French philosopher, and man of letters, the chief editor of the L'Encyclopédie, one of the principal literary monuments of the Age of Enlightenment. The work, created for " for the best interests of the human race and a feeling of mutual good will," took 26 years of Diderot's life. In seventeen volumes of text and eleven of illustrations, it presented the achievements of human learning in a single work. Besides offering a summary of information on all theoretical knowledge, it also challenged the authority of the Catholic Church. Ideas, that would never get past the censors, Diderot hid in the cross-references, which served as the basis for the contrary truths.

"The good of the people must be the great purpose of government. By the laws of nature and of reason, the governors are invested with power to that end. And the greatest good of the people is liberty. It is to the state what health is to the individual." (L'Encyclopédie, from an article on Government, in The Confessions of a Moral Atheist by Brett Stillman, 2006, p. 140)

Denis Diderot was born at Langres, the son of a successful cutler. He was first educated by the Jesuits (1728-32). During this period he devoured books of all kinds – his favorites were such classics as Horace and Homer. In 1732 Diderot received the master of arts degree from the University of Paris. His father expected him to study medicine or law, but Diderot spent his time with books and women. When his financial support was ended, Diderot then worked for the attorney Clément de Ris (1732-34), and as a tutor, freelance writer, and bookseller's hack (1733-44).

After ten bohemian years, Diderot married in 1743 Anne Toinette Champion. To support his own family, he began to translate texts from English to France. As the years went by, however, their marriage turned sour. When his wife said she would not touch a book which did not offer something spiritually uplifting, Diderot's remedy was to read her only raunchy works. "What amuses me is," Diderot confessed in a letter, "that she treats everyone who visits her to a repeat of what I have just read her, so conversation doubles the effect of the remedy.  I have always spoken of novels as frivolous productions, but I have finally discovered that they are good for the vapours." (A History of Reading by Alberto Manguel, 1997, p. 121) Diderot found also a new love, Madeleine de Puisieux. She was a writer, whose best work, Les caractères (1750-51), appeared during their affair. With Sophie Volland Diderot had a liaison from about 1755 until her death in 1784. Diderot's letters to her belong to the important sources of his personal life and reveal ways of thinking in that era.

Diderot gained first notice in the 1740s as a translator of English books. However, in the beginning Diderot's knowledge of the language was not the best possible. He used an English-Latin dictionary, and translated Latin words into French. Temple Stanyan's Grecian History came out in 1743. It was followed with Lord Shaftesbury's Inquiry Concerning Virtua and Merit (1745), and Robert James' Medicinal Dictionary (1746-1748). The money Diderot earned from the translation of Shaftesbury's book he gave to de Puisieux. For her he also wrote Les bijoux indiscrets (1748), an erotic novel. It was printed in Holland. In his later years Diderot regretted having written it.

"When asked one day whether there were any true atheists on Earth, a man responded: "Do you believe that there any true Christians?"" (Philosophical Thoughts and Other Texts, translated by Kirk Watson, 2019, p. xix)

The anonymously published Pensées philosophiques (1746), a collection of aphorisms, was burned by the Parliament of Paris for its anti-Christian ideas. La Promenade du sceptique, completed in 1747, was not published until 1830. Lettre sur les aveugles (Letter on the Blind) opened up the question of the existence of God, and Diderot was imprisoned in 1749 for three months for his opinions. When Bastille was full in July 1749, the writer was taken to prison at Vincennes. In Essai sur le Mérite de la Vertu (1745) he had stated: "From fanaticism to barbarism is only one step." (Bartlett's Familiar Quotations by John Bartlett, Eighteenth Edition, 2012, p. 313)

In 1745 Diderot became the editor of the Encyclopédie with mathematician Jean Le Rond d'Alembert, who resigned later because he believed that mathematics was a more fundamental science than biology. Diderot himself was fascinated by discoveries in the biological sciences. Originally the work was planned to be a translation of Ephraim Chambers's, a Scottish globemaker, two-volume Cyclopaedia. Diderot enlarged its scope and made it an organ for radical and revolutionary opinions, which he managed to slip into seemingly minor articles. In his article on Macchiavellianism Diderot attributed to this Florentine thinker the technique of undermining a political institution by pretending to defend it:  "When Machiavelli wrote his treatise on The Prince, it is as if he said to his fellow citizens: read this work carefully. Should you ever accept a master, he will be such as I depict him to you. Here is the savage brute to whom you will be abandoning yourselves. Thus it was the fault of his contemporaries if they misjudged him: they took a satire for a eulogy". (Machiavelli and Us by Louis Althusser, edited by François Matheron, 1999, p. 31)

Whilst remaining fully aware of the enormous cultural and political weight of the project, Diderot occasionally expressed his doubts about its usefulness, as he did in the famous article about Aguaxima: "AGUAXIMA (Hist.nat.bot.), a plant growing in Brazil and the islands of middle America. This is all we are told; & I would like to ask for whom descriptions like this are made at all. It cannot be for the natives of country, who obviously know more characteristis of the aguaxima than this description contains & who have no need of being informed that it grows in their own country. . . . It is also not made for us; for what does it matter if there is in Brazil a tree that is called aguaxima of which we know nothing but the name? To whom is this name useful?" (A Wicked Company: The Forgotten Radicalism of the European Enlightenment by Philipp Blom, 2010, p. 247) Diderot signed 1,984 articles of the first volume; in the last three volumes, his original contributions had dwindled to 7, 8, and 6 respectively, indicating his disillusionment.

The Encyclopédie was published between 1751 and 1772 in 17 volumes of text and 11 volumes of engravings. Many of the contributors were priests, but Diderot's companions in the enterprise were also Voltaire, Chevalier de Jaucourt, a tireless reseacher, and Marmontel. The Encyclopédie arose much controversy and the publisher was jailed, then released, and his licence canceled. Fortunately, the censor, M. de Malesherbes, was a believer in freedom of the press, and warned beforehand Diderot when his agents were sent to seize manuscripts.

While editing the Encyclopédie (1745-1772), Diderot composed most of his own important works as well, among them Lettre sur les sourds et muets (1751), Pensées sur l'interprétation de la nature (1753), the novel La religieuse (1760), and the dialogue Le neveu de Rameau (1761), which he revised several times. It was not included in Diderot's Œuvres, published in 1798; his fellow countrymen had been indifferent to it. Diderot gave one copy to Goethe, who translated it into German. Diderot's moral plays Le fils naturel (1757) and Le père de famille (1758) gained a mediocre success. He had called for a new kind of expression on the stage, more natural portrayal of life. From 1759 he contributed notes on the biennial Salon to the collections of his friend, Friedrich Grimm. He appreciated spontaneity, criticized the tyranny of rules, but in his 'Essay on Painting' he also stated, "there is one thing that painting and poetry have in common: they should both be moral." (Modern Theories of Art, 1: From Winckelmann to Baudelaire by Moshe Barasch, 1990, p. 131)

La religieuse was "une pure infamie" and scarcely known before its publication in 1796, during the French Revolution. In the story a young girl, Suzanne, enters a nunnery and is harassed by a lesbian abbess, Sister Sainte-Christine. Eventually her nature is corrupted and she develops lesbian attachment to Mme de Chelles. Diderot used the technique of first-person narration: "The Superior came into my cell. She was accompanied by three Sisters. One brought a stoup of holy water, the second a crucifix, the the third some ropes. The Superior said to me in a loud and threatening voice: 'Get up... kneel down and commend your soul to God!'" (Memoirs of a Nun, translated by Francis Birrell, 1992, p. 88) Diderot and his friend Grimm created the story in order to lure their acquaintance, the Marquis de Croismare, to return to Paris. The marquis had shown interest in the case of a nun, who had failed to break her vows. Diderot sent letters in her name to the marquis, as if she had escaped her convent and was looking for his help. From these letters he composed the book. In the 1960s Jacques Rivette and Jean Grualt made a play from the book and also adapted it into a film, which was banned in France.

Because of his radical thoughts several of Diderot's books were confiscated and came out posthumously. Supplement au Voyage de Bougainville, in which he indicted slavery and colonialism, was not published until 1796. An old Tahitian man tells the protagonist, who is leaving the island: "We are a free people; and now you have planted in our country the title deeds of our future slavery. You are neither god nor demon; who are you, then, to make slaves? Orou! You understand the language of these men, tell us all, as you have told me, what they have written on this sheet of metal: 'This country is ours.' This country yours? And why? Because you have walked thereon? If a Tahitian landed one day on your shores, and scratched on one of your rocks or on the bark of your trees: 'This country belongs to the people of Tahiti' – what would you think?" ('Denis Diderot The Fall of  Natural Man,'  The Anarchists, edited by Irving Louis Horowitz,  2005, p. 67)

In 1765 Diderot sold his library to Catherine II of Russia to increase her daughter's dowry. The Empress gave him money to improve the collections and for other similar services. During 1773 and 1774 Diderot made a long and difficult journey to St. Petersburg to thank Catherine personally and plan the creation of a Russian university. "Diderot's imagination, I find, is inexhaustible," Catherine told Voltaire. "I place him among the most extraordinary men who have ever lived." (Catherine & Diderot: The Empress, the Philosopher, and the Fate of the Enlightenment by Robert Zaretsky, 2019, p. 150) According to a famous anecdote, the Empress staged a debate between the Swiss mathematician Leonard Euler and Diderot. The pious Euler threw down the challenge to the atheist Diderot, "Monsieur, (a+bⁿ)/n=x, therefore God exists. Reply!" Diderot did not know what to say and Euler won the debate. Actually he was a very good mathematician and would have been unlikely to fall for a meaningless proof.  (The God Delusion by Richard Dawkins, 2007, p. 109)

The hardships of the journey weakened Diderot's health, which was never robust. The visit ended in March 1774. Before leaving for Russia he started to write Jacques le fataliste et son maître (1771-73).

Diderot's humorous, freewheeling story of Fate and individual choice, showed the influence of Cervantes, Laurence Sterne's Tristram Shandy, and Voltaire's Candide. The central charaters are a servant, Jacques, and his master, a knight whose name is never told. Jacques tells his master that his Captain used to say that everything good or bad that happens us here below is written on high. He asks, is there any way of rubbing out what is written up there? The Italian writer Italo Calvino has called Jacques an anti-Candide, "because it was conceived as an anti-conte-philosophique: Diderot is convinced that truth cannot be constrained into one form, or into one didactic fable." (Why Read the Classics? by Italo Calvino, translated from the Italian by Martin McLaughlin, 2000, p. 111) The tale of Madame de la Pommeraye, which Jacques and his Master hear at an inn, was translated into German by Friedrich Schiller (1785).

Among Diderot's friends were such philosophers and literary figures as Rousseau, with whom the friendship ended in 1757, Hume, Helvétius, Abbé Raynal, Lawrence Sterne, Marmontel, and Sedaine. When the Encyclopédie started to appear, Roussau was enthusiastic for the views it expressed, and founded a journal to promote the work. Later he established with his brother-in-law a new printing house, issuing novels and stories of Voltaire, the Fables and Contes of La Fontaine, a complete set of Diderot's works, and other works by writers and propagandists for the Enlightenment. Diderot died of emphysema and dropsy in Paris on July 31, 1784. According to a story, his wife tried to prevent him from eating an apricot that he had in his hand. "But what the devil do you think that will do to me?" he said, ate it anyway and died suddenly. (Last and Near-Last Words of the Famous, Infamous and Those In-Between by Joseph W. Lewis, Jr., M.D., 2016, p. 187)

Diderot was a pivotal figure of the entire century, but his later reputation was shadowed by the brilliance of his two contemporaries, Voltaire and Rousseau. Both Marx and Engels held him in high esteem and Marx referred to Diderot as his favorite prose writer. The Bolshevik leader V.I. Lenin even attempted to make him a precursor of dialectical materialism in his philosophical work Materialism and Empirio-criticism (1909).

For further reading: Censoring of Diderot's "Encyclopédie" and the Re-established Text by Douglas H. Gordon and Norman L. Torrey (1947); Diderot: The Testing Years 1713-1759 by Arthur M. Wilson (1957); Diderot et l'Encyclopédie by Jacques Proust (1962); Diderot: The Embattled Philosopher by Lester G. Crocker (1966); The Philosophy of the Enlightenment by Ernst Cassirer (1968); Diderot by Otis Fellows (1977); Diderot, critique d'art by Else Marie Bukdahl (1980); Diderot by Peter France (1983); Diderot: Tresholds of Representation by James Creech (1986): Diderot and a Poetics of Science, ed. by Suzanne Pucci (1986); Socratic Satire: An Essay on Diderot and Le Neveu De Rameau by Stephen Werner (1987); Bibliographie de Diderot by Frederick A. Spear (1980-88); Diderot: A Critical Biography by P.N. Furbank (1992); A Social History of Knowledge: From Gutenberg to Diderot by Peter Burke (2000); Enlightening the World: Encyclopédie, the Book That Changed the Course of History by Philipp Blom (2005); A Wicked Company: The Forgotten Radicalism of the European Enlightenment by Philipp Blom (2010); Diderot and Rousseau: Networks of Enlightenment by Marian Hobson (2011); Narrative Structure and Philosophical Debates in Tristram Shandy and Jacques le fataliste by Margaux Elizabeth Whiskin (2014); Catherine & Diderot: The Empress, the Philosopher, and the Fate of the Enlightenment by Robert Zaretsky  (2019); Denis Diderot's Enlightenment by Joseph Epstein (2019); Diderot and the Art of Thinking Freely by Andrew S. Curran (2020); Prose of the World: Denis Diderot and the Periphery of Enlightenment by Hans Ulrich Gumbrecht (2021) - See also: Voltaire (1694-1778) who also spoke against established religious and political systems. Mme de Staël met Diderot in her childhood in her mother's salon.

Selected publications:

• Histoire de Grèce, by Temple Stanyan, 1743 (3 vols.; translator)
• Principles de la philosophie morale / Shaftesbury, 1745 (rev. ed. as Philosophie morale réduite à ses principles, 1751; translator)
• Essai sur le mérite et la vertu, 1745
• Pensées philosophiques, 1746
  - Philosophical Thoughts (translated by Margaret Jourdain, in Diderot's Early Philosophical Works, 1916) / Philosophical Thoughts and Other Texts (translated by Kirk Watson, 2019)
• Dictionnaire universel de médecine, by Robert James, 1746-48 (6 vols.; translator, with Marc-Antoine Eidous and François-Vincent Toussaint)
• La Promenade du sceptique, 1747 (published in 1830)
  - Skeptic's Walk (translated by Kirk Watson, 2018)
  
• Mémoires sur différens suject de mathématiques, 1748
• Les bijoux indiscrets, 1748
  - The Indiscreet Toys (tr. 1749)
• Lettre sur les aveugles, 1749
  - An Essay on Blindness (tr. 1750) / Letter on the Blind (translated by Margaret Jourdain, in Diderot's Early Philosophical Works, 1916)
• Lettre sur les sourds et muets, 1751
  - Letter on the Deaf and Dumb (translated by Margaret Jourdain, in Diderot's Early Philosophical Works, 1916)
• Encyclopédie; ou, Dictionnaire raisonné des sciences, des arts, et des métiers, par une sociéte de gens de lettres, 1751-1765 (17 vols., ed. with Jean de Rond d'Alembert; Recuil de plances, 11 vols., 1762-72)
  - A Diderot Pictorial Encyclopedia of Trades and Industry: Manufacturing and the Technical Arts in Plates Selected from L'Encyclopédie (edited by Charles C. Gillispie, 1959) / Encyclopedia: Selections (translated by Nelly S. Hoyt and Thomas Cassirer, 1965) / Denis Diderot’s The Encyclopedia: Selections (edited and translated by Stephen J. Gendzier, 1967) / Diderot Encyclopedia: The Complete Illustrations, 1762-1777 (5 vols., 1978) 
• Pensées sur l'interprétation de la nature, 1753
• Le Fils naturel; ou, Les Épreuves de la vertu, 1757 (play, prod.)
  - Dorval; or, The Test of Virtue (tr. 1767) / Two Plays by Denis Diderot: The Illegitimate Son and The Father of the Family (translated with an introduction by Kiki Gounaridou, John Hellweg, 2011)
  
• Discours sur la poésie dramatique, 1758
• Le père de famille, 1759 (play, prod.)
  - The Father (tr. 1770) / The Family Picture (tr. 1781) / Two Plays by Denis Diderot: The Illegitimate Son and The Father of the Family (translated with an introduction by Kiki Gounaridou, John Hellweg, 2011)
  
• Le Neveu de Rameau, 1760-62
  - Rameau's Nephew (translated by Leonard Tancock, 1976; Margaret Mauldon, 2006) / Rameau’s Nephew, and Other Works (translated by Jacques Barzun and Ralph H. Bowen, 1956)
  - Rameaun veljenpoika (suom. Edwin Hagfors, 1921; Kauko Kare, 1970)
• Eloge de Richardson, 1761
• Réflections sur Térence, 1762
• Le rêve de d'Alembert, 1769
  - D'Alembert's Dream (translated by Leonard Tancock, 1976)
• Les Oeuvres de Shaftesbury, 1769 (3 vols.; translator)
• Leçons de clavecin et principles d'haromonie, 1771
  - Music Made Easy to Every Capacity, in a Series of Dialogues (translated by Giffard Bernard, 1778)
• Oeuvres philosophiques, 1772 (6 vols.)
• Les deux amis de Bourbonne, 1773
• Contes moraux et nouvelles idylles, 1773 (with Salomon Gessner, edited by J.-H. Meister)
• Le paradoxe sur le comédien, 1773 (published 1830)
  - The Paradox of Acting (translated by Walter Herries Pollock, 1883) / Masks or Faces?: A Study in the Psychology of Acting (translated by William Archer, 1888) / The Paradox of the Actor (translated by Geoffrey Bremner, in Denis Diderot, Selected Writings on Art and Literature, 1994)
  - Näyttelijän paradoksi (suom. Marjatta Ecaré & Aale Tynni, 1987)
• Éléments de physiologie, 1774-84
• Observations sur le Nakaz, 1774
  - Observations on the Nakaz (edited and translated by John Hope Mason, Robert Wokler, in Diderot: Political Writings, 1992)
• Essai sur Sénèque, 1778 (rev. ed., Essai sur les règnes de Claude et de Néron, 1782)
• Essai sur les règnes de Claude at de Néron, 1782
• Est-il bon? Est-il méchant, 1784 (play, prod. 1913)
  - Denis Diderot, Wicked Philanthropy: A Translation of Est-il bon? Est-il méchant? (translated by Gabriel John Brogyanyi, 1986)
• Essai sur la peinture, 1795 (written 1765)
• Supplément au voyage de Bouganville, 1796
  - Supplement to Bougainville's Voyage (edited and translated by John Hope Mason, Robert Wokler, in Diderot: Political Writings, 1992)
• Jacques le fataliste et son maître, 1796 (written 1771-73)
  - James the Fatalist and His Master (tr. 1797) / Jacques the Fatalist and His Master (translated by J. Robert Loy, 1959; Michael Henry, 1986; David Coward, 1999) / Jack the Fatalist and His Master (translated by Wesley D. Camp and Agnes G. Raymond, 1984)
  - Jaakko Fatalisti ja hänen isäntänsä (suomentanut Jukka Mannerkorpi, 1992)
  - Films: Les Dames du Bois de Boulogne (1945), dir. by Robert Bresson, starring Maria Cesares and Elina Labourdette, screenplay by Robert Bresson and Jean Cocteau; O Fatalista (2005), dir. by João Botelho, starring Rogério Samora, André Gomes, Rita Blanco
  
• La Religieuse, 1796 (written 1760)
  - The Nun (tr. 1797) / Memoirs of a Nun (translated by Francis Birrell, 1959) / The Nun (translated by Eileen B. Hennessy, 1968; Leonard Tancock, 1972; Russell Goulbourne, 2005)
  - Films: La Religieuse (1966; forbidden in France), dir. by Jacques Rivette, starring Anna Karina, Micheline Presle, Liselotte Pulver, Francine Bergé, screenplay by Jean Grualt and Jacques Rivette. "Both book and film seek to expose eighteenth-century convent life in France and, by doing so, explore the subject of human freedom – convent life for Diderot and Rivette is seen as a denial of human nature and the source of repression and suffering." (Ira Koningsberg in Modern European Filmmakers and the Art of Adaptation, edited by Andrew S. Horton and Joan Magretta, 1981); La Religieuse (2013), dir. by Guillaume Nicloux, starring Pauline Etienne, Isabelle Huppert, Louise Bourgoin
  
• Le Joueur, 1819 (play, based on The Gamester by Edward Moore)
• Mémoires, correspondances, et ouvrages inédits, 1830-31 (4 vols.)
• Œuvres complètes, 1875-77 (20 vols., edited by Jean Assezat and Maurice Tourneaux)
• Correspondance littéraire, philosophique et critique, 1877-82 (edited by Maurice Tourneaux)
• Mémoires pour Catherine II, 1899
• Diderot's Early Philosophical Works, 1916 (translated by Margaret Jourdain)
• Observations sur la Nakaz, 1920
• Dialogues, 1927 (translated with an introd. by Francis Birrell)
• Lettres à S. Voland, 1930
  - Diderot’s Letters to Sophie Volland (translated by Peter France, 1972)
• Diderot, Interpreter of Nature: Selected Writings, 1937 (translated by Jean Stewart and Jonathan Kemp)
• Lettres à Sophie Volland, 1938 (edited by André Babelon)
  - Diderot's Letters to Sophie Volland (a selection translated by Peter France, 1972)
• Selected Philosophical Writings, 1953 (edited by J. Lough)
• Correspondande, 1955-70 (edited by Georges Roth) Vernière)
• Les Salons, 1957-67 (4 vols., edited by Jean Séznec and Jean Adhémar)
• Oeuvres esthétiques, 1959 (edited by Paul Vernière) 
• La Rêve de d'Alembert, 1962 (edited by Jean Varloot)
• Oeuvres politiques, 1963 (edited by Paul Vernière)
• Œuvres romanesques, 1962 (edited by Henri Bénac)
• Rameau's Nephew and Other Works, 1964 (edited by R.H. Bowen)
• Éléments de physiologie, 1964 (edited by Jean Mayer)
• Les œuvres romanesques, 1964
• Encyclopdia: Selections, 1965 (edited by Nelly S. Hoyt and Thomas Cassirer)
• Selected Writings, 1966 (edited by Lester G. Crocker, translated by Derek Coltman)
• Essai sur les règnes de Claude at de Néron, 1966 (2 vols.)
• Œuvres complètes, 1969-77 (15 vols., edited by Roger Lewinter)
• Œuvres complètes, 1975-<c2004> (v. <1-11, 13-20, 23-25>; edited by H. Dieckmann, Jean Varloot, and Jacques Proust)
• The Irresistible Diderot, 1982 (edited by John Hope Mason)
• Political Writings, 1992 (translated and edited by John Hope Mason and Robert Wokler)
• This Is Not a Story and Other Stories, 1993 (translated by P.N. Furbank)
• Œuvres, 1994-1997 (5 vols., edited by Laurent Versini)
  
• Selected Writings on Art and Literature, 2004 (translated with an introduction and notes by Geoffrey Bremner)
• Diderot on Art, 1995 (2 vols.; edited and translated by John Goodman; introduction by Thomas Crow)
• Thoughts on the Interpretation of Nature, and Other Philosophical Works, 1999 (introduced and annotated by David Adams)
• Contes et romans, 2004 (edited by Michel Delon, et al.) 
• Oeuvres philosophiques, 2010 (edited by Michel Delon and Barbara de Negroni)
  
• Philosophical Thoughts and Other Texts, 2019 (translated by Kirk Watson)