In the first part of this essay, I argued that modern science stands as one of the great achievements of Western civilization. Moreover—and despite what we have often heard—it is certainly an achievement of the West, not of Islam, China or even ancient Greece. So what was it about the West in the medieval period that set the stage for the spectacular advance of science in the centuries to follow? To begin with, I’d like to describe the way the Church reframed the insights of Classical and Islamic culture as they recovered them, freeing European thinkers to explore the world God made in new ways, via both intellectual and experimental practice. Then we’ll turn to the way Christian theology presumed that the free, reliable and good God could be known and honored by looking at His works in creation.
Breaking with Aristotle
In 1085, the great Islamic city of Toledo in Spain fell to Alfonso VI, King of Castile (left). Christian forces captured its magnificent libraries intact and word soon spread about the fabulous riches contained therein. Europeans were well aware that they had lost much of the learning of the ancient world after the fall of Rome and they were keen to reacquire it. The resulting movement to translate Arabic and Greek scholarship into Latin meant that by 1200, Christians were back up to speed in science and math.
Initially, some churchmen were suspicious about all this new knowledge and feared that it would be misused to challenge the faith. When a nest of heretics was found in Paris and its environs, the resulting panic led to a temporary ban on Aristotle’s natural philosophy at the university there. Scholars were furious and demanded that the forbidden books were reinstated. So, after a decent interval, the Pope rescinded the ban and Aristotle took his place at the heart of Christian education.
As we saw before, the danger of Aristotle was in his method. It was bad enough that several of his conclusions contradicted revealed theology. But the problem went deeper than that. Because he had tried to arrive at results deductively, Aristotle made his conclusions seem logically necessary. His admirers did not just claim that he was right, they said he had to be right. In effect, Aristotle’s most dedicated followers were agreed that God Himself was bound by what Aristotle thought because, despite His omnipotence, even the Deity could not defy logic. But, in reality, most of Aristotle's natural philosophy was wrong. Science could go nowhere until the dead hand of the Greek sage was lifted from it.
The Church had to deal with this, even though it was primarily interested in theology and not science. In 1277, the bishop of Paris, with papal approval, issued a list of opinions, drawn from the work of Aristotle and his medieval followers, which he declared heretical. The effect was paradoxically liberating. All of a sudden, European philosophers were freed to think outside the Aristotelian box. No longer could they assume that the Greeks were always right. Thus, if God willed it, vacuums were no longer deemed impossible. There could even be more than one universe. Now natural philosophers could speculate on all sorts of things previously ruled out of court. The result was that the fourteenth century became a scientific golden age when much of the groundwork was laid for ideas that later ended up in the books of Copernicus and Galileo. Let me give a couple of examples.
Medieval sources of Renaissance discoveries
Copernicus, of course, is famous for proposing that the earth rotates and orbits the sun, rather than being stationary in the center of the universe, as Aristotle had taught. It is perfectly sensible to believe that the Earth is at rest, especially given that we cannot feel it moving. However, in fourteenth-century Paris, the philosopher John Buridan and his student Nicole Oresme developed the arguments (pictured right), later used by Copernicus, to explain why we cannot tell if the Earth is in motion. Aristotle proposed that the universe turns around the Earth each day. Buridan asked why it cannot be the other way around, realizing that what we observe would be exactly the same. He used the analogy of someone one a boat:
If anyone is in a moving ship and imagines that he is at rest, then should he see another ship, which is truly at rest, it will appear to him that the other ship is moved ... And so, we also posit that the sphere of the sun is everywhere at rest and the earth in carrying us would be rotated.
Compare that to the argument used by Copernicus in his book, On the Revolutions of the Heavenly Spheres:
When a ship sails on a tranquil sea, all the things outside seem to the voyagers to be moving in a pattern that is an image of their own. They think, on the contrary, that they are themselves and all the things with them are at rest. So, it can easily happen in the case of the earth that the whole universe should be believed to be moving in a circle [while the earth is at rest].
Of course, like other Renaissance writers, Copernicus never acknowledges his debt to his medieval predecessors. Rather, he quotes a line from Virgil’s Aeneid, giving his argument a wholly bogus classical gloss. For what it’s worth, Copernicus also used the fruits of Islamic mathematical astronomy without attribution. As the fashion of his time demanded, he would only admit to using Greek and Roman sources.
Despite his correct argument about relative motion, John Buridan eventually decided that the Earth was not moving. He imagined that if it was rotating, an arrow fired straight into the air would land some distance away because the Earth would have moved before it reached the ground. His pupil, Nicole Oresme, realized this argument was false because the arrow inherits the motion of the Earth when it is fired. So, the Earth, bowman and arrow are all rotating together. Galileo covers these thought experiments in great deal in his Dialogue Concerning the Two Chief World Systems (for which he was put on trial by Pope Urban VIII). But you would never guess from Galileo’s text that his arguments are actually rather old hat.
Even Galileo’s most important work, Dialogues on Two New Sciences, contains strong echoes of ideas developed in the fourteenth century. The formula he derives for the motion of a uniformly accelerating body was really discovered in fourteenth-century Oxford at Merton College. And the diagrammatic proof that Galileo provides for this theorem was first illustrated by Nicole Oresme himself.
There can no longer be any doubt that the pioneers of early modern science were far more indebted to their medieval predecessors than they were inclined to admit. But by the sixteenth century, humanism, the political correctness of its day, meant that it was respectable to acknowledge the influence of the classical world while denigrating the Middle Ages. To a great extent, this is still true today.
Science as practical theology
The importance of medieval science extends beyond simply providing the theories that early modern scientists exploited. Medieval Christian theologians also developed the metaphysical framework within which it made sense to practice science at all.
Given today’s perceptions of a conflict between science and religion, it is surprising to find that Christianity has proved to be uniquely accommodating to the study of nature. While there is little in the Bible that could be called science, the book of Genesis is very clear about where the universe came from. Contrary to Aristotle’s view that it is eternal, the Bible says that God made the world at the beginning of time. Christians believe that the world was created ex nihilo, out of nothing. God did not have to work from pre-existing material that resisted His purposes. This meant, as Genesis affirms, that the creation turned out ‘good’ and as God wished it to be. Christian theologians held that He had also allowed the world to develop freely through natural laws which He had ordained. The order of nature followed these laws rather than God personally having to manipulate each atom.
The twelfth-century, William of Conches had already realized this when he wrote:
I take nothing away from God. All things that are in the world were made by God, except evil. But He made other things through the operation of nature which is the instrument of divine operation.
Another feature of the Christian God was is reliability. He is not capricious like the Olympians of ancient Greece or entirely beyond human comprehension, like Allah. This meant that natural philosophers knew that they could depend on the laws that He had laid down. Nature itself should reflect her creator by obeying His commandments. This gave Christians good reason to believe that science was a practical venture; that nature did follow fixed laws that could be discovered. This view was expressed by Thierry of Chartres, another theologian of the twelfth century:
Because the things in the world are mutable and corruptible, it is necessary that they should have an author. Because they are arranged in a rational way and in a very beautiful order, it is necessary that they should have been created in accordance with wisdom. But, because the Creator, rationally speaking, is in need of nothing, having perfection and sufficiency in himself, it is necessary that he should create what he does create only through benevolence and love.
Science was also a theologically righteous path to pursue. Since the world was created by God, exploring how it works does honor to its Creator. And because science studies the ordinary course of nature, it was not necessary to worry about the rare occasions that God does intervene directly through miracles. John Buridan explained in the fourteenth century, “it is evident to us that every fire is hot, even though the contrary is possible by God’s power. And it is evidence of this sort that suffices for the principles and conclusions of science.”
Nonetheless, because God was free to do as He pleased, Christians realized it was impossible to work out the laws of nature from rational analysis alone. The only way to discover His plan was to go out and look. This principle of God’s freedom and absolute power was asserted by the bishop of Paris in 1277. It meant that science could not rely on pure reason to generate theories, still less Aristotle’s “logically necessary” conclusions. God created the world in the way He wished to, not the way Aristotle said He had to.
Of course, medieval natural philosophers no more had in mind the development of modern science than the ancient Greeks had. Christians practiced science to serve theology, just like pagan natural philosophy had served ethics. Specifically, scholars of the Middle Ages wanted to understand the universe in a way that made sense of their religious beliefs. They saw the world as a place that was God’s creation but one which also had its own freedom and integrity. It was a place where human beings could make real moral decisions that had real consequences. It just so happens that their metaphysical were especially conducive to science.
Given the advantages that the religion provided, it is hardly surprising that modern science has only developed within a Christian milieu. Although it is possible that other religious traditions could have provided a similarly fertile metaphysical ground for the study of nature, none that we know of have actually done so. Nor is it startling to find that Copernicus, Kepler and Galileo worked within the framework of medieval natural philosophy, rather than in a transplanted ancient Greek tradition. It seems fair to conclude that Christianity was an important cause of the unique development of western science, the only science which has consistently produced true theories of nature.