For about two thousand years before Galileo, the name which dominated academic circles was Aristotle. Even today Aristotle has high name recognition. During the classical and medieval periods, his popularity resulted in part from the wide variety of topics which he addressed, including: logic, natural philosophy, metaphysics, biology, ethics, psychology, politics, poetics, rhetoric and economics. From Aristotle’s time forward, what he had to say about a subject became the starting point of discussion on that topic. His popularity also was a function of accessibility: many of the writings of classical philosophers had been lost over time and fewer still had been translated into the academic languages of Arabic and Latin. Consequently, the works of Aristotle formed the basis of curriculum throughout the developing university system in medieval Europe.
With such historic esteem, what was it about Aristotle that ultimately caused him to be given him the boot in the realm of science? The strongest criticism against Aristotle involved his ideas about astronomy which came into direct contradiction with Christian theology.
Aristotle conceived of the Prime Mover being at a distance. The Prime Mover resides beyond the celestial sphere and is disinterested in the affairs on earth – the only thing Aristotle’s god thinks about is himself. His influence is limited to maintaining the motion of the heavenly bodies, and is far removed from having any intervening influence on earth. So, while the Prime Mover may be powerful, it is neither imminent nor omnipotent.
Because the heavenly bodies are characterized by regular movements which are unchanging, Aristotle conceived that all things in the heavens are of a different nature, and a different substance (quintessence). To come close to the earth would result in the divine becoming contaminated, and no longer divine. So, the very idea of an incarnation in no way corresponded to Aristotle’s natural philosophy. This also meant it was not possible to truly know or understand the heavenly bodies.
Additionally, from the unchanging nature of the planets, Aristotle deduced they were not created, but were co-eternal with the Prime Mover. This stands in stark contrast to the scriptural stance that the universe was created by God ex nihilo. It also meant that the Prime Mover is not self-existent or independent as one would expect of something truly divine.
While the heavenly bodies are regarded as eternal, the same cannot be said for the things of earth. With earth at the cosmic center, all things made of earth (e.g. humans with their soul included) will move until they find their absolute rest on earth. In other words, humans are not immortal and will not find an eternal place with God after their death – they are subject to decay with no hope of a resurrection.
We say that in his conception of the solar system, Aristotle placed the earth at the center of the universe, but it is more appropriate to say that earth is at the bottom of the universe. Made mostly from the lowest of the five elements, everything falls toward earth. In effect, earth becomes the garbage pile of the universe leaving humans in a lowly estate.
The critiquing of Aristotle, however, had a number of positive influences on the development of science:
As the study of natural philosophy was demonstrated to have a meaningful connection to theology, it made the study of the natural world a reasonable endeavor: a knowable and rational God endowed his creation (i.e., humans) with the ability to reason – the ability to know and understand the universe.
Since many questioned Aristotle’s proposition of the eternal, unchanging existence of the heavenly bodies, it opened the door for questions about how things in the created order came into existence. It was possible to follow a sequence of cause and effect to explain the formation of objects in the world around us – they were not just there from eternity past.
Since the Prime Mover was in question, it opened up the door to consider other possible explanations for planetary movement. This did not remove the necessity for a primary cause for originating and sustaining the universe, but secondary causes could come under consideration along with the natural laws to govern them – laws established by God who brought order out of chaos.
The act of criticism itself with its emphasis on reason and argumentation (utilizing the principles of logic described by Aristotle) helped create a free-thinking environment which allowed the questioning nature of science to develop.
Such criticism demanded evidence to support philosophical propositions, which naturally led into the development and refinement of experimental methods. This was one of Galileo’s important contributions to science as he contested the physics (motion of bodies) described by Aristotle. Rather than simply mounting logical arguments, he devised physical demonstrations to support his premises.
While the casting off of the influence of Aristotle was a slow process, it was the shift to a decidedly Christian worldview that allowed science to become incredibly productive. When the natural philosophers, like Kepler, could view themselves as “thinking their thoughts after God” they were able to open the door to the truth about the universe.