Voltaire, Rousseau, and Montesquieu are the names most readily associated with the 18th-century French Enlightenment. But Denis Diderot, though less well known, ultimately may have had a greater effect on the formation of the Enlightenment than any of them. Diderot’s name generally falls under the rubric of “philosophe,” never to be confused with the title “philosopher.” “In the eighteenth century,” writes James Fowler, editor of New Essays on Diderot, “the word ‘philosophe’ connoted a man of ideas but also a man of action, a would-be agent of social and political change, a champion of progress.”

This is how Denis Diderot saw himself. The author of novels, plays, philosophical dialogues, art and theatre criticism, and more, he was a literary man of all work, the intellectual par excellence. His most substantial work was that which has come to be known as the great French Encylopédie. As its chief editor over the course of a quarter of a century, Diderot saw its 17 volumes containing 71,818 articles and 11 further volumes containing 2,885 plates through to publication against the always looming threat of censorship and continuous financial struggle. Among the Encylopédie’s more than 150 contributors were D’Alembert, Helvétius, d’Holbach, Turgot, Quesnay, Rousseau, Montesquieu, Buffon, Condorcet, and Voltaire, an 18th-century all-star literary and philosophical vaudeville. Diderot himself wrote, among others, the articles “Nature,” “The Will,” “The Soul,” “Political Authority,” “Eclecticism,” “Dictionary,” and “Encyclopedia.”

The Encylopédie was read and discussed both abroad and in Paris, where, in the words of Harold Nicolson, “in the drawing rooms of Madame de Lambert, Madame de Tencin, Madame du Deffand, Madame Geoffrin, and Mademoiselle de l’Epinasse the intellectuals discussed little else.” More than a source of information, the work was a sub rosa political document, and as such a significant agent of change. The purpose behind it, Diderot wrote, was “changer la façon commune de penser,” or to change the manner in which people thought. In his article “Encyclopedia,” Diderot wrote that “this is a work that cannot be completed except by a society of men of letters and skilled workmen, each working separately on his own part, but all bound together solely by their zeal for the best interests of the human race and a feeling of mutual good will.”

The Encylopédie’s true intention was to secularize thought during a time when the Church and monarchy were supreme in France and in much of Europe. What Diderot and his confreres thought “the best interests of the human race” were not shared by the Church, monarchy, and much of the aristocracy. To make their views prevail the establishment had the weapon of censorship on its side. Censorship in that day had real muscle behind it; prison, even execution, could accompany it. Before he took up editorship of the Encylopédie, Diderot served three months in prison for an early essay called “Letter on the Blind for the Use of Those Who Can See,” and never afterward wrote without looking over his shoulder.

The Ultimate Freelance

Born in 1713 in the town of Langres, Champagne, Denis Diderot was the son of a cutler who specialized in knives and surgical instruments. His father was set on Denis one day joining the priesthood, and at ten years old he was sent off to a Jesuit college. At 12 he went through the ceremony of tonsuring (the practice of shaving part of one’s head, popularly associated with medieval monks). But the anti-authority impulse in the youthful Diderot was too strong for him ever to become a priest, and, though he completed the education required for the priesthood, he dropped away before taking final vows. He next took up the study of law, but with similarly incomplete results. When asked what he wanted to do with his life, Diderot is supposed to have replied, “Nothing, nothing at all. I like to study; I am very happy, very content. I don’t ask for anything else.” He was, as the future would bear out, the ultimate freelance.

As a freelance, the young Diderot scrabbled out a living. He did translations from Greek and English (among them Lord Shaftesbury’s An Inquiry Concerning Virtue, or Merit), a bit of writing of his own (his essay on blindness; his book, contra Pascal, Philosophical Thoughts), tutored the children of the rich, and read widely in literature, philosophy, and science. Isaac Newton, with whom it is sometimes said the European Enlightenment began, was, with his emphasis on experimentation, a potent influence on him.

Diderot claimed that the two great mistakes of his life were his marriage and the 25 years he gave to steering the Encylopédie to completion. His marriage at the age of 30 to Anne-Antoinette Champion was opposed by both their parents, and eventually, alas too late, came to be opposed by each of them. A harridan, relentless in her complaints, jealous, with a violent temper, she was, to put it gently, no comfort at all. They had four children, three of whom died; the one surviving child, their daughter Angélique, Diderot loved dearly.

Mistresses in 18th-century France were nearly as common as cellphones today. Everybody seemed to have one, and Diderot had several. Some of his love affairs lasted longer than others. One of his mistresses, a 38-year-old spinster named Sophie Volland, is said to have been the love of his life. Not notably attractive physically, she had a lively and penetrating mind. In his recent biography, Diderot and the Art of Thinking Freely, Andrew S. Curran writes that Diderot “cherished the fact that he could treat her as he might another (male) philosophe: she was honest and brainy, and blessed with, as one of Diderot’s Encylopédie colleagues put it, the ‘quick wit of a demon.’” So much did Sophie Volland meet the desideratum of a male mind in a woman’s body that she was known, as Curran reports, as the “hermaphrodite.” The relationship, he adds, was stronger on the spiritual than on the physical side. Diderot was haunted by the possibility that the woman he loved more than any other might have been in a lesbian relationship with her younger sister. He would go on to other love affairs, his relationship with Sophie Volland cooling and settling into the platonic. But their love for each other never died out. In her will she left him her eight-volume set of the Essays of Montaigne and a ring she loved.

In the early pages of his Catherine & Diderot Robert Zaretsky calls Diderot a “mensch,” a Yiddish word with richly complex meanings. A cognate with the German word for “human being” (Mensch), the Yiddish mensch is a clear approbative, describing a person of honor and integrity whose character has been developed through hardship. And so it seems with Denis Diderot, who most of his days feared censorship, underwent financial struggle until Catherine the Great bailed him out by buying his library and appointing him its salaried librarian, and returned at night to a complaining wife. Diderot was indeed a mensch, something one would never think to call Voltaire or Rousseau.

Diderot had his enemies—personal, institutional, ideological. He loathed superstition, a category under which he placed much of the religion of his time. “Religion,” he declared, “is a buttress which always ends up bringing the house down.” He went from seminarian, to deist, to atheist, though he was never a proselytizing atheist. (The word “agnostic,” it turns out, did not enter the language until 1869, when it was coined by T.H. Huxley.) Diderot was an early opponent of colonialism and of slavery in all its forms, from Russian to American. He thought liberty a gift bestowed upon all; unlike Voltaire who didn’t mind a benign monarch, Diderot was opposed to monarchy tout court, certainly all monarchy justified by the divine right to kingship. “No man has received from nature the right to command other men,” he wrote. “Freedom is a gift from the heavens, and each individual of the same species has the right to enjoy it as soon as he is able to reason.”

Uneven Fame

In his even-handed and well-written biography, Curran portrays a tireless Diderot, a battler under the flag of reason, carrying lifelong a torch for freedom. He accounts for Diderot’s uneven fame, even in our time, through his strangely erratic publishing history. Diderot wrote no one great book—no Social Contract, no Spirit of the Laws, no Candide—that might ensure his popular or permanent reputation. Much of what he did write, out of worry about the persecution that might come his way through censorship, was published posthumously. “Diderot’s unedited books, essays, and criticism,” Curran writes, “far surpassed what he had published during his lifetime.” Many of these, Curran adds, only “trickled out over the course of decades.” Rameau’s Nephew, doubtless his best-known work, made its first public appearance in German, translated by Goethe in 1805, well before it appeared in its original French, and even then the true manuscript in Diderot’s hand wasn’t recovered until 1891 and printed as he intended it until much later.

Many of these writings were censorable in Diderot’s day, and a few would get an R-rating in ours. All three of his novels are of interest, yet none is quite a success. The first, The Indiscreet Jewels, is a fantasy about a Congolese sultan who is given a magic ring that, when aimed at a woman, grants her vagina (her jewel) uninhibited speech. An amusing idea, but the problem is that it turns out the jewels haven’t all that much interesting to say. Some jewels decry being overused, some underused. Muzzles for jewels are soon invented to prevent their indiscretions. Diderot later inserted a few further chapters to give the novel philosophical weight: one in which the sultan’s consort dwells on the question of the residence of the soul in the body; another in which the ring is turned on the sultan’s favorite mare, which presents a problem in translation from animal to human language. Loftier critics than I see in Indiscreet Jewels a fable about hermeneutics, or interpretation, but as fiction the book doesn’t quite really come off.

Diderot’s next two novels, Jacques the Fatalist and His Master and The Nun could scarcely be more different from each other. The latter was written under the influence of Samuel Richardson’s Clarissa, the former under that of Laurence Sterne’s Tristram Shandy. Diderot’s fiction was more strongly influenced by English than French literature; and Goethe thought his true affinity was with German literature.

The Nun, written in the mode of naturalism, is about a young woman forced to live her life in a convent, presumably to expiate her mother’s sin of having had her out of wedlock, and is grimly anti-theological in its message. Jacques the Fatalist is, like Tristram Shandy, a satire on the very notion of storytelling. In both novels, characters’ stories are always being interrupted, and most never get finished, to remind the reader how arbitrary the telling of any tale is. Diderot pops in from time to time to remind his reader that he neglected to inform him of important details, or one character will ask another why he loathes character studies. At one point the reader (addressed as “You”) is told that he is “the one with the dirty mind”; at another the Master tells Jacques that “I doubt if there’s another head beneath the vast canopy of heaven that’s stuffed as full of paradoxical notions as yours.”

If Diderot’s fiction has a central flaw, it is that it is too obviously driven by ideas. In the best fiction, ideas arise naturally out of the moral conflict, out of the development of fictional characters and their tribulations and victories and defeats and what they learn from them. With Diderot’s fiction one has the sense that ideas, not story, are driving the bus.

Which is perhaps why those of Diderot’s compositions known as dialogues often show him at his best. In these dialogues—among them Rameau’s Nephew, Supplement to Bougainville’s Voyage, D’Alembert’s Dream, A Conversation between a Father and His Children—Diderot often plays the mischievous intellectual, questioning such fundamental beliefs as the necessary outlawing of incest, the importance of living up to the law, the superiority of the virtuous life. Supplement to Bougainville’s Voyage, Diderot’s addition to the travelogue of Louis-Antoine de Bougainville, who circumnavigated the globe from 1766-69, for example, is a conversation between a Tahitian wise man and the chaplain from Bougainville’s ship. When the chaplain tells the Tahitian, whom Diderot gives the name Orou, about the nature of the European God, Orou answers, “He sounds to me like a father that doesn’t care very much for his children.” In Rameau’s Nephew, the ne’er-do-well nephew of the famous musician, who openly avows a life given over to pleasure, says to his Diderot-like interlocutor in the dialogue, “Imagine the universe good and philosophical, and admit that it would be devilishly dull” and posits that the point of life is “to keep emptying one’s bowels easily, freely, pleasurably, copiously every night.” In A Conversation between a Father and His Children, the father reports discovering a long lost will that deprived poor relatives of an inheritance and does the conventionally correct thing by turning it in to the authorities, which gets from his son—called in the dialogue Diderot the Philosopher—the response that “[p]hilosophy is silent when the law is absurd.” At the dialogue’s close Diderot whispers in his father’s ear that “the truth is, there are no laws for the wise man.” This is the subversive Diderot, always interesting, never easily dismissed.

Counselor to Sovereigns

Did Diderot think himself primarily an artist, a philosopher, a social scientist avant la lettre? We cannot know. We do know that toward the end of his life he thought himself, in the tradition of Plato and Seneca, a counselor to sovereigns. (Recall that Plato’s mission to Syracuse to advise the tyrant Dionysius II ended in failure and Seneca’s to advise Nero ended in his own forced suicide.) Diderot’s mission to Catherine the Great, empress of all Russia—described with great economy and ironic penetration by Robert Zaretsky in Catherine & Diderot—is another record of the failure of philosophy to alter the path of power.

Catherine assumed the throne of Russia in 1762 after the suspicious death of her husband, Peter III. The initial reason given for the altogether inadequate Peter’s death was hemorrhoidal colic. We learn from Zaretzsky, though, that Peter was in fact assassinated by Alexei Orlov (the brother of one of Catherine’s lovers) and his fellow castle guards. Catherine was 33 at the time, well-read, thoughtful, and not in the least shy of power—ready to rule.

Francophile in her intellectual interests, German by birth, Catherine had earlier established connections with Voltaire and the sculptor Étienne-Maurice Falconet (who did the grand equestrian sculpture of Peter the Great that stands in Saint Petersburg); she was an admirer of the writing of Montesquieu. She knew Diderot through his art criticism and commissioned him to buy many of those paintings that would later become some of the central works of the Hermitage.

Diderot recommended Falconet to Catherine, and so when in 1776 she called on him to visit her in Saint Petersburg it was not altogether a surprise invitation. She had earlier bought his personal library, which she allowed him to keep in Paris until his death. Diderot viewed the invitation as an opportunity to put his own ideas into action through an already half-enlightened monarch. In his relation with Catherine, Zaretzsky writes, Diderot “sought the role not of Solon, but of Socrates.” He also assumed powers of persuasion and charm he ultimately did not possess.

The reviews on Diderot’s charm are mixed. The salonnière Madame Geoffrin, who eventually outlawed Diderot from her salon, reported to a friend that “[h]e is always like a man in a dream, and who believes everything he has dreamed.” The playwright and literary critic Jean-Françoise de La Harpe found Diderot altogether too delighted with his own conversation and, in Zaretzsky’s paraphrase, “his own most ardent and attentive listener.” This view seems to have been partially seconded by Diderot, who of himself said, “I’m high-minded and, on occasion, come across great and powerful ideas that I convey in a striking fashion.” Note the “on occasion.”

Once arrived in Saint Petersburg, Diderot met each afternoon from 3:00 to 5:00 with Catherine. She was initially much taken with him. “Diderot’s imagination, I find,” she told Voltaire, “is inexhaustible. I place him among the most extraordinary men who have ever lived.” He in turn described her as possessing “the soul of Caesar and all the charms of Cleopatra.” During their sessions together he in his intellectual passion often grabbed her arms, slapped her legs, and she soon complained that “I cannot get out of my conversations with him without having my thighs bruised black and blue. I have been obliged to put a table between him and me to keep myself and my limbs out of range of his gesticulation.” In his rambles, she reported, “at times he seems to be one hundred years old, but at others he doesn’t seem to be ten.”

About what did Diderot harangue the empress? About the evils of serfdom, the need to do away with censorship, the centrality of law, the baleful effects of religion, the importance of education, in short, the standard Enlightenment program. He felt his message was getting across. The empress, he noted “loves the truth with all her soul, and although I have at times told truths that rarely reach the ears of kings, she has never been wounded.” Fascinated by him Catherine may have been, but he sensed that, as Andrew Curran puts it, “she was not taking his ideas to heart.” When he queried her about not having put any of what he told her in effect, she replied: “In your plans for reform, you forget the difference between our two roles: you work only on paper which consents to anything: it is smooth and flexible and offers no obstacles either to your imagination or to your pen, whereas I, poor empress, work on human skin, which is far more prickly and sensitive.” After a five-month visit, which ended in March 1774, Diderot departed Russia, writing to his friend Madame Necker that “I would be an ingrate if I spoke ill of it, and I would be a liar if I spoke well of it.”

First Step

Diderot seems to have spent his final decade under the shadow of failing health. This, though, did not greatly reduce his high literary productivity. He wrote a 500-odd page study of Seneca; he is said to have contributed substantially to Guillaume Thomas Raynal’s History of the Two Indies. He held out hope that his ideas would find seed in America. He connected with Benjamin Franklin, though it is less than clear that the two men ever met. He allowed that he had failed to produce a single masterwork, yet, according to Curran, held out the hope that his ideas “would change society for the better.” Toward the end he summed up his final views: “There is only one virtue, justice; only one duty, to make oneself happy; only one corollary, not to exaggerate the importance of one’s life and not to fear death.” Earlier he had written: “I will be able to tell myself that I contributed as much as possible to the happiness of my fellow men, and prepared, perhaps from afar, the improvement of their lot. This sweet thought will for me take the place of glory. It will be the charm of my old age and the consolation of my final moment.”

Toward the very close of Catherine & Diderot Zaretzsky notes that Montesquieu portrayed society as it was, Diderot as it ought to be. Diderot, his mind always on the future, may be said to have lived in the ought. He died five years before the French Revolution, which subscribed to many of his central ideas, yet he could hardly have approved of the Terror. What would he have made of the fate of these same ideas in the centuries since his death, centuries that featured the demise of monarchy, the lessening of the power of religion, the rise of democracy, but also the eruption of world wars, the emergence of murderous totalitarianism, the invention of weapons of mass destruction? Would he have recognized that his beloved reason alone, as far as it goes, never goes far enough?

Diderot’s daughter remembers the last words she heard from her father: “The first step towards philosophy is incredulity.” Were Denis Diderot alive today to consider the world of our day, he might wish to add that the final step toward philosophy also happens to be incredulity.