Descartes' Bones by Russell Shorto

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 in 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.
    After Desgabets left Paris, he toured Benedictine abbeys in the countryside to spread the gospel of Cartesianism. Desgabets eventually published a text whose title spelled out the central matter pretty clearly:
Considerations on the present state of the controversy touching the Very Holy Sacrament of the host, in which is treated in a few words the opinion which teaches that the matter of the bread is changed into that of the body of Jesus Christ by its substantial union to his soul and to his divine person.
Together with his other activities, this little text got Desgabets branded as a heretic, with the result that his work was suppressed and his name largely forgotten by history. Meanwhile, Father Mesland, for his persistence in pursuing the question, was eventually banished to Canada.
    This then was the climate of increasing danger in which the Cartesians operated. Still, some—Rohault among