars were thought to be fixed in an outer, solid vault of the sky. According to this model, the universe was not a dark and infinite void. Instead, it was a finite space that was predominantly light and warm. The darkness of night was merely the moving shadow of the Earth. This view of the universe was carefully ordered. Because it assumed that Earth was at the center of the universe, the Ptolemaic model had to include epicycles, or little loops, in the orbits of each planet. These epicycles were among the few imperfect or rather clumsy elements of an otherwise highly regular conception of planetary movement in the universe.

Many things in the Medieval Model fit into tidy sets of three. This is of course true of the Christian trinity—the Father, the Son, and the Holy Spirit—but it is also true of many other subjects contemplated by medieval thinkers. Lewis notes that people in the Medieval Era divided the universe into three zones: Earth, the aether, and the translunary region. They also understood humans to have a threefold soul that consisted of Rational, Sensitive, and Vegetable elements. The medieval love of the Triad speaks to the theme of The Prevalence of Hierarchy and Order, which is prevalent throughout medieval literature. Although many people now associate the idea of a triad or trinity with Christianity, it is actually one of many medieval concepts that developed at least in part because of the influence of pre-Christian, classical civilizations.