Back in 1978, Carl Sagan included a time line of scientific progress in his book Cosmos , showing that nothing at all happened between a.d. 415 and a.d. 1543. This barren period, he implied, was caused by the thousand-year dominance of Christianity. The “conflict thesis” of science and religion was born in the salons of ancien régime France, where philosophes like Voltaire and d’Alembert used it as a weapon against the Catholic Church. It was further developed in Victorian England by T. H. Huxley in his battle to diminish the influence of the clergy in London’s Royal Society. And it was perfected in American universities by the likes of Andrew Dickson White, the first president of Cornell University, who provided the theory with intellectual ballast in his heavily annotated A History of the Warfare of Science with Theology at the end of the nineteenth century. It has been promoted in countless articles in popular magazines and elementary-school textbooks.

The history of science is the story of how we went from being fundamentally wrong about the natural world to being, in large part, right. Science as we imagine it today”with laboratories, experiments, and a professional culture”did not appear until the nineteenth century, but its origins can be found much earlier, in the period commonly known as the “scientific revolution.” And the “scientific revolution” was a continuation of developments that started deep in the Middle Ages among people whose scientific work expressed their religious belief. The conflict thesis, in other words, is a myth.

The thesis rests on two further myths about scientific progress. First, many people still believe that science has advanced by fighting religious superstition and making the world safe for rational inquiry. It is true that certain religious doctrines contradict some scientific discoveries. The creation/evolution controversy is a case in point, but such quarrels have been surprisingly rare. Even the infamous trial of Galileo, the other example of conflict most often cited, was an aberration in the Catholic Church’s usual supportive attitude toward science.

The “scientific revolution” in the seventeenth century coincided with the period when Christian belief in Europe was at its strongest. Only after science had triumphed did religion start to suffer any sort of decline. And, if Christianity had tried to hold back scientific progress, the chances are that it would have succeeded. Modern science would not have arisen in Christian Europe at all.

As it happens, much of the evidence marshaled in favor of the conflict thesis turns out to be bogus. The Church never tried to outlaw the number zero or human dissection; no one was burnt at the stake for scientific ideas; and no educated person in the Middle Ages thought that the world was flat, whatever interpretations of the Bible might imply. Popes have had better things to do than ban vaccination or lightning conductors on churches. The thought of a pope excommunicating Halley’s Comet is absurd, but this has not prevented the tale of Calixtus III doing just that from entering scientific folklore.

It is remarkable that authors who consider themselves skeptics can swallow some of these stories whole. For instance, Sagan introduced his readers to a “baloney detector” in his later book, The Demon-Haunted World . It is a great shame he never used it on his own writings. In Cosmos he presented a completely fictitious account of the murder of the pagan philosopher Hypatia and falsely blamed Christians for the destruction of the Alexandrian library.

Zealous Victorian historians did find occasional examples of ecclesiastical stupidity, such as the Boston pastor who warned that lightning caused earthquakes. They rewrote history to make these marginal figures into leaders of opinion. Religious dissidents who paid the ultimate price for their faith were recast as champions of reason. Pope Boniface VIII issued a bull intended to stop crusaders from sending their bones home for burial. He would have been most surprised to hear that, according to Andrew Dickson White, he had in fact legislated against human dissection. When priests questioned a scientific theory, which they often did in their capacity as amateur scientists, their scientific skepticism was held up as an example of religious obstruction. Historians have been debunking these legends for over a century now, but each new generation of popular writers continues to recycle them.

But the legends are false, and their falsity suggests the problem. Modern science stands as one of the great achievements of Western civilization”not of Islam, China, or even ancient Greece. Many historians of science are still reluctant to admit this. They praise ancient Greek and Arabic sciences as successful on their own terms but have lost sight of the fact that the theories advanced by early science were largely false.

The second myth about the rise of science is that Westerners only picked up the baton from the ancient Greeks, or, as has been more recently alleged, the Islamic caliphate. The undefended corollary of the idea that the Church has held back scientific progress is that we must look outside Christendom to discover the origin of modern science. In reality, modern science is qualitatively different from the natural philosophy practiced by the likes of Aristotle or Avicenna. Aristotle started from the passive observation of nature and then built up a system based on rational argument. This had two enormous disadvantages: Compared to controlled experiments, passive observation is usually misleading, and not even Aristotle’s powers of reason could prevent blunders in his arguments.

His discussion of motion is a case in point. He observed that everyday objects tend to stop when nothing is pushing them and deduced the principle that all moving objects must be moved by something else. He elevated this principle to the status of a logical certainty and then used it to explain other kinds of motion. He even thought that it successfully proved the existence of God. If the universe as a whole is full of movement, he argued, it requires an exterior unmoved mover to keep it going. But of course, Aristotle observed only a specific instance that was not generally applicable. We now know that objects do not stop when there is no force on them. They tend to keep going in a straight line, a principle enshrined as Newton’s First Law.

Other observations led Aristotle to decree it certain that a vacuum can never exist, that heavy objects fall faster than light ones, and that the earth must occupy the center of the universe. All were wrong. Aristotle, alas, was mistaken on nearly all his claims about physics, not because he was a fool but because he was practicing a natural philosophy that could never lead to true theories.

To give another example: Premodern medicine was an unmitigated disaster, far more likely to kill patients than to cure them. Treatments such as bleeding and purging could only weaken the constitution of the sick, reducing their bodies’ capacity to fight off infection. Given the ineffectiveness of learned physicians, it’s little wonder that people put so much stock in miracles and magic. Perhaps the most surprising thing is that doctors were able to maintain their professional status through all the centuries when they could do little more than hasten their clients to the grave. It is modern medicine, modern Western medicine, that really can cure disease.

Islamic science suffered from similar drawbacks. Advances made by Muslim natural philosophers were significant but still modest. For instance, the importance of Alhazen’s investigations into the properties of light is undisputed. They were used by Roger Bacon in his writings on perspectiva and thence were integrated into the modern theory of vision developed by Johannes Kepler. Even so, Alhazen’s experimental method was limited and not carried forward by his immediate successors. Similarly, the intuition of Ibn al-Nafis in the thirteenth century concerning the circulation of blood between the heart and the lungs is deeply impressive. But there is no evidence that it influenced the rediscovery of this phenomenon by Michael Servetus and Realdo Colombo three centuries later.

Consequently, we should be skeptical about some of the claims made for Islamic science in recent television shows and books, not to mention Wikipedia. Unfortunately, the misattribution of scientific advances to Islamic sources has sometimes been the fault of the very pioneers who discovered them. Alchemy is a case in point. During the Middle Ages, Christian alchemists would write their treatises under the name of the fabled Arab savant Geber. Later historians mistakenly assigned developments such as the first production of powerful acids as well as the isolation of alcohol to Geber himself. Alcohol was even assigned an Arabic name by Christian authors. We now know that Geber probably did not write any of the works attributed to him.

There was one towering exception to the rule that early science tended to fail. Both the Greeks and Arabs excelled in mathematics. This was because pure rationalism works a treat when it is restricted to geometry and arithmetic. The imams had plenty of uses for math as well: The Muslim calendar follows the lunar, not the solar year, and mosques had to be oriented toward Mecca. Both these religious problems required mathematical solutions. It’s said that the complicated rules of Islamic inheritance made algebra indispensable. Even our word algebra is a corruption of al-jabr , the name of an Arabic textbook widely used by Christians.

With the exception of mathematics, in medieval Europe things were different. Aristotle’s faulty method was struck down by the Catholic Church, allowing previously forbidden ideas to flourish. The Church also made natural philosophy a compulsory part of the courses it required trainee theologians to follow. So, science held a central place in Christian centers of learning that it did not hold in Islamic madrassas. And Christianity itself provided a worldview especially compatible with experimental science.

In 1085, the great Islamic city of Toledo fell to Alfonso IV, king of Castile. Christian forces captured the magnificent library 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 mathematics.

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 be reinstated. So, after a decent interval, the pope rescinded the ban and Aristotle took his place at the heart of Christian education.

As we can see, 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 generate results deductively, Aristotle made them seem logically necessary. His admirers did not just claim that he was right; they said he had to be right. God himself was bound by what Aristotle thought because medieval theologians agreed that, though omnipotent, 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 interested primarily 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, that 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 founded the work of Copernicus and Galileo. Let me give a few examples.

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 first developed the arguments, 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 on 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 from 1543, 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 spurious 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 only would 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 were 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. The earth, bowman, and arrow are all rotating together. Galileo covers these thought experiments in great detail 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 in fact discovered in the fourteenth century at Merton College, Oxford. 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.

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.

Even in the face of today’s perceptions of a conflict between science and religion, Christianity has proved to be uniquely accommodating to the scientific study of nature. First, 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 preexisting material that resisted his purposes. This meant 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 he had ordained. The order of nature followed these laws. God was not personally manipulating each atom. By the twelfth century, William of Conches had already realized this. “I take nothing away from God,” he wrote. “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.”

Second, the Christian God is reliable. He is not capricious like the Olympians of ancient Greece or entirely beyond human comprehension like Allah. Natural philosophers (scientists, in our terms) 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. As Thierry of Chartres, another theologian of the twelfth century, put it:

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.

Third, Christianity made science a theologically justified and even righteous path to pursue. Since God created the world, exploring how it works honors its Creator. And because science studies the ordinary course of nature, it is not necessary to worry about the rare occasions when God does intervene directly through miracles. As 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 through rational analysis alone. The only way to discover his plan was to go out and look. Science could not rely on pure reason to generate theories, still less on Aristotle’s “logically necessary” conclusions. God created the world in the way he wished to, not the way Aristotle said he had to.

Given the advantages Christianity provided, it is hardly surprising that modern science developed only in the West, within a Christian civilization. Although other religious traditions could have provided a similarly fertile metaphysical ground for the study of nature, none actually did so. Christianity was a crucial cause of the unique development of Western science, the only science that has consistently produced true theories of nature.

James Hannam is the author of The Genesis of Science: How the Christian Middle Ages Launched the Scientific Revolution (Regnery), which was shortlisted for the Royal Society Science Book Prize.