Diderot, DENIS, was born on October 15, 1713, at Langres, in Champagne, where his family had for two centuries been engaged in the manufacture of cutlery. An eldest son, he was intended for the church, and received his early training at the Jesuit school in his birthplace. After studying at the Collège d'Harcourt in Paris, he offended his father by refusing to become either a lawyer or a physician, and was in consequence flung upon his own resources. From 1734 until about 1744 he led a life of haphazard, ill-paid toil as a tutor and a bookseller's hack. In 1743 he married Annette Champion, a young sempstress, against the wishes of her friends, and without the knowledge of his family. After she had borne him a son, he persuaded his wife to remove with the child to Langres, where she brought about a reconciliation between Diderot and his father. His marriage, however, did not prove a happy one. During his wife's absence in Champagne he formed a liaison with a Madame Puisieux which lasted for several years; and later in life he became attached to a financier's daughter, Mademoiselle Voland, to whom he remained devoted until her death in 1774. His Pensées Philosophiques were burned by order of the Parliament of Paris in 1746, and three years afterwards he underwent imprisonment for the opinions expressed in his Lettre sur les Aveugles. His appointment to the editorship of an encyclopædia which the bookseller, Le Breton, had resolved upon publishing, assured him of a regular income, and gave him a commanding position in the world of letters. Le Breton's intention had been merely to issue an expanded version of the English Cyclopædia of Ephraim Chambers, which had appeared in 1727. But in Diderot's hands the character of the work was transformed. He enlisted nearly all the important French writers of the time as contributors, and in place of a storehouse of useful information, produced an engine of war for the philosophe party (see ENCYCLOPÆDIA). For some twenty years he stood at his post in spite of dangers and drawbacks, before which even a strong man might pardonably have flinched. The book was again and again threatened with prosecution; its sale was more than once prohibited; its editor ran a constant risk of imprisonment or exile. D'Alembert, at one time co-editor with Diderot, forsook him in despair at the obstacles to be overcome. But his marvellous energy, his varied knowledge, above all, his faculty of rallying and inspiring his fellow-workers, enabled Diderot to carry his vast undertaking to a successful conclusion. The first volume appeared in 1751; the last, in 1765. In his later years Diderot fell into pecuniary difficulties from which he was rescued by Catharine II. of Russia, who purchased his library, but allowed it to remain in Paris, and installed him at a salary as its caretaker. In 1773 he paid a visit to his benefactress, by whom he was most cordially received. He returned to Paris after spending five months in the palace of the empress at St Petersburg, and four months at the Hague as the guest of Prince Galitzin. During his old age he lived principally in his study at the corner of the Rue Taranne, spending his days in reading and meditation, in directing the studies of his daughter—the only survivor of his four children, in the giving of good counsel, and the doing of good works. He died from a stroke of apoplexy on the 30th July 1784.
One of the most prolific and versatile, Diderot was also one of the most careless of writers. He worked in almost every department of literature. He was a novelist and a dramatist, a satirist, a philosopher, a critic of pictures and books; while as a letter-writer he was surpassed by none of his contemporaries. His published works are far from embodying the results of his labours as an author. He was ever ready to contribute without reward, often without acknowledgment, to the writings of others; he has been well termed the munificent prodigal of letters. His efforts in fiction include a story in the manner of Crébillon, described by Carlyle as 'the beastliest of all past, present, or future dull novels'; La Religieuse, a powerful story written with the object of exposing the evils of conventual life; and Jacques le Fataliste, a collection of short tales of which some are good and others indifferent, while one of them is a little masterpiece. Le Neveu de Rameau, an imaginary conversation between the author and a parasite of the great, is probably the strongest as it is the most curious of all Diderot's works. In the course of this dialogue, which was translated by Goethe, the follies and corruptions of society are laid bare with sardonic humour and piercing insight. Diderot's plays were somewhat unsuccessful examples of what was then known as tragédie bourgeoise, or of what we should now term melodrama. His happiest dramatic efforts were two short pieces which were never acted, La Pièce et la Prologue and Est-il Bon? Est-il Méchant? The letters which he addressed to Mademoiselle Voland, and which were first published some fifty years after his death, form the most interesting section of his voluminous correspondence. They give an entertaining and wonderfully vivid picture of the life that was led in the Baron d'Holbach's country-house at Grandval, the headquarters of the most advanced members of the philosophie party. As a critic Diderot stood far in advance of his contemporaries, and anticipated the Romanticists in advocating a return to nature and in seeking to free the drama from the trammels which had been imposed on it by the classical school. His criticisms bear the marks of over-hasty production, but their originality, shrewdness, and abounding vivacity more than atone for the lack of literary finish. His Salons, remarks on pictures exhibited at different times in Paris, are the earliest example of aesthetic criticism in modern literature. His philosophical works include Pensées Philosophiques, La Promenade du Sceptique, Lettres sur les Sourds et Muets, Lettre sur les Aveugles, La Rêve d'Alembert, Essai sur la Vie de Sénèque, L'Interprétation de la Nature, and a long criticism on Helvétius's treatise De l'Homme. Diderot has been frequently described as an atheist; whether justly or not is a matter very hard to decide. He was at one time deeply influenced by the naturalistic religion of Shaftesbury, and that writer's influence upon his mind was never wholly effaced. In certain passages he appears to write as a pantheist. But he never set forth his philosophy in consistent and systematic form.
Diderot is so unequal a writer that his works must be read in the mass before a just estimate can be formed of his extraordinary gifts. His keenest sayings, his most pregnant thoughts, are frequently imbedded in dullness. An indefatigable worker, he yet never took his work seriously enough. He lacked the faculty of concentration and the artist's mastering sense of form. His prose is not sustained at a high level of excellence; he sins grievously against good taste; his thoughts are not seldom crude and shallow; his mannerisms—notably his abuse of apostrophe—his 'sensibility' and his philosophie cant are not a little trying to the reader. But with all their defects his writings are wonderfully alive—fertile in original ideas—racy with a stimu- lating flavour which is all their own; abounding in careless felicities of phrase and in sayings which flash a new light into human nature; rich with the sap of a humour which resembles the humour of no other Frenchman, and which Carlyle has likened to the humour of Cervantes. Inferior to Voltaire and Rousseau as a literary craftsman, he was a deeper thinker than either; his knowledge of men was profound, and his learning was truly encyclopaedic. Ardent and generous, though lacking in self-restraint, he was one of the best of friends and the most charming of companions. In the opinion of his contemporaries his powers as a conversationalist eclipsed his gifts as a writer. He appears to have possessed an unrivalled faculty of improvisation; to judge from the testimony of shrewd critics who list next to him, his talk was as pointed and pregnant in its substance as captivating in its eloquence. 'He who knows Diderot only in his writings,' said Marmontel, 'does not know him at all.'
The most complete edition of his works is that by Assézat and Tourneur (20 vols. 1875-77). See the study by Rosenkranz (Leip. 1866); John Morley's Diderot and the Encyclopaedists (2 vols. 1878); E. Scherer's study (1880); Sainte-Beuve's Portraits Littéraires, Carlyle's Miscellanies; and French monographs by Reinach (1894), Collignon (1895), Ducros (1895), and Tourneux (1899).