François-Marie Arouet, a.k.a Voltaire, and Denis Diderot.

In mid-December 1776, the eighty-three-year-old Voltaire pulled out a piece of paper and dashed off a note to Diderot. Having been exiled from Paris for more than twenty-five years, the now wizened and virtually toothless philosophe lamented the fact that the two men had never laid eyes on each other: “I am heartbroken to die without having met you … I would gladly come and spend my last fifteen minutes in Paris in order to have the solace of hearing your voice.”

Fifteen months later, Voltaire rolled into the capital in his blue, star-spangled coach. Quite ill with prostate cancer, the famous humanitarian, essayist, and playwright nonetheless organized a feverish schedule for himself. In addition to finishing work on a five-act tragedy—he lived long enough to attend the premiere—Voltaire spent most of his days holding court in a friend’s hôtel particulier on the corner of the rue de Beaune and the quai des Théatins. Here, for hours at a time, Voltaire received visits from a long list of adoring friends and dignitaries, among them Benjamin Franklin and his son. Sometime during Voltaire’s three-month stay, Diderot also came to pay his respects. Journalists who wrote about the meeting hinted that some relationships are best conducted solely by correspondence.

Diderot and Voltaire had first exchanged letters in 1749 when the “prince of the philosophes” had invited the then up-and-coming Diderot to dinner. In addition to hoping to get to know the clever author of the Letter on the Blind, Voltaire had presumably hoped to help the newly appointed editor of the Encyclopédie rethink his atheism. Diderot decided to dodge both the invitation and the sermon. One might wonder what kind of young writer turns down lunch with the most famous public intellectual ever to live. The answer, in 1749, was pretty clear: a proud and unremorseful unbeliever who had no interest in having his philosophy questioned by an unbending deist. 

The two philosophes nonetheless remained in contact (from afar) over the course of the next twenty-eight years. Voltaire sent fifteen more letters. Diderot replied nine times. The relationship, which actually deepened as time went by, was cemented by mutual friends, mutual interests, and a deep reciprocal respect for each other’s intelligence. And yet, well into the 1760s, a continued sense of wariness existed on both sides. In addition to their divergent views on religion—Voltaire remained a Newtonian deist whereas Diderot had long declared himself an unbeliever—the two men evidently had ambivalent feelings about each other’s respective literary careers. Both had invested heavily in the theater, and each also believed that the other was on the wrong path. Voltaire, from Diderot’s point of view, continued to churn out an endless string of rearguard classical dramas and comedies; as for Voltaire, he secretly found Diderot’s bourgeois dramas to be a sad testament to the direction of the theater.

What did these two old men talk about when they finally sat in front of each other in 1778? The battles they had waged, won, and lost? The dark days of the Encyclopédie, when Voltaire repeatedly tried to convince both Diderot and d’Alembert to drop the project? The friends who had died over the years, especially the beloved Damilaville? Voltaire’s failed attempt to get Diderot elected to the Académie française? Their mutual friend Catherine the Great? Diderot’s curious book on Seneca? His secret contributions to Raynal? Or how much Diderot was in deep admiration for Voltaire’s defense of the family of the Protestant Jean Calas, who had been falsely accused of killing his son after he converted to Catholicism?

The only real accounts we have, alas, focus on an argument that the two men had regarding the merits of Shakespeare. Convinced of the superiority not only of French theater but of his own art, Voltaire supposedly asked Diderot how it was possible to “prefer this tasteless monster to Racine or Virgil.” In the discussion that ensued, Diderot conceded that the playwright lacked the polish of some of the greatest poets, but that the Englishman nonetheless possessed a sublime energy that transcended the “gothic” aspects of his writing. He then went on to compare Shakespeare to the massive fifteenth-century statue of Saint Christopher that stood just outside the doors leading into Notre Dame Cathedral. While perhaps crude and rustic, this colossus was very much like Shakespeare, according to Diderot, because “the greatest men still walk through his legs without the top of their head touching his testicles.” The implication was clear. Voltaire, who rightly considered himself the greatest French poet and playwright of his generation, did not measure up either. According to one journalist’s account of this exchange, Voltaire was not “excessively happy with Monsieur Diderot” after this comment.

Diderot’s unrestrained tongue had reportedly irked Voltaire as much as it had captivated him. After years of exchanging letters—with Diderot, the epistolary mode had the distinct advantage of allowing the other person to respond without being interrupted—Voltaire had finally witnessed the Encyclopedist’s legendary ability to leap from one idea to the next without stopping to take a breath. After Diderot left the quai des Théatins, Voltaire reportedly remarked to some friends that his visitor had lived up to his reputation as a tremendous wit, but that nature had refused him “an essential talent, that of true conversation.” Diderot, too, summed up his meeting with the brilliant yet failing Voltaire. He reported that the man was like an ancient “enchanted castle whose various parts are falling apart,” but whose corridors were “still inhabited by an old sorcerer.”

Diderot’s visit with Voltaire was the first and last time that these two figureheads of the Enlightenment era would see each other in person. Not long after his visit, on May 30, the old sorcerer succumbed to his cancer. This turned out to be the first of two significant deaths in 1778. A little more than a month later, on July 2, Jean-Jacques Rousseau would die as well. The story told throughout Paris was that Rousseau had felt ill after taking a morning stroll through the gardens at the château d’Ermenonville, twenty-five miles north of Paris. Upon returning to the cottage where he was staying, he nervously informed his longtime companion, Thérèse Levasseur, that he had a stabbing pain in his chest, a strange tingling sensation on the soles of his feet, and a ferociously throbbing headache. Soon thereafter, the Citizen of Geneva collapsed and died.

Rousseau’s and Voltaire’s deaths signaled the beginning of an era in which many more of Diderot’s close friends, associates, and enemies would also die. By 1783, all the main players with whom he had worked on the Encyclopédie—this included d’Alembert, Jaucourt, and the project’s four printers including André-François Le Breton—were gone. This ever-expanding necrology also came to include Madame d’Épinay and several of his painter friends as well, among them Jean-Baptiste Chardin and Louis-Michel van Loo. Diderot’s generation was disappearing.

Andrew S. Curran is the William Armstrong Professor of the Humanities at Wesleyan University. His major publications include Diderot and the Art of Thinking Freely; the article “Faces of Monstrosity in Eighteenth-Century Thought” in Eighteenth-Century Life; and two books: Sublime Disorder: Physical Monstrosity in Diderot’s Universe and The Anatomy of Blackness: Science and Slavery in an Age of Enlightenment. Elected a fellow in the history of medicine at the New York Academy of Medicine in 2010, Curran has also received fellowships from the National Endowment for the Humanities, the Mellon Foundation, and the John D. and Catherine T. MacArthur Foundation. He was the cowinner of the James L. Clifford Prize for the best article in eighteenth-century studies in 2011 and received a National Endowment for the Humanities Public Scholars award in 2016.

Excerpted from Diderot and the Art of Thinking Freely, by Andrew S. Curran, published by Other Press on January 15, 2019. Copyright © Andrew S. Curran. Reprinted by permission of Other Press.