Medieval Cosmology

What one believes about the nature of the universe and one's own place in it is not a trivial matter, and it has profound consequences for how an individual thinks about all aspects of life. Through the teaching that I have done over many years at Knox College (especially in the now defunct First-Year Preceptorial course on "Nature and Culture" and in "History & Systems of Psychology"), I have developed a strong interest in the history of cosmologies, especially the worldview of Medieval Europeans. I am especially interested in how their beliefs about the nature of the physical universe evolved from earlier Greek philosophies and how these beliefs became entangled with Christian Theology through a series of historical accidents.

Plato (428-348 B.C.) believed that there is a realm of abstract forms that is separate from the physical world. Everything in the world is an imperfect copy of one of these "pure" forms. Therefore, when we perceive the world, we are not seeing it as it truly is, but just crude, blurry copies of the forms that represent true reality. To make matters worse, these imperfect copies become distorted by our senses. Consequently, we can never come to know the true nature of the world through observation; the best we can do is form opinions based on faulty information. Plato illustrated his beliefs with many stories. One of the more famous of these is the "Allegory of the Cave."

For Plato, the best path to knowledge was through reflection, introspection, and rational thought. He believed that before the soul was implanted in the body it dwelled among the forms and had full and complete knowledge of them. Thus, we come into the world knowing the truth and through philosophical training we become able to rediscover it.(This view is called his "Reminiscence Theory" of knowledge.) Neoplatonism, primarily through the writings of Plotinus (204-270 A.D.), was a revival of Plato's philosophy during the later stages of the Roman Empire. Plotinus developed the more mystical aspects of Plato's ideas and came very close to turning them into a religion rather than a philosophy. It was St. Augustine (345-430 A.D.) who later adapted Neoplatonism to Christian beliefs, and put together a common core of Christian theology that would dictate the way Western peoples understood the world for almost 1,000 years.

Aristotle (384-322 B.C.) rejected Plato's nativist beliefs and was a hard-nosed empiricist who examined nature directly rather than relying on introspection. He believed that reason was important, but also believed that sensory experience should be the raw material for it. He believed that to truly understand something one must carefully observe it and attempt to determine its four causes. These causes were the material cause(what is it made of?), the formal cause(what form does it take?), the efficient cause(what force shaped it?), and its final cause(why does it exist?).

While early Europeans were aware that Aristotle had existed, access to his work disappeared with the fall of the Roman Empire and it was not rediscovered by Europe until contact with the Arab world increased following the crusades.

From the early through the late Middle Ages, Europeans moved from a disorganized, almost mystical way of thinking about the universe to an acceptance of a well-ordered, geocentric universe based upon the ideas of philosophers such as Ptolemy and Aristotle. In this universe, the Earth was at the center and other heavenly bodies rotated around it in a series of concentric spheres (see the diagram above). The entire system was powered by the primum mobile, or "Prime Mover," which was the outermost sphere set in motion directly by God.

It took some very creative thinking to make this universe work well. For example, the retrograde motion of the planets in which they sometimes seemed to be changing directions and moving backwards was explained by way of "epicycles" (see the diagram below). Specifically, it was proposed that the planets rotated around a center point fixed in place on the sphere of that planet, causing the apparent change in the direction of planetary motion.

Since medieval Europeans had no conception of a vacuum, it was believed that the heavens were filled with a celestial fluid that flowed as the spheres of the universe rotated, thus sustaining the motion of the planets. Furthermore, all of this motion created a beautiful "music of the spheres" which could not be detected by humans (at least not until after they died and went to heaven), but which provided pleasure for angels and other supernatural beings.

The gradual change in European thinking about the nature of the universe was accomplished by way of contact with the Islamic World, where scholars such as Ibn Sina (Avicenna) and Ibn Rushd (Averroes) had preserved much from ancient Greece that had been lost to Western Europe. It was primarily through the work of Christian scholars such as St. Thomas Aquinas that these ancient Greek views about the nature of the universe became welded to Christian Theology in a way that would cause great problems for scientists such as Galileo a few centuries later. Dante, in his "Divine Comedy," put the finishing touches on this Medieval Universe by providing such detailed descriptions of it (including maps of hell, purgatory, and heaven!) that people knew that things just had to be as Dante had described them.