To Explain the World: The Discovery of Modern Science (19 page)

The pace of translation accelerated in the twelfth century. At the century’s start, an Englishman, Adelard of Bath, traveled extensively in Arab countries; translated works of al-Khwarizmi; and, in
Natural Questions
, reported on Arab learning. Somehow Thierry of Chartres learned of the use of zero in Arab mathematics, and introduced it into Europe. Probably the most important twelfth-century translator was Gerard of Cremona. He worked in Toledo, which had been the capital of Christian Spain before the Arab conquests, and though reconquered by Castilians in 1085 remained a center of Arab and Jewish culture. His Latin translation from Arabic of Ptolemy’s
Almagest
made Greek astronomy available to medieval Europe. Gerard also translated Euclid’s
Elements
and works by Archimedes, al-Razi, al-Ferghani, Galen, Ibn Sina, and al-Khwarizmi. After Arab Sicily fell to the
Normans in 1091, translations were also made directly from Greek to Latin, with no reliance on Arabic intermediaries.

The translations that had the greatest immediate impact were of Aristotle. It was in Toledo that the bulk of Aristotle’s work was translated from Arabic sources; for instance, there Gerard translated
On the Heavens, Physics
, and
Meteorology.

Aristotle’s works were not universally welcomed in the church. Medieval Christianity had been far more influenced by Platonism and Neoplatonism, partly through the example of Saint Augustine. Aristotle’s writings were naturalistic in a way that Plato’s were not, and his vision of a cosmos governed by laws, even laws as ill-developed as his were, presented an image of God’s hands in chains, the same image that had so disturbed al-Ghazali. The conflict over Aristotle was at least in part a conflict between two new mendicant orders: the Franciscans, or gray friars, founded in 1209, who opposed the teaching of Aristotle; and the Dominicans, or black friars, founded around 1216, who embraced “The Philosopher.”

This conflict was chiefly carried out in new European institutions of higher learning, the universities. One of the cathedral schools, at Paris, received a royal charter as a university in 1200. (There was a slightly older university at Bologna, but it specialized in law and medicine, and did not play an important role in medieval physical science.) Almost immediately, in 1210, scholars at the University of Paris were forbidden to teach the books of Aristotle on natural philosophy. Pope Gregory IX in 1231 called for Aristotle’s works to be expurgated, so that the useful parts could be safely taught.

The ban on Aristotle was not universal. His works were taught at the University of Toulouse from its founding in 1229. At Paris the total ban on Aristotle was lifted in 1234, and in subsequent decades the study of Aristotle became the center of education there. This was largely the work of two thirteenth-century clerics: Albertus Magnus and Thomas Aquinas. In the fashion of the times, they were given grand doctoral titles: Albertus was the “Universal Doctor,” and Thomas the “Angelic Doctor.”

Albertus Magnus studied in Padua and Cologne, became a Dominican friar, and in 1241 went to Paris, where from 1245 to 1248 he occupied a professorial chair for foreign savants. Later he moved to Cologne, where he founded its university. Albertus was a moderate Aristotelian who favored the Ptolemaic system over Aristotle’s homocentric spheres but was concerned about its conflict with Aristotle’s physics. He speculated that the Milky Way consists of many stars and (contrary to Aristotle) that the markings on the Moon are intrinsic imperfections. The example of Albertus was followed a little later by another German Dominican, Dietrich of Freiburg, who independently duplicated some of al-Farisi’s work on the rainbow. In 1941 the Vatican declared Albertus the patron saint of all scientists.

Thomas Aquinas was born a member of the minor nobility of southern Italy. After his education at the monastery of Monte Cassino and the University of Naples, he disappointed his family’s hopes that he would become the abbot of a rich monastery; instead, like Albertus Magnus, he became a Dominican friar. Thomas went to Paris and Cologne, where he studied under Albertus. He then returned to Paris, and served as professor at the university in 1256–1259 and 1269–1272.

The great work of Aquinas was the
Summa Theologica
, a comprehensive fusion of Aristotelian philosophy and Christian theology. In it, he took a middle ground between extreme Aristotelians, known as Averroists after Ibn Rushd; and the extreme anti-Aristotelians, such as members of the newly founded Augustinian order of friars. Aquinas strenuously opposed a doctrine that was widely (but probably unjustly) attributed to thirteenth-century Averroists like Siger of Brabant and Boethius of Dacia. According to this doctrine, it is possible to hold opinions true in philosophy, such as the eternity of matter or the impossibility of the resurrection of the dead, while acknowledging that they are false in religion. For Aquinas, there could be only one truth. In astronomy, Aquinas leaned toward Aristotle’s homocentric theory of the planets, arguing that this theory was founded on reason while Ptolemaic theory merely agreed with
observation, and another hypothesis might also fit the data. On the other hand, Aquinas disagreed with Aristotle on the theory of motion; he argued that even in a vacuum any motion would take a finite time. It is thought that Aquinas encouraged the Latin translation of Aristotle, Archimedes, and others directly from Greek sources by his contemporary, the English Dominican William of Moerbeke. By 1255 students at Paris were being examined on their knowledge of the works of Aquinas.

But Aristotle’s troubles were not over. Starting in the 1250s, the opposition to Aristotle at Paris was forcefully led by the Franciscan Saint Bonaventure. Aristotle’s works were banned at Toulouse in 1245 by Pope Innocent IV. In 1270 the bishop of Paris, Étienne Tempier, banned the teaching of 13 Aristotelian propositions. Pope John XXI ordered Tempier to look further into the matter, and in 1277 Tempier condemned 219 doctrines of Aristotle or Aquinas.
³
The condemnation was extended to England by Robert Kilwardy, the archbishop of Canterbury, and renewed in 1284 by his successor, John Pecham.

The propositions condemned in 1277 can be divided according to the reasons for their condemnation. Some presented a direct conflict with scripture—for instance, propositions that state the eternity of the world:

  9.  That there was no first man, nor will there be a last; on the contrary, there always was and always will be the generation of man from man.

 87. That the world is eternal as to all the species contained in it; and that time is eternal, as are motion, matter, agent, and recipient.

Some of the condemned doctrines described methods of learning truth that challenged religious authority, for instance:

 38. That nothing should be believed unless it is self-evident or could be asserted from things that are self-evident.

150. That on any question, a man ought not to be satisfied with certitude based upon authority.

153. That nothing is known better because of knowing theology.

Finally, some of the condemned propositions had raised the same issue that had concerned al-Ghazali, that philosophical and scientific reasoning seems to limit the freedom of God, for example:

 34. That the first cause could not make several worlds.

 49. That God could not move the heavens with rectilinear motion, and the reason is that a vacuum would remain.

141. That God cannot make an accident exist without a subject nor make more [than three] dimensions exist simultaneously.

The condemnation of propositions of Aristotle and Aquinas did not last. Under the authority of a new pope who had been educated by Dominicans, John XXII, Thomas Aquinas was canonized in 1323. In 1325 the condemnation was rescinded by the bishop of Paris, who decreed: “We wholly annul the aforementioned condemnation of articles and judgments of excommunication as they touch, or are said to touch, the teaching of blessed Thomas, mentioned above, and because of this we neither approve nor disapprove of these articles, but leave them for free scholastic discussion.”
⁴
In 1341 masters of arts at the University of Paris were required to swear they would teach “the system of Aristotle and his commentator Averroes, and of the other ancient commentators and expositors of the said Aristotle, except in those cases that are contrary to the faith.”
⁵

Historians disagree about the importance for the future of science of this episode of condemnation and rehabilitation. There are two questions here: What would have been the effect on science if the condemnation had not been rescinded? And what would have been the effect on science if there had never been any condemnation of the teachings of Aristotle and Aquinas?

It seems to me that the effect on science of the condemnation
if not rescinded would have been disastrous. This is not because of the importance of Aristotle’s conclusions about nature. Most of them were wrong, anyway. Contrary to Aristotle, there was a time before there were any men; there certainly are many planetary systems, and there may be many big bangs; things in the heavens can and often do move in straight lines; there is nothing impossible about a vacuum; and in modern string theories there are more than three dimensions, with the extra dimensions unobserved because they are tightly curled up. The danger in the condemnation came from the
reasons
why propositions were condemned, not from the denial of the propositions themselves.

Even though Aristotle was wrong about the laws of nature, it was important to believe that there
are
laws of nature. If the condemnation of generalizations about nature like propositions 34, 49, and 141, on the ground that God can do anything, had been allowed to stand, then Christian Europe might have lapsed into the sort of occasionalism urged on Islam by al-Ghazali.

Also, the condemnation of articles that questioned religious authority (such as articles 38, 150, and 153 quoted above) was in part an episode in the conflict between the faculties of liberal arts and theology in medieval universities. Theology had a distinctly higher status; its study led to a degree of doctor of theology, while liberal arts faculties could confer no degree higher than master of arts. (Academic processions were headed by doctors of theology, law, and medicine in that order, followed by the masters of arts.) Lifting the condemnation did not give the liberal arts equal status with theology, but it helped to free the liberal arts faculties from intellectual control by their theological colleagues.

It is harder to judge what would have been the effect if the condemnations had never occurred. As we will see, the authority of Aristotle on matters of physics and astronomy was increasingly challenged at Paris and Oxford in the fourteenth century, though sometimes new ideas had to be camouflaged as being merely
secundum imaginationem
—that is, something imagined, rather than asserted. Would challenges to Aristotle have been possible if his authority had not been weakened by the
condemnations of the thirteenth century? David Lindberg
⁶
cites the example of Nicole Oresme (about whom more later), who in 1377 argued that it is permissible to imagine that the Earth moves in a straight line through infinite space, because “To say the contrary is to maintain an article condemned in Paris.”
⁷
Perhaps the course of events in the thirteenth century can be summarized by saying that the condemnation saved science from dogmatic Aristotelianism, while the lifting of the condemnation saved science from dogmatic Christianity.

After the era of translation and the conflict over the reception of Aristotle, creative scientific work began at last in Europe in the fourteenth century. The leading figure was Jean Buridan, a Frenchman born in 1296 near Arras, who spent much of his life in Paris. Buridan was a cleric, but secular—that is, not a member of any religious order. In philosophy he was a nominalist, who believed in the reality of individual things, not of classes of things. Twice Buridan was honored by election as rector of the University of Paris, in 1328 and 1340.

Buridan was an empiricist, who rejected the logical necessity of scientific principles: “These principles are not immediately evident; indeed, we may be in doubt concerning them for a long time. But they are called principles because they are indemonstrable, and cannot be deduced from other premises nor be proved by any formal procedure, but they are accepted because they have been observed to be true in many instances and to be false in none.”
⁸

Understanding this was essential for the future of science, and not so easy. The old impossible Platonic goal of a purely deductive natural science stood in the way of progress that could be based only on careful analysis of careful observation. Even today one sometimes encounters confusion about this. For instance, the psychologist Jean Piaget
⁹
thought he had detected signs that children have an innate understanding of relativity, which they lose later in life, as if relativity were somehow logically or philosophically necessary, rather than a conclusion ultimately based on observations of things that travel at or near the speed of light.

Though an empiricist, Buridan was not an experimentalist. Like Aristotle’s, his reasoning was based on everyday observation, but he was more cautious than Aristotle in reaching broad conclusions. For instance, Buridan confronted an old problem of Aristotle: why a projectile thrown horizontally or upward does not immediately start what was supposed to be its natural motion, straight downward, when it leaves the hand. On several grounds, Buridan rejected Aristotle’s explanation that the projectile continues for a while to be carried by the air. First, the air must resist rather than assist motion, since it must be divided apart for a solid body to penetrate it. Further, why does the air move, when the hand that threw the projectile stops moving? Also, a lance that is pointed in back moves through the air as well as or better than one that has a broad rear on which the air can push.