The Late Medieval Paradigm Shift

Most people think of late medieval times as a dark time of superstition and intellectual stagnation. It is commonly believed that the Church enforced a vicious anti-rational mentality, stamping out independent thought. 

Nothing could be further from the truth. It is certainly true that times were tough in the early Middle Ages — say, from 400 CE to 1000 CE — but that had more to do with political instability than religious fanaticism. But I’m talking about the period from about 1200 CE to 1600 CE, comprising the late Middle Ages and the Rennaissance. During this period, the Church was in fact the patron and organizing force behind what I believe to be the greatest intellectual leap in human experience. What these people did during that period is simply astounding. But to understand the magnitude of their achievement, you need to know how they got they started.

The discovery of Aristotle
The works of Aristotle became widely available in Christendom around 1200 CE. At that time, there simply wasn’t any place to get a good education in Western Europe, so the Church sent the brightest scholars to Spain and Sicily to study in the cosmopolitan atmospheres of these enlightened societies. There they learned from Islamic and Jewish scholars who were, quite frankly, way ahead of the Christians. They had glommed onto Greek literature centuries earlier and had extended and improved upon it. The excited Christian scholars brought home word of this ‘new learning’, especially the works of Aristotle. 

It took decades for the great works of Aristotle to be translated into Latin and spread all over the continent; when it can take months to copy a single book, the process was slow. But by the standards of those times, Aristotelian thought spread like wildfire through Christendom. The newly established universities were chary of all this at first, but it didn’t take the works of Aristotle to pass from banned pagan heresy to required reading. 

Do not forget that all of this was done by the Church. In those days, the Church was the only institution promoting learning. All education took place in Church facilities, with Church personnel doing the teaching. They would accept laity for low-level education, but anything beyond basic literacy was available only to the ordained. Education in those days was inordinately expensive and the Church wasn’t about to spend its money educating people who weren’t part of the organization. 

Within that stricture, however, the Church was extremely liberal in its intellectual tolerance. The best and the brightest were encouraged to explore the world of ideas. As Thomas Aquinas put it, the more we understand the universe, the better we appreciate God’s glory. I’m not sure if most Christian thinkers really felt this way, but was a great sales line and it worked fabulously: the Church lavished funds upon its expanding network of universities. The top school was the University of Paris, but Oxford was not that far behind, and there was a galaxy of great universities in Italy. 

It’s difficult for modern people to realize just how lavish this program was. In those days, there just wasn’t much wealth to spread around. The aristocracy hogged most of it, but as the Church’s wealth and power grew, it devoted an ever-growing portion of its income on education. Thus, there arose an entire community of researchers. This was unprecedented. Other societies had maintained tiny cliques of scholars — mostly ‘astronomers’ whose most important job was really astrology. Greek and Islamic society had their own intellectuals, but these were rarely state-supported; for the most part they were people wealthy enough to be able to pursue research on their own dime. 

Moreover, the Church’s effort was sustained over centuries, while the research efforts in other civilizations were driven by the varying tastes of a succession of grand poobahs. One big shot might fund a lavish research effort, but then it would all fall apart when his successor decided that war was more fun. The Church, by contrast, funded a major effort for centuries. 

This huge outlay drove an energetic program of intellectual inquiry. But their starting point was Aristotelianism, which was way wrong. This essay is the story of how Church scholars transformed Aristotelianism into modern science.

Aristotelian Physics
I’ll focus on a single aspect of Aristotelian thought: the explanation of motion. Aristotle held that motion was controlled by two factors: a driving force and a natural resistance; objects moved only when the driving force exceeded the natural resistance. 

None of this was expressed in the mathematical terms we now use; instead, they used clumsy verbal constructions to communicate ideas that we can express in a short equation. For example, they often talked in terms of the effects of doubling or halving some factor; this was the best way they could think of to express their thoughts. Aristotle held that, if you double the force on something, then its speed doubles. Alternatively, if you double its resistance, then its speed halves. That idea is easily expressed in modern mathematical terminology:

v = aF/R

or fleshed out:

velocity = proportionality constant * force / resistance

There was a nasty little gotcha in all this: what happens if an object exists in a vacuum? In a vacuum, there should be zero resistance to motion, in which case everything would move at infinite velocity. This was so absurd that Aristotle, instead of abandoning his initial idea, concluded that a vacuum was a physical impossibility. This little bit of illogic caused centuries of hand-wringing among Christian scholars. Other arguments suggested that a vacuum should be theoretically possible, but Aristotle denied that. Much ink was sprayed over many pages trying to resolve the dilemma. 

Why do things fall?
Aristotle’s next booboo was his explanation of why things fall without any apparent force working on them. His version had it that there were four basic elements of which everything of was made: earth, water, air, and fire. There is a cute but misleading interpretation of this; his four elements correspond neatly to the four states of matter: solid, liquid, gas, and plasma. Don’t get too excited about it: it was just coincidence and Aristotle managed to contaminate the idea. He argued that every one of the elements had a natural proclivity to move either towards or away from the center of the universe (which just happened to be the center of the earth). Earth had a strong ‘natural drive’ to go to the center of the universe; water’s drive was lesser. Air preferred to move away from the center of the universe, and fire was highly motivated to get away from the center of the universe. 

Since everything in the universe was composed of these four elements, every object's behavior was determined by the predominant element in each object. A chunk of lead was completely earthen, and so it had a strong drive to move downward. Wood was mostly air mixed with some earth, so it floated on top of water. And so on.

Thus, downward motion was easily explained by the ‘natural drives’ of the elements. The resistance of the medium through which the object moved determined the speed of its fall. A stone falling through the air would fall rapidly, but it would slow down on entering water. 

Bigger rocks had a stronger downward drive than small rocks; therefore they fell at greater velocity. Until Galileo came along, nobody bothered to actually check this out, largely because things fall so quickly that experiments on falling objects never yielded decisive results. What if there had been no Leaning Tower of Pisa?

Why do things move upwards or sideways?
But this didn’t explain how objects came to move when thrown. The problem lay in the motion of the object once it leaves the hand that throws it. It’s easy to see that the hand provides the impelling force before the object leaves the hand, but what happens when the object leaves the hand and is no longer subject to that force? Aristotle pulled a rabbit out of his hat: the air rushes behind the object and continues pushing it for a while, but the air loses its strength, and the object falls. 

We moderns can easily laugh at this nonsense; after all, any nincompoop can see the problem:


Aristotle’s version has the thing falling steeply at the end of its flight, but we all know that in fact the flight is more symmetrical than that. The problem here is it takes a sharp eye to observe this in practice, or highly contrived circumstances. Most people never noticed because they just didn’t watch that closely. 

Escaping from Aristotle’s web
Part of the problem the medieval scholars faced was that Aristotle had assembled a huge body of thought, all closely tied together. In effect, Aristotle had carefully constructed a “Theory of Everything” that worked pretty well in so many cases that it seemed idiotic to chip away at minor bits here and there. The fact that he seemed to be wrong in one detail didn’t necessarily mean that his basic theory was wrong; perhaps it was just a matter of fleshing out the details more precisely.

That’s what most scholars thought they were doing. Nobody set out to shoot down Aristotelian thought. Instead, they figured that their task was to fill in the little details that The Great Man had never bothered with. Aristotle had figured out the Big Idea; we little men of the Middle Ages should merely polish and refine his work. 

But they kept running into problems like the one above, and, bit by bit, the scholarly community began to feel a certain discomfort with Aristotelian physics. It just didn’t quite make sense. So in the next phase, they began developing patches, “minor adjustments” to Aristotelian physics that “restored it to perfection”. Wink, wink, nod, nod.

Internal Resistance
The first patch came by thinking in quantitative terms about the composition of an object. Aristotle had declared that an object’s force downward was determined by which element predominated in its composition. Medieval scholars refined this by introducing the relative abundances of the different elements. This differentiated between an object that was 100% earth and another object that was 60% earth and 40% air, such as a piece of pumice. This refinement better explained the behavior of falling objects. 

The next step was to separate the forces inside the object into two counteracting forces: a downward force derived from the earth and water components, and an internal resistance derived from the air and fire components. For upward motion, the roles were reversed but the concept was the same.

Once the medievals had separated the two factors, they were able to rephrase the problem in a crucially different manner: the two competing factors were the force driving the downward motion, and the internal resistance opposing it. Next, this internal resistance evolved into something like what we call inertia, which had the crucial capability of resisting CHANGE in motion rather than force itself. If you threw a rock into the air, you conferred positive inertia that continued to drive it upward even after it left your hand. 

Eventually this morphed into a three-factor approach: the gravitational force (or impulse delivered by a thrower), the inertia of the object, and the external frictional force acting on the object. When you analyzed motion with these three ideas, it made a lot more sense. It wasn’t until Galileo came along that the ideas were clearly and precisely enunciated, and we had to wait for Newton to put them into mathematical form, but remember: they were building on the ideas developed by their forebears of the late Middle Ages.

The other big step forward, quantitative thinking, also took centuries, creeping in on little cat feet rather than exploding forward in one spectacular discovery. Bit by bit, the Christian scholars of the late Middle Ages brought quantitative approaches into their analyses. This set the stage for the first analysis to rely entirely on quantitative figuring: Copernicus’ heliocentric system, published in 1543 but developed decades earlier. 

In 1200 CE, the Christian scholars inherited Aristotle’s deeply flawed system of physics. Bit by bit, they transformed it, using careful reasoning. None of this was explicitly based on empirical evidence. They “out-Aristotled” Aristotle in that they used logic more precisely and more rigorously to detect and correct the fundamental errors in his thinking. It was a slow process involving many steps; the version I have presented here is much cleaner and clearer than the many halting steps, blind alleys, and furious debates that attended this process. But they laid the foundations for true science. Copernicus, Galileo, and Newton did not materialize out of thin air; instead, they walked further down the path that the medieval scholars had prepared. By the year 1500 CE, the rise of modern science in Europe was inevitable in the same way that the steam engine made the Industrial Revolution inevitable, or the transistor made the Information Revolution inevitable. And we owe it all to a bunch of mousy medieval scholars, few of whose names are recognizable: Thomas Aquinas, Roger Bacon, John Buridan, Franciscus de Marchia, William Heytesbury, John Dumbleton,  Robert Grosseteste, and Richard Swineshead. These giants forged a paradigm shift whose magnitude has never been equalled.