Aristotle vs Galileo: Review of Galileo's Dialogue by Maurice Finocchiaro

For two thousand years, Aristotle's worldview held sway for Western civilization. Aristotle believed that the Earth was geostatic (unmoving) and geocentric (the focal and central point of the universe). As to whether the earth was flat or round, this was something that was actually beyond debate in those times.

In fact, only the uneducated and primitive people believed the earth to be flat. This issue about the shape of the earth had already been settled by philosophers and scientists, and they did not think the earth to be flat. It may come as a surprise that certain people would insist otherwise despite evidence to the contrary, but we do not need to look too far today, i.e. intelligent design to find similar strains of foolishness floating around.

The whole Copernican controversy was more about the earth's location, whether it had a geocentric or heliocentric position, and its behavior, whether it was static or moving. As mentioned, the Aristotelian worldview of the earth as motionless and geocentric stood firm for two thousand years until the heliocentric Copernican revolution toppled it over.

According to the Aristotelian worldview and philosophy, there are fundamental pairs of physical opposites of hot and cold, humid and dry in the universe. These pairs are then combined to create the four elements, where earth consists of cold and dry; water is a mixture of cold and humid; air a combination of hot and humid, while fire was thought to be made of hot and dry.

Depending on its materials, each element would have a specific given and natural direction. For example, earth and water would generally move straight downwards, while air and fire would move straight upwards. This underscores the reasoning behind and concept of natural motion. Bodies tend to move toward their natural and proper resting place. And, in fact, motion is the opposite of rest since once bodies have found their place, they will not budge unless moved by others, that is an external agent.

So we can see Aristotle believed that earth and water have weight (gravity) and are hence “heavy bodies.” The natural state of bodies is that they remain at rest. Hence in such a worldview a rotating earth did not make much sense.

Moreover, it is important to note that bodies on earth do no emit light much unlike the stars that are in the heavenly spheres. Even fire does not emit its own light but only does so when it is escaping from the lower regions to find its own proper place upwards, that is in the heavenly spheres.

While the heavy bodies tend to be at rest on our planet, air and water have levity and are light bodies; these light bodies are helped to travel via the fifth (and most mysterious) element called aether, which was supposed to be luminous, this being one of its most significant properties or characteristics.

Now nothing moves on its own as all bodies prefer to reach the natural end state of motion, which is its opposite, namely rest. They would remain so because that is their internal state. Once they have found this state, they can be moved only externally, that is by an external agent, which can be a person, for example, picking up a pebble from the beach and throwing it, or the wind that is blowing the leaves about.

So if the heavenly spheres are rotating around the center of universe, they must be started by some mover, in fact, the sublimely mysterious unmoved mover. This motion is referred to as primum mobile, meaning simply the first body in motion. It is these constantly moving spheres that carry planets and stars with them in continuous circular motion.

Where the earth's natural state is bodies at rest, the important characteristic of the heavens is motion. (In fact, in the heavenly sphere, there are both fixed and wandering stars. Only seven of these stars were considered to be wandering and hence they were called planets, which means, yes, wandering star.)

Not bad, Aristotle, but in comes Copernicus to shake things up a little and to put things upside down. Copernicus proposed a heliocentric model and that the earth was not static but moving. In fact, the ideas of Copernicus were not new but had already been proposed by ancient Greek philosopher Pythagoras and others; what Copernicus did was merely reinterpret the available information.

One of the strong points of Copernican theory was that his explanation was simpler, more elegant and more systematic because instead of having the heavenly spheres with thousands of stars moving about, there is only one body moving, namely the earth.

This heliocentric theory was approached like any body in motion, that is, with resistance and opposition. This resistance occurred due to biblical objections. The Protestants who had a more literal approach and interpretation of the Scripture tended to object the most and strongest.

When it came to the Catholics, they referred, when in doubt, to the Church Fathers for guidance and illumination. And it turned out that pretty much all of these noteworthy fathers put Aristotle on a pedestal and believed that the geostatic system was the correct one to be espoused, while anything that was otherwise ought to be officially declared as heretical. That also became the Church's official position until rather recently when the Church in 1992 accepted that Galileo was right after all, more than 350 years later!

So after Copernicus the grounds were set for Galileo to enter the scene. Galileo following his father's footsteps used the experimental approach for his findings and discoveries. In fact, one of his greatest and most revolutionary deeds of the times was to point the telescope upwards to watch the skies. His new and improved lenses made leaps and bounds in astronomy and added precision since his observations ended up being much more reliable than naked-eye observations.

But alas, Galileo was not given free reign in his discoveries. He was considered a heretic by the Inquisition who deemed his proposed theories on the earth's motion as false and as a dangerous threat to Catholicism as a whole. Galileo had lost his general support in the Vatican and was threatened with torture on the basis of “vehement suspicion of heresy.” However, he managed to escape a lengthy prison sentence and it all lead to house arrest instead.

Why was the Church so obsessed with the earth's position and motion and so opposed to the new science? One of the reasons apart from scriptural authority was that the world was seen as a perfect embodiment created by God, or rather His unique masterpiece. This led to a view of teleological anthropocentrism, which means that the whole universe exists merely for the sake and benefit of humankind.

This is also related to Aristotle's view regarding heavenly bodies, which are closer to God and are perfect in themselves because they do not change and hence are eternal like its Creator. On the other hand, the earth is far from perfect. We find that the earth changes and that life and things down here are corrupt and dirty; they die and decompose and thus have transitory existence.

It is through pure mathematics that we can reveal God's works since mathematics as opposed to the sciences gives us the same objective certainty that God has. There is no - or much less resistance to - doubt, whereas in other fields we must be aware of our senses, which can, according to Plato, deceive us in various ways.

Yet it is important to note that Galileo is not using one method but rather relies on logic (apart from physics naturally) in his arguments, logic not in the sense of a theory of reasoning but which also includes theories of knowledge, as method as well as science. He combines his observations of moving ships and gunshots (all of which went beyond my own head and my limited reasoning capacities) with detailed logical analysis.

As a result, his Dialogue becomes a synthesis of astronomy, physics, and epistemology. It is, in fact, a fascinating work and it is presented in detail and with clearly presented arguments and reasons in The Routledge Guidebook to Galileo's Dialogue written and expounded expertly by Maurice A. Finocchiaro, albeit the book is at times too complicated and complex for this scientifically and logically untrained mind of mine. 

My only caveat is that those who would like to read this guidebook to better understand Galileo's work and theory be better equipped with some physics and mounds of logic, and thus they will reap even more benefits than I was able to unearth for myself.