The visitors to les mercredis, as these weekly happenings became known, included some of the most famous names of the century, among them France’s supreme playwright, Molière, the socialite Madame de Sévigné, and the Dutch polymath Christiaan Huygens, who invented the pendulum clock, discovered celestial bodies, and helped develop calculus. They all came to see Rohault, a physicist who was known as the greatest living Cartesian. This description in itself suggests the gulf between that time and ours. Today, or twenty years ago, or a century ago, a student of philosophy learned about Descartes as a philosopher, a man who refashioned the landscape of the mind. For the generation that succeeded him, Descartes was that, but he was also an investigator of nature, and, for these men and women, the two things were intricately connected.
In 1667, Rohault was forty-seven years old, built like a bulldog, with a personality to match. He could be short to the point of irascible with those who failed to grasp a principle he had repeatedly tried to explain. At least part of the shortness came as a byproduct of zeal. His devotion to the master was such that he had married into the circle of Cartesians. His wife was the daughter of Claude Clerselier, caretaker of Descartes’ writings (many of which were as yet unpublished). Like Descartes himself, Rohault was intoxicated with the new means of comprehending the physical world and seemed to believe that any observation, any datum, from whatever field of inquiry, was liable to tip the balance from ignorance toward knowledge and mastery. He had made himself an authority on astronomy, geography, and anatomy. He wrote a detailed commentary on Euclid’s geometry and how to put its principles to work; his Traité de physique remained a standard textbook on physics for decades. And he didn’t restrict himself to the scholarly realm but roamed the alleys of Paris in which various craftsmen practiced their trades, watching them build clocks and distill brandy, querying them, trolling for notions and clues and methods.
This combination of intellect, acute observation, and missionary fervor came together in Rohault’s weekly demonstrations. There was an element of performance involved, and no doubt some of those who came did so for the show. Colored flames, bubbles, explosions: Cartesianism had become a spectacle. It was also rumored to offer glimpses beyond the material, into the realm of the supernatural, and some were titillated by the possibility of peeking behind the screen of ordinary existence. But Rohault and most of his visitors were after something else. There was an order in nature; one could proceed from the unseen bedrock of philosophical principles—the Cartesian method—by rungs up into the realm of matter and its manipulation. His weekly event was a salon, but one in which people took notes, scribbling fast as they tried to grasp something genuinely new.
The notes taken by an anonymous lawyer who frequented the mercredis have survived. This avocat’s account of one evening gives a sense of the scope and the intensity that people from all walks of life brought to the abstract stuff of philosophy. Rohault began the lecture by discussing the two states of waking and sleep—“The first sees true,” the lawyer wrote, “the second false”—followed by a discourse on the study of dreams. In these introductory words, Rohault was asking his audience to develop perspective on the mind and its proper functioning. Then he moved into an analysis of Descartes’ reorientation of how we know. The key, he said, was the “cogito,” which gives us certainty about our individual existence. Everything else, the lawyer noted, is only “probability.” And there, in his carefully wrapping that strange and deeply modern word in quotation marks, this nameless amateur philosopher gives us a shiver of what it must have been like, sitting amid the Louis XIV coiffures and the chalk-and-vinegar aroma of face powder, to first glimpse the horizon of the modern world.
From here, Rohault moved into Descartes’ division of reality into mind and matter. Remarkable—maybe even limitless—improvements were possible in every field of endeavor, but faster coaches, stronger swords, and more sensitive lenses required a truer understanding of the physical world and how we know it.
What exactly constitutes a material object? Attempting to answer that question plunged the physicist and his audience into the depths of philosophy. “In connection with the ‘belief’ in the existence of the ‘physical being,’ ” the lawyer noted, “we seek to understand what it is that persuades us of this belief. For example, heat is not the essence of a thing, because there are cold things. Nor is coldness the essence, because there are hot things.” And: “It is neither the hardness nor the liquidity which is the essence of a thing, and for the same reason.”
Here Descartes and his followers had set themselves in opposition to the Scholastic notion of matter. According to the traditional way of thinking about these things, the sky has blueness in it, water has wetness, garlic has its odor. These perceivable qualities are embedded in the underlying substance of a thing. Rohault, in particular, found this to be faulty logic that impeded material progress. The Aristotelians, he wrote, reason that “it would be impossible for luminous or colored bodies to cause those sensations in us which we feel, if there were not in them something very like what they cause us to feel, for, they say, nothing can give what it has not.” Rohault dismantles this logic with a simple example: the fact that a needle poked into the skin causes pain clearly does not mean that the pain is somehow in the needle. The pain is in the mind. And so, in some sense, is the blueness of the sky, the wetness of the water, the smell of the garlic. This is the root of what Descartes bequeathed not only to his immediate disciples but to most of the rest of us who came after. There is a divide in the universe—there are two distinct substances. One is matter. The other is mind. Reality is not “that out there” but a dance involving the sensor and the sensed.
Abstract as this all is, the notion was of the essence for the Cartesians. Strange to say, it was also dangerous. These conceptual, seemingly otherworldly notions had political import. As much as the Cartesians themselves wished it were not so, Cartesianism threatened certain centers of worldly power. As they met at Rohault’s mercredis and other, sometimes fancifully named Cartesian salons in Paris and around Europe (the Société des lanternistes in Toulouse, for example, took its name from the torches its members carried to light their way to its evening sessions), these men and women were acutely aware of doing so under a threat, which eased and intensified as various church and state officials modified their understanding of the new philosophy. In the case of each institution, the fear was of having its power undermined. If this new sect, Cartesianism, professed to be able to show, for example, that the body was a kind of machine and death was an absolute barrier, then where did that leave the doctrine of the afterlife or of Christ’s bodily resurrection? If miracles could be authoritatively dismissed as nonsense, a faith built upon the miraculous was groundless. For an autocratic government the threat was equally serious. While Rohault was giving physics demonstrations in Paris, in Amsterdam Baruch Spinoza—also picking up where Descartes left off—was using reason as the base from which to argue that democracy, not absolute monarchy, was the only just form of government. Such ideas were whispered in Cartesian circles, leaving rulers around Europe to view those circles as suspect, if not treasonous.
All of these fears became concentrated in a single issue. It wove one of the most abstract and seemingly unworldly elements of Cartesian philosophy into individual human life, society, and worldly power. This issue was perhaps the biggest source of anxiety that Descartes himself had for his philosophy. As for the Cartesians who sat in their salons watching demonstrations of the “magic lantern” (a forerunner of the slide projector and the cinema) and witnessing experiments involving mercury, magnetism, and barometric pressure, it gave them palpable fear of a very real-world kind: of soldiers appearing at the door to lead them away. The issue concerned the truth of the Catholic sacrament of Communion.
A notion had first struck Descartes in 1630, in a seemingly innocuous way, when he was thinking about optics and color. When you break open a loaf of bread, the inside is so very white. Surely that whiteness
is in the bread itself, is it not? From this mundane hook his mind wove a chain of logic that threatened the major institutions of Europe. Descartes himself would rather not have explored it further, but in 1643 he received a letter from one of the teachers at his old college of La Flèche. Père Denis Mesland had become a devotee of Descartes’, and he now had some questions. In the seventeenth century, as now, the central rite of Catholicism was the Mass, and the center of the Mass—the essence of the faith—was Holy Communion, in which celebrants receive bread and/or wine: the “body and blood” of Jesus Christ. One of the chief differences between Catholicism and Protestantism—one of the spurs behind the century of bloodshed that was just then ending—involved the meaning of the quotation marks in the previous sentence. Protestants (some of them, anyway) came to hold that the bread and wine represented Christ’s body and blood, whereas for Catholics mere symbolism did not get at the genuine nature of the sacred mystery involved. In Catholic theology (and in Catholic conviction, in the seventeenth century and now), when a priest repeats during the Mass the words Jesus spoke at the Last Supper—“This is my body . . . this is the cup of my blood”—he initiates a real conversion of substance. A century before Mesland’s letter, the Council of Trent, which formed in reaction to the Protestant Reformation, had decreed that, regarding the consecrated bread and wine, “our Lord Jesus Christ, true God and man, is truly, really, and substantially contained under the species of those sensible things.”
For the church, Christ was, and had to be, “really, truly, and substantially” present in the bread and wine. Intelligent, reasoning Catholics need not necessarily have a problem with the logic in this, thanks to their belief in mystery as a real force in the world. Indeed, the transformation could not be explained by ordinary means; this was part of the essence of the faith, just as the bodily resurrection and ascension to heaven were elements of the mysterious truth of Jesus’ sojourn. As for how it was that the bread, after the priest had performed the ritual of consecration, still looked like bread and felt like bread and tasted like bread, Catholic theologians had worked it out using Aristotelian categories as adapted by Thomas Aquinas. A material object, in Aristotelian science, is comprised of accidents—color, odor, taste—and substance, the real underlying thing itself. When a priest blesses bread and wine during the Mass and repeats the biblical formula, the transformation happens at the level of substance. The underlying substances of the bread and wine are swapped for the substances of the flesh and blood of Jesus Christ. Thus the term transubstantiation, which came into use by theologians around AD 1100. But the accidents of the bread and wine—which give them their appearance but which are actual components of the bread and wine—are left unchanged. This seemingly problematic bit of reality was in fact held to be a second miracle, and in the Middle Ages “proof” of the twin miracles of transubstantiation occasionally manifested itself in the world. The American philosopher Richard Watson, in writing about the Aristotelian explanation, likened the notion of accidents miraculously keeping up a faux appearance to a “shield” that covers the real substance and added, “Numerous stories were known of the shield having been dropped, so that the priest saw lying in his hand an actual piece of flesh or, more spectacularly, a tiny, perfectly formed baby.”
As far as Catholic authorities were concerned, the physics of transubstantiation had to be explained in this way. It is difficult to overestimate the multifaceted importance of the Eucharist (to give the sacrament of Communion its proper name) in Catholic Europe in the seventeenth century. Because the host actually becomes Christ’s body, it has incorporated into it Christ’s bodily pain, his willingness to suffer and die for humanity, and thus his love for humanity. Consuming the host is an act of recommitment to the faith, participation in his suffering, and acceptance of his divine love. To eat the bread is also to unite one’s own physical body with Christ’s—to become part of the body of Christ, meaning both his physical body and the body of believers. In this way, the ritual of the Eucharist was, and remains, the very essence of Catholic Christianity, tying the esoterica of faith to the essential fact of humanity: our physical, flesh-and-blood selves. Again, the point is that the act isn’t symbolic but real. The Catholic host brings what Christians believe to be the historical root of the faith—that, in Jesus, God became flesh and suffered physically and died—into the here and now, over and over, every time the Mass is celebrated.
As spiritually meaningful as this concept was, it also had tremendous implications for real-world power. The whole infrastructure of the church—parishes and cathedrals, priests and nuns, real estate, art, revenue, the ability to mold and manipulate heads of state—rested on it. Only an ordained priest could say Mass, and in celebrating Communion, repeating the words “This is my body,” the priest took on the personage of Christ and became the indispensable vehicle through which Catholics participated in the mystery of Christ’s bodily suffering and death and resurrection. Because the host was the real substance of the body of Christ, the church had what it believed to be the franchise on salvation. The Protestant Reformation represented an assault on transubstantiation and the real-world power it gave the Catholic Church. Father Mesland was among the first to recognize that Cartesian science was another such assault. In Descartes’ reckoning of the universe there was no “real” apple or tree or butterfly lurking beneath the shield of accidental appearances of these entities. If the object in question was hard, gray, and flecked and otherwise gave every appearance of being a piece of granite, then it was a piece of granite. And if it looked, smelled, and tasted like bread, it was . . . bread. That was the direction Mesland saw Descartes’ ideas heading, and it was a dangerous one.
Descartes responded with an assurance that his philosophy did not deny the genuine presence of Christ in the host. In fact, he believed he offered a philosophically satisfactory account of it, one that could coexist with the mechanistic view of nature. Indeed, by stressing a dualistic view of reality, by putting the ephemeral stuff of mind and soul in one category and the physical world in another, he believed he was building a wall around the fortress of faith, protecting it from the encroachments of science. At the same time, he was hoping to protect investigations of the natural world from theological interference. He had been shaken by church condemnations of scientists, particularly of Galileo (“I was so surprised by this that I nearly decided to burn all my papers, or at least let no one see them,” he wrote on learning of Galileo’s conviction for publishing his heliocentric views). Descartes himself was so devout in his faith yet so certain of the legitimacy of reason-based investigations of the natural world that the division of reality into two distinct halves seemed the only logical conclusion.
While the goal was in part to protect religion, one long-term effect of Cartesian dualism—as it seeped into Western consciousness over the ensuing decades and centuries—was to drastically limit religion’s scope. In the prevailing modern view, faith has no business meddling in astronomy or biology. And the logical extension of this thinking has been the very modern stance of atheism. To some extent, such an outcome was foreseen by critics of Descartes’ own time, who saw his work and that of other mechanistically inclined philosophers as giving reason full sway over human reality and relegating faith to superstition. This was surely not Descartes’ intention, nor was it the intention of his contemporaries. Descartes’ lifelong timidity in confronting church authorities was always at odds with his ambition, and in the matter of the Eucharist he hoped to have it both ways: to lay a new foundation not only for physics but for Christian theology. He pushed Mesland, and other of his followers, to take up the challenge and bring the church’s explanation of transubstantiation in line with science—that is to say, Cartesianism. Again, his immodest goal was to replace Aristotle completely as the base of all knowledge.
Descartes himself avoided direct attack over the Eucharist, but from the time of his death the matter expanded into a full-fledged controversy. His followers took up the challenge i
n various ways. Descartes had tried to override the whole mechanism of the Aristotelian explanation, arguing that it was a mistake to talk about transformation of substance, that instead the miracle involved the union of Christ’s soul with the bread. In this way, there was no need for a second miracle, in which the “shield” of breadlike appearance covers the underlying substance. This explanation itself caused alarm, since it seemed only a slight variation on Protestant ideas that the host symbolized Christ’s body. For the church, the soul of Christ was apparently not substantial enough to support its worldly edifice; Catholic authorities needed the body, too.
Nevertheless, the Cartesians pushed their arguments. Rohault offered a defense of the Cartesian view of the Eucharist. Claude Clerselier, Rohault’s father-in-law, wisely refrained from including the exchange of letters between Descartes and Mesland in his publication of Descartes’ correspondence, but he sent copies to influential parties. Robert Desgabets, a Benedictine monk with a penchant for science who had never met Descartes but had become entranced by his philosophy, was one of the recipients of the letters. Desgabets journeyed to Paris to join Cartesian salons, and—rather dramatically demonstrating the close link the Cartesians saw between philosophy and medicine—lectured on how one might perform a blood transfusion while also offering his own support for a Cartesian view of transubstantiation.
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