The Foundations of Modern Science in the Middle Ages
Their Religious, Institutional, and Intellectual Contexts
It is not easy to think of an aspect of medieval culture that enjoys popular acclaim today (unless we count the paternalistic medieval code of chivalry or the militaristic medieval ideal of knightly valour — do you see what I mean?), though it is a favourite pastime to tabulate all the many ways in which medieval society was thoroughly awful. Perhaps no aspect of medieval culture is more eagerly and easily derided than its science: impotent, absurd, hide-bound, airy, and wrong. It is a cunning strategy from our point of view, of course, for what better grounds on which to criticize others than those on which we stand most confidently? The bad reputation of medieval science dates from the seventeenth century, and is perhaps exemplified most famously in Galileo’s character (in his Dialogue) Simplicio, a dim-witted Aristotelian whose flounderings serve as a foil for the boldness and intelligence of the new scientists — and, in particular, of Galileo himself.
Fair enough, I suppose. The old order, which certainly merited criticism, was also open to caricature. Today, however, from a distance of several hundred years, we can look back at the dispute and try to discriminate the just criticisms from the unjust, and perhaps to trace certain threads of the fabric of the new science back into the Middle Ages, supplying the appreciation that was withheld or neglected at the time.
This is very much the objective of Edward Grant’s fine book, a study of the debt which modern science owes to medieval Europe. Grant is a leading scholar in medieval science, and has published numerous books on various aspects of the subject; this book feels like a condensation and summation of a lifetime of learning. Its conclusions, as is fitting, are balanced: there were important elements of the new science, he argues, that were genuinely new and which were not anticipated by medieval thinkers, but, at the same time, there were real and significant respects in which the medieval period made the birth of the new science possible.
To the extent that the new science was stimulated by encounters with Greek science, the Middle Ages deserves credit for having made the Greek texts available in a language that Europeans could understand. When knowledge of Greek was largely lost in the later Roman Empire, the scientific texts were preserved by Eastern Christians — whether Orthodox or Nestorian — and were then translated into Arabic in the aftermath of the Islamic conquests. Through the eleventh and twelfth centuries these texts found their way back to Europe, and from Arabic to Latin, through a dedicated and far-sighted translation effort, centred on the Iberian peninsula. They were eagerly taken up for study in the universities, as is well known.
The universities themselves deserve comment. We are sometimes inclined to take universities for granted, but it is well to consider what a rare and, in some respects, peculiar institution a university is. Apart from distant and singular Greek models like the Academy and Lyceum, there was really no precedent for the medieval university. Medieval scholars were self-consciously aware that the institution was not intended to serve the practical needs of society. There was a strong emphasis, which will come as no surprise to those familiar with medieval ideas about the liberal arts and the relative merits of the contemplative and active life, that the university was grounded in a love of learning and an appreciation for the intrinsic value of knowledge. The university enjoyed a wide liberty for free inquiry; interventions by civil and ecclesiastical authorities were remarkably rare. Its curriculum was structured around the trivium (grammar, rhetoric, logic) and the quadrivium (arithmetic, geometry, astronomy, music). It is significant, for our present considerations, that the quadrivium had a significant mathematical component, for we all know how important mathematics was, and is, to the natural sciences.
A third important factor that prepared the ground for science was the emergence, within the universities, of men well-trained in both natural philosophy and theology. Theology was the highest field of study, the ‘queen of the sciences’, and one could gain entry to a program of theological study only after having obtained a thorough grounding in more elementary subjects, including philosophy. The fact that theologians had, as a matter of course, also studied natural philosophy meant that there was no artificial bifurcation between the two fields of study, and certainly no motive for hostility; rather, the theologian-natural philosophers were able to relate the two fields of study to one another with relative ease. The interest they took in natural philosophy was often, naturally enough, from a theological vantage point — as a means to better understand and interpret Scripture, for instance — but that does not alter the essential point, which is that there was a group of elite scholars in Europe who understood and valued natural philosophy.
Those, then, are several historical and contextual factors that, Grant argues, created a climate in which interest in scientific questions could flourish. But were there any specific medieval intellectual contributions to the sciences themselves? Grant argues that medieval science was divisible into two parts: natural philosophy, concerned with the principles of nature at a fairly general level, and the exact sciences, such as optics or statics, in which specific scientific questions were addressed. The medieval contribution was principally to the former; scholars of the period mastered the ancient methods of the exact sciences, but did not add substantially to them.
In the light of that fact — which might reasonably be considered a failure — it is worthwhile to pause briefly to consider several of the most common criticisms of medieval science. One, of course, is that the medieval period did little to advance the exact sciences. Grant, as was just said, does not contest the charge, but argues that some allowance must be made for the difficult conditions under which medieval scholars laboured: it was a period in which, owing to the relatively small scholarly community and the mutable media available for recording and transmitting knowledge, ‘knowledge was as likely to vanish as to be preserved’. Consequently, ‘an enormous effort would have been required just to maintain the status quo’. We are, I think, sometimes too apt to forget that fact. Another common criticism of medieval science is that it was unfruitful because it was not experimental; this, again, is true to a large extent, but is the merit of an experimental approach so very evident at the outset? Grant argues that within the Aristotelian intellectual tradition which dominated the high medieval period experimental science actually seemed to be a superfluous, if not actually obstructive, endeavour. Aristotle’s physics implied that the nature of a thing would be manifest most clearly under natural conditions; to study something under ‘unnatural’, laboratory conditions, in which objects were manipulated, constrained, or otherwise tampered with, would therefore not have taught one about their true nature. Overcoming this objection required overcoming Aristotelian physics (which was, in some sense, the whole adventure of medieval science). Instead, medieval scholars preferred to argue deductively from principles. Finally, it is sometimes said that medieval scholars wasted their time with pseudo-sciences like alchemy, astrology, and divination; but this is false: these subjects were not part of the medieval curriculum. Interest in them belongs principally to the early modern period, contemporaneous with Bacon, Descartes, and Galileo.
Returning, then, to the question of whether medieval scholars made any significant concrete contributions to scientific progress, we should look to conceptual advances more than to experimental results. And we find, perhaps surprisingly, a quite wonderful litany of contributions that are so basic to us as to be almost invisible. Medieval natural philosophers argued over and clarified ideas about causality, necessity, contingency, and degrees of certitude. They studied, under Aristotle’s guidance, types of causes, and some (like John Buridan) actually anticipated the early modern philosophers by rejecting, for better or worse, final causes in nature. They developed conceptual frameworks for discussing infinities and infinitesimals, and mathematical treatments of qualities. They developed a language for describing kinematics, and proposed precise definitions for concepts such as uniform motion, uniform acceleration, and instantaneous velocity. They distinguished intensive and extensive qualities. They proposed principles of simplicity and economy of explanation. Crucially, they adopted the concept of ‘the common course of nature’, which granted to the natural world an integrity and consistency that made it intelligible and fit for scientific scrutiny, not immune from divine intervention but nonetheless having an orderly structure of its own.
This is not to claim that their ideas about these matters were all correct; in many cases they were not. It is to claim — and it seems to me a significant point — that many of the breakthroughs in early modern science did not occur because new questions were asked, but because new answers were given to old questions. The conversation was in many respects already happening; the questions were thought worthy of study; the shelves were stacked with proposals and counter-proposals.
Among the more interesting points Grant makes about the conceptual developments in medieval natural philosophy concerns the impact of the famous, or infamous, Condemnation of 1277. This was one of the infrequent ecclesiastical interventions into the intellectual life of the university: the Bishop of Paris issued a condemnation of some 219 philosophical and theological propositions. In his book on scholasticism, Josef Pieper reflected ruefully on the chilling influence these condemnations had on the dialogue between theology and philosophy, and between theological authority and philosophical inquiry. Grant has a more positive appraisal because of the unforeseen positive impact the condemnations had on natural philosophy. The burden of several of the condemnations, in particular, had been to insist that God’s power can be limited by nothing save logical contradiction. This was an idea fraught with peril for natural philosophy, for it might have had the effect of dissolving the order of nature into radically contingent and potentially capricious ‘happenings’, its character dependent from moment to moment on the changeability of God’s omnipotent will. (Something very like this seems to have afflicted Islamic natural philosophy, and also eventually certain Christian thinkers like William of Ockham.)
Instead, however, the doctrine of God’s omnipotence had a milder and more fruitful effect: it began to loosen the stranglehold that Aristotelian physics had on the medieval imagination. The Aristotelian view of nature, however correct it was as a description of our world, was not the only way God might have structured the world he created. This thought inspired medieval natural philosophers to speculate about possible worlds that might differ in one respect or another from ours, worlds in which one or another of the principles of Aristotelian physics did not apply. They found that certain of these ‘natural impossibilities’ were logically defensible — that vacua might exist, for instance, either within or beyond our cosmos, or that other worlds might exist. The arguments Aristotle had offered in defence of his positions were therefore subjected to critique and found wanting in certain respects. This process was immensely important for the development of the sciences, for modern science could not have emerged until people took seriously the idea that Aristotelian science might be wrong.
In closing, I would like to examine a few specific technical developments of medieval science that seem particularly closely related to developments usually associated with early modern science. In particular I will briefly examine some medieval arguments about the earth’s axial rotation, about motion and kinematics, and about the concepts of inertia and momentum.
Certain medieval natural philosophers entertained the thought that the earth might rotate axially once each day. It seemed a more elegant and economical way of explaining the observed daily rotation of the celestial sphere. The principal objection to the idea, of course, is that we seem to be stationary; natural philosophers considered whether that was a sound objection. John Buridan posed the problem as one of relative motion, and he argued that if the earth was rotating an arrow shot directly upward would fall to the ground in a different spot, since the ground would have rotated some distance while it was aloft. (In other words, he did not have the concept of inertia.) Nicole Oresme, however, who was one of the greatest natural philosophers of the later Middle Ages, pointed out that if the earth was rotating then evidently the atmosphere was also rotating with it (else we would always feel a wind from the same direction), and so the arrow aloft would be carried by the air and fall to earth exactly where it was launched. This is not quite a correct explanation, but it is probably about as good as one can do without the concept of inertia. Oresme, in fact, went systematically through all of the objections to the earth’s axial rotation and found them all wanting; he therefore concluded that there was no good reason why the earth should not rotate. He had, however, no positive case to make for its actual rotation. It is interesting to note that several of his arguments reappear in the writings of Copernicus.
I have already mentioned above that medieval natural philosophers made several important conceptual contributions to kinematics. They were motivated to do so by a quite general interest in the augmentation and diminution of qualities — the increase of grace in the soul, for instance, or the reddening of leaves in the autumn, or the acceleration of a moving body. A mathematics to describe this variation in quantifiable qualities was developed, and the concepts of uniform motion and uniformly accelerated motion were articulated, principally by a group of men at Oxford’s Merton College. (They are collectively called ‘the Oxford calculators’.) Perhaps their finest achievement was a derivation of the mean speed theorem; they gave the theorem verbally, not algebraically. Nicole Oresme later gave a geometric proof that was in all essentials identical to the geometric proof given by Galileo, for whom the mean speed theorem was foundational to the new science of motion. It is possible that Galileo learned the theorem from medieval treatises, which circulated widely in Italy, but this has not actually been demonstrated.
Some interesting modifications of Aristotle were made on the topic of the dynamics of motion. Aristotle had argued that the velocity of an object was proportional to its weight and inversely proportional to the resistance to its motion (v ~ W ~ 1/R); this led, however, to infinite velocities when the resistance was zero, which was one of the reasons Aristotle offered for the impossibility of a vacuum. Thomas Bradwardine, at Oxford, suggested instead that velocity was proportional to the applied force and inversely proportional to a combination of weight and resistance (v ~ F/(W + R)). This was wrong — it is acceleration that is proportional to force — but it was interesting because it behaved nicely in a vacuum (R = 0). This allowed Bradwardine to think about the possibility of motion in a vacuum, and to propose the idea that a medium was a retarding factor imposed upon a more basic, if hypothetical, vacuum case. This was a powerful idea that was to be of central importance to Galileo and Newton. Bradwardine also argued for a somewhat different set of ideas, in which motion did not depend on weight or size, but on an intensive quality called ‘internal resistance’. This is rather similar to Galileo’s use of ‘specific weight’ in the same context in an early manuscript (De motu, c.1590), which was later supplanted by the more universal (and correct) claim that motion is independent of the constitution of an object (Two New Sciences, 1638). Again, despite the suggestive parallels, no connection between Bradwardine and Galileo has been demonstrated on this matter.
Finally, we can look briefly at early ideas related to inertia and momentum. John Buridan argued that the motion of an object which results from an impressed force was determined by the object’s ‘impetus’, which he defined as a combination of its speed and its ‘quantity of matter’. I do not know what he meant by ‘quantity of matter’, but if he meant something like ‘mass’ then his impetus would be what we call momentum. In modern physics the impressed force is equal to the time rate of change of momentum, so Buridan was not too far off. He conceived of impetus as something that would be preserved unless diminished by an outside force, which is again suggestive of the modern concept of conservation of momentum. For Buridan, however, impetus was a cause of motion, rather than simply a quantity of motion, and in this he differed sharply from the modern view. Also, despite his idea that impetus would be preserved in the absence of outside forces, he did not conceive of rest and uniform motion as comparable states, nor of the possibility of infinite uniform motion — which was, in any case, an impossibility in an Aristotelian cosmos.
In each of these examples we see something that I find quite fascinating: challenges to the Aristotelian framework and the proposal of creative ideas that bore a certain family resemblance to the ideas that became basic to physics during the sixteenth and seventeenth centuries. This supports, I think, the claim made earlier that the birth of modern science was in important respects a consequence of new answers being given to old questions. The brilliance and power of those new answers is beyond dispute, but the probity and intelligence of the questions ought also to have our respect. Grant makes a strong case for the claim that modern science could not have developed without the preparatory work — cultural, institutional, literary, and conceptual — of medieval scholars, and, as such, it seems long past time for their contributions to be acknowledged.