Because of his public leadership of thephilosophe party ineighteenth-century France, Voltaire stands today as the iconic exampleof the French Enlightenment philosopher. Denis Diderot(1713–1784) is often seen as Voltaire’s second in thatrole since it was around both men that the Enlightenmentphilosophes rallied as a movement after 1750. The epochalproject, which Diderot jointly pursued with Jean le RondD’Alembert, to “change the common way of thinking”through a comprehensiveEncyclopedia, or Reasoned Dictionary ofthe Arts, Sciences, and Trades provided the emergentphilosophe movement with the cause around which they wouldcoalesce. Diderot also fought vigorously with Voltaire on behalf oftheEncyclopédie project and its principles, becomingas a result a public leader of the Enlightenment philosophical partyin France alongside Voltaire. He also worked, like Voltaire, as awriter and critical intellectual who willingly positioned himselfagainst the grain of established authority, and one who usedphilosophy as a vehicle for political and social activism. YetDiderot’s philosophy pursued many more agendas and dimensionsthan Voltaire’s. He also left behind a corpus of philosophicalwritings that marks him out as arguably the most sophisticated of allthe Enlightenmentphilosophes, and as one of the greatphilosophical thinkers of the eighteenth-century.

Despite the obvious sophistication of Diderot’s philosophy, hislegacy has suffered because of the historical differences separatinghis writings from the discipline of philosophy as it is practicedtoday. Enlightenmentphilosophie was something very differentfrom what professional academic philosophers mean by that term today,and Diderot’s writings are often ignored by modern philosophersbecause they do not appear to be philosophy as they know it. Like manyEnlightenmentphilosophes, Diderot also worked as anhomme de lettres first and foremost, and only as aphilosopher narrowly construed in certain instances. He also neverauthored any recognizable work of “systematic philosophy”if by that term we mean writing in the vein of his contemporaries suchas David Hume in hisTreatise or Immanuel Kant in hisCritiques.

Yet Diderot made important contributions to modern philosophy, and ifthey are to be grasped, the historical differences separating hiswriting from philosophy today must be transcended, and his eclecticmanner of working accepted and embraced. Diderot wrote works that werecognize today as philosophy, but he also wrote a great deal morethan that, and the challenge presented by his eighteenth-centuryphilosophie is to see the modern philosophy contained in allof it. For Diderot did not simply write plays, art criticism, prosefictions, and highly imaginative works of literature alongside hiswork in philosophy; he pursuedphilosophie through theseostensibly literary works as well. He experimented with genres,including philosophical genres, when crafting his thought, and hiswriting overall is redolent with a self-consciousness that makes anyeasy separation of his explicitly philosophical writings from hisliterary work well-nigh impossible. His publishing habits weresimilarly complex, for as a writer who suffered personally undercensorship that made the traffic in illicit ideas a prosecutableoffense in Old Regime France, Diderot often had very good reason toleave his work unpublished—and very often did. At the same time,censorship alone does not explain the peculiar mix of published andunpublished writings found in Diderot’s oeuvre.

This historical complexity has given rise to some difficulty inassessing Diderot’s writings according to the disciplinary canonof modern philosophy. Condillac, Helvétius, and d’Holbachare the Enlightenmentphilosophes most commonly studiedwithin philosophy departments because their writings appear to conformbetter with conventional understandings of what philosophy should looklike as a genre and a linguistic idiom. By contrast, the works ofDiderot tend to be studied only in literature or history departments.This is unfortunate, for the treatment of Diderot’sphilosophie as something different from modern philosophy hascut contemporary philosophers off from the work of one of the mostsophisticated, subtle, and complex philosophical thinkers of theeighteenth century.

To some extent, the way in which Diderot’s philosophical workemploys different genres but also, challenges the idea of genreitself, has made it seem (perhaps too easily) congenial to a more“Continental” philosophical tradition, and foreign to amore formally oriented “analytic” tradition. But thatwould ignore Diderot’s naturalistic commitments and the role theEncyclopédie played, e.g., in the self-image ofphilosophers of science in the Vienna Circle. Our entry seeks to gobeyond such oppositions in dealing with Diderot as a philosopher.

Neither perspective alone fully grasps the richness of Diderot’scontributions to modern philosophy, so in order to fully situate hisphilosophie within philosophy writ large, a flexible andreflexive attitude regarding his writings must be adopted. Every textin Diderot’s oeuvre needs to be treated as a participant in bothhisphilosophie and his philosophical work, and ourconventional understanding of the boundaries isolating art andliterature from science and philosophy also needs to be suspendedbecause very often these modern distinctions do not apply inDiderot’s case. He also manifests an awareness of the new andemergent disciplinary taxonomy arising at the time, targeting hisphilosophie on many occasions at an interrogation of thesedeveloping epistemological divisions. This reflexivity often makes histhought even more relevant today than it was when it was written.

To capture the complexity of Diderot’sphilosophie asphilosophy, this article adopts this reflexive approach. It willproceed in two parts. An overview of Diderot’s life and majortexts is offered in Part I so as to present his work and writings asparticular episodes in a coherent eighteenth-century life and career.To simplify the reading of this biography, the text is offered in atwo-level presentation. A short overview of the highlights ofDiderot’s life and work is offered in Section 1 to give readersa schematic overview, but a more extensive presentation of hisbiography is available in theBiographical Supplement. A comprehensive analysis of Diderot’s major philosophicalpreoccupations as revealed in his writings is then offered in Section2 so as to outline the contours of Diderot’s place withinEnlightenmentphilosophie and modern philosophy overall. Thisis followed by brief concluding remarks in Section 3.

• 1. Diderot’s Life and Major Writings
  • 1.1 Years of Formation and Struggle (1713–1749)
  • 1.2 Ascendance as Writer andPhilosophe through theEncyclopédie (1750–1765)
  • 1.3 The Years of Celebrity (1765–1773)
  • 1.4 Twilight Years (1773–1784)
• 2. Major Themes of Diderot’s Philosophy
  • 2.1 Skepticism, eclecticism and language
  • 2.2 Radicalizing empiricism
    • 2.2.1 Empiricism, from epistemology to ontology
    • 2.2.2 Empiricism and experimentalism
    • 2.2.3 An experimental metaphysics
  • 2.3 Materialism, science and living matter
    • 2.3.1 Vital materialism as “modern Spinozism”
    • 2.3.2 Matter theory and living matter
    • 2.3.3 Body and embodiment
  • 2.4 Determinism and change
  • 2.5 Diderot’s philosophical anthropology
    • 2.5.1 Aesthetics
    • 2.5.2 Philosophy of language and representation
    • 2.5.3 Ethics
    • 2.5.4 “Man and world”
• 3. Conclusion
• Bibliography
  • Primary Sources
    • Diderot’s Works
    • Chronology of Writings
    • Other Primary Sources
  • Secondary Sources
    • References
    • Biographies and bibliographical studies of Diderot
• Academic Tools
• Other Internet Resources
• Related Entries

1. Diderot’s Life and Major Writings

Diderot’s long, varied, and eventful life can be presented infour distinct phases:

1. a period of maturation amidst struggle in the 1730s–40s asthe impoverished young Diderot sought to establish himself as a writerin Old Regime Paris through the pursuit of the highly precariousvocation of writing and publishing;
2. a period of intellectual ascent after 1749 as Diderot used the newfinancial stability and intellectual notoriety acquired by editing theEncyclopédie to build a base for his mature career asan Enlightenment writer, critic, andphilosophe;;
3. a period of intellectual celebrity as the new freedom broughtabout by the completion of theEncyclopédie in 1765allowed Diderot to produce some of his most important, if oftenunpublished, work;
4. a twilight period begun in 1773 after his financial burdens werefully eliminated through Empress Catherine the Great of Russia’slucrative patronage, when Diderot brought to completion the widerphilosophical program established earlier, with an additionaldimension of political radicalism.

1.1 Years of Formation and Struggle (1713–1749)

Born to an artisan cutler in 1713 in Langres, a city 300 kilometerssoutheast of Paris, Diderot began his life with very little pointinghim toward his future as a world-renowned writer and intellectual. Hisfirst steps were supported by a university education under thesupervision of the Jesuits and training in scholastic philosophy andtheology through the M.A. level.

Having moved to Paris as a teenager to pursue his studies, Diderotbegan to forge his career as a piece writer in the vibrant buteconomically constrained world of Parisian publishing.D’Alembert would later romanticize the life of the poor butfully independent writer as an ideal to which allhonnêtesgens de lettres should aspire, and Diderot actually lived theimpoverished bohemian writer’s life in the flesh. During the1730s, he struggled continuously to eke out a minimal existencethrough occasional work with his pen, especially finding work as atranslator, and his financial hardship was increased after hismarriage in 1743 to an equally poor woman and the arrival of adaughter soon thereafter.

In the 1740s, poor and still marginal, Diderot began to build thecareer as a writer and intellectual that would make him famous. In1742, he met the young Jean-Jacques Rousseau, a key moment in thegenesis of thephilosophe movement, which Rousseauimmortalized for posterity in hisConfessions. Etienne Bonnotde Condillac also joined their circle at this time. Diderot furtherbegan to write and publish his own books in this period, establishinghis name and reputation as a philosophical author, one who wasperennially associated with the most radical and controversialideas.

Key works from this period include a very loose translation ofShaftesbury’sAn Inquiry Concerning Virtue and Merit,in which Diderot turns moral sense theory into a kind of aesthetics ofNature;Pensées philosophiques, a work of provocativephilosophical propositions concerning matter, motion, nature andscience;La Promenade du sceptique, a philosophical dialoguewhich was written in this period but only published a century later;andLes Bijoux indiscrets, which is best described asphilosophical pornography.

The climax of Diderot’s prolific decade occurred in 1749 withthe publication ofLettre sur les aveugles à l’usagede ceux qui voient, one of Diderot’s masterpieces andarguably his most sophisticated and complex philosophical text afterLe Rêve de D’Alembert andLe Neveu deRameau. TheLettre, which presents itself as a series ofreflections on the blind mathematician Nicholas Saunderson, is perhapsbest described by Diderot biographer Arthur N. Wilson as“disarming” (1972: 97).

Diderot’s public intellectual acclaim increased with each ofthese books, and by the time of theLettre sur les aveugleshe had become famous enough for Voltaire himself, already the publicface of radicalphilosophie, to write to Diderot praising hisbooks. But the same acclaim that attracted Voltaire’s attentionalso rendered Diderot suspicious in the eyes of the Frenchauthorities. A police file with Diderot’s name on it was openedsoon after thePensées philosophiques appeared, andthis work was ordered to be publicly burned in July 1746. By 1749, theevidence pointing to Diderot’s authorship of these subversive(potentially or explicitly atheistic) works was conclusive, and afterthe publication of theLettre sur les aveugles an order wasissued ordering Diderot’s incarceration in Vincennes prison. Hewas imprisoned for three months starting in July 1749, before beingreleased the following November.

1.2 Ascendance as Writer andPhilosophe through theEncyclopédie (1750–1765)

When Diderot was released from prison in November 1749, he was alreadyat work on a new project, the one that would launch him to globalintellectual fame.

Begun in 1745 as a project to publish a complete French translation ofEphraim Chambers’ 1728Cyclopedia, or Universal Dictionaryof Arts and Sciences, theEncyclopédie, arguablythe single most transformative work of the French Enlightenment, hadbecome by 1749 something entirely new. Breaking free of thetranslation agenda, a new work was imagined, to be edited by Diderotand D’Alembert, that would serve as the vehicle promoting thenewphilosophie.

In November 1750, Diderot released a “Prospectus” for theEncyclopédie, inviting readers to subscribe to a newmultivolume compendium. In this preview, Diderot began to reveal hisconception of what theEncyclopédie would become. Nolonger a translation of someone else’s book, and even less astaid compendium of already established learning, Diderot imagined theEncyclopédie as a dynamic site of living thought, anengine for changing, not codifying, existing knowledge. These ideaswere further developed in Diderot’s article“Encyclopédie”, which was published in volume V ofthe work in 1755.

The middle of the eighteenth century has appeared to many as awatershed moment in French intellectual history. As anineteenth-century commentator put it, after this date “writingshostile to religion appeared and multiplied, and a war broke outbetween skepticism and faith” (Wilson 1972: 94–95, quotingan editor of Barbier 1857: vol. 4, p. 378, fn. 1). Whatever the priorpreparation, the launch of theEncyclopédie atprecisely this moment fueled this dynamic, and it quickly provoked awar between its editors and the religious authorities in France. Atthe heart of the struggle were the Jesuits, especiallyGuillaume-François Berthier, who used the Jesuit journal toattack the new encyclopedia project and its editors. Diderot respondedwith pamphlets, and this sparring continued as the first two volumesof theEncyclopédie appeared in print.

The tension with French clerical authorities worsened when theabbé de Prades, a friend of Diderot’s and contributor totheEncyclopédie—he wrote the entry“Certitude”—successfully defended what was laterdeemed to be a theologically suspect doctoral thesis. The controversyled the crown to temporarily suspend the publicationprivilège for theEncyclopédie, butthanks to the favor that Diderot and his partners enjoyed in higherplaces, publication was resumed and Volumes II–VI appearedwithout pause between 1751–1756 even though accompanied byongoing criticism from the Jesuits.

New controversies over theEncyclopédie occurred in1757, although the return of unrest had little overtly to do withphilosophie. The trigger was an attempt on King LouisXV’s life by a house servant named Damiens, who stabbed the kingwith a small penknife. The act of regicide itself was less significantfor theEncyclopédie than the perceived motivation forthe crime, for authorities began to link Damiens’s purportedmadness to the unchecked spread of subversivephilosophie.Provoked by these public fears, French authorities issued new edictscracking down on allegedly subversive books, and new works critical oftheEncyclopédie also appeared, generating the idea ofan “Encyclopedist party” organized for the purpose ofattacking morality, religion and government. When Volume VII appearedsoon after Damiens’s attack, the tinder was therefore set for anew eruption of controversy.

The controversy grew intense, leading D’Alembert to resign aseditor, putting Diderot in sole control of the project. The final blowagainst theEncyclopédie occurred in July 1758 whenClaude-Adrien Helvétius publishedOn the Mind (Del’Esprit), one of the most overtly materialist andheterodox works of the French Enlightenment. Although Helvétiuswas not technically anencyclopédiste, he certainlymoved in the same circles, and his work fit comfortably with theimaginary template of subversive materialistphilosophie thatcrystallized after the Damiens Affair. Accordingly, as the officialsin charge of securing public order, morality, and the booktrade—the three were one in absolutist France—began tocrack down on Helvétius andDe l’Esprit, theEncyclopédie found itself pulled into the courts as asupposed accomplice aiding and abetting its crimes.

Thanks to a secretive ad hoc agreement, however, work on the final tenvolumes of theEncyclopédie was allowed to continue,leading to the full publication of the work in 1765 with each of thevolumes falsely indicating a publication in Neuchâtel as a wayof complying with the royal ban. During the same years, the volumes ofaccompanying plates appeared since they were not subject to the ban,and by 1772 the final volumes of the plates were published toaccompany the seventeen volumes of text that were already in print.With that the entireEncyclopédie was brought tocompletion.

1.3 The Years of Celebrity (1765–1773)

In 1765, after the final appearance of all text volumes of theEncyclopédie, Diderot experienced a kind of liberationas his life was freed from the work that had occupied most of his timeand energy over the previous fifteen years. During the 1760s, Diderotcontinued to do what was necessary to see theEncyclopédie project completed, ultimately authoringnearly six thousand articles himself. But he was also gradually ableto step back, retreating in some respects to the background of thephilosophe movement. With this liberation, a highlyproductive period in his life began as new and original books began toflow from his pen.

Diderot’s earliest writings from this period, pursued while theEncyclopédie project was still ramping up to fullspeed, continued the philosophical and literary explorations initiatedin the 1740s. Taken as a whole they reflect his lifelong preoccupationwith questions of life, liberty, purpose, and order within anEpicurean cosmos that may not be governed by a providential creator,along with his continuing interest in the epistemological problem ofdiscerning the nature and principles of such a world, especially asthey related to the emerging biological sciences of the eighteenthcentury. Key works in this vein includeLettre sur les sourds etmuets à l’usage de ceux qui entendent et quiparlent, a continuation of sorts to hisLettre sur lesaveugles, andPensées surl’interprétation de la nature, a work that retainsthe episodic, propositional structure of hisPenséesphilosophiques while expanding the explanations within eachsection.

Scholars have also suggested, though never proven definitively, thatDiderot contributed during these years to Barond’Holbach’sSystème de la Nature, firstpublished in 1770, a book that stands alongsideHelvétius’De l’Esprit as one of the greatmasterpieces of French Enlightenment materialist philosophy. Diderotwas certainly at the center of the D’Holbach’s coterie,and if the dry and programmatic systematicity ofD’Holbach’s book lacks the lively play of Diderot’sbest philosophical writing, it is certain that he and the Baron werekindred spirits.

One of Diderot’s great masterpieces, written during these yearsbut only published posthumously, should be included as a part of thenatural-philosophical corpus summarized above, even if it engages withthese seminal questions of metaphysics and natural philosophy in anovertly literary manner, drawing more on Enlightenment epistolarynovels and theater for its construction than the classicalphilosophical genres of antique philosophy (although one should recallthat Plato wrote dialogues).

CalledLe Rêve de D’Alembert(D’Alembert’s Dream), the work is in fact atrilogy of dialogues whose centerpiece provides the title. Thiscomplex text reveals some of Diderot’s most important thinkingabout metaphysics as it relates to biology and the life sciences.Although it was never published in Diderot’s lifetime, it wasnevertheless one of his favorite works, and he gave one copy toCatherine the Great as a gift, together, significantly in terms of hisunderstanding of the work, with a set of “Fragments” thathe presented as belonging to his physiological writings. The dialogueswould certainly have been considered a subversive work had they beenpublished when they were written, and whatever Diderot’smotivations in producing it as he did, the creative complexityconverges into what is without question one of the great masterpiecesof Enlightenmentphilosophie.

The same combination of literature and philosophy, textual play andreasoned argumentation present inLe Rêve deD’Alembert is also present in Diderot’s otherseemingly literary and artistic writings, which also contain muchserious science and philosophy.

One important cluster concerns the theory and practice of theater.Diderot wrote scripts for plays that were staged in Paris, includingLe Fils naturel in 1757 andLe père defamille in 1758. These were moralizing melodramas advocating theethical value of the conjugal family and the virtues of thrift,domestic love and piety. His plays are not major touchstones in thehistory of theater, but his meta-theoretical writings about theateritself, which provide many interesting points of departure for hisphilosophy, are important contributions to aesthetic theory.Diderot’s novels and other works of overt fiction also partakein the aesthetic explorations that mark his best work on the theater.In both, Diderot manifests an interest in the nature and limits ofrepresentation itself, and a self-aware consciousness regarding thetenuous interaction between language, experience, and their ability tomerge (or not) into coherent representations. These are issues thatare present in all of Diderot’s most sophisticated thought,including his more explicitly framed philosophy.

Diderot displayed the same philosophical-literary tendencies in hisart criticism. His work in this area began in 1759 when the journalistF.M. Grimm invited Diderot to contribute to his monthly journalCorrespondence Littéraire with reflections on the artdisplayed at the biennial Parisian art salon. Staged in the Louvre,these shows allowed painters and sculptors to showcase their work in asetting that gave a broad public audience access to the work of thebest artists of the day. Others had written commentaries about theexhibitions before, but no one before Diderot had provided anythinglike the critical philosophical assessment of the art of thesalons.

A new academically centered art theory had developed in theseventeenth century, and by 1700 it was joined by a new persona, theconnoisseur, who was helping collectors to hone their judgment whenseparating truly great art from mere craft. The bi-annual Parisiansalons had already become a site of Enlightenment aesthetics andconnoisseurship by 1750, yet before Diderot no one had broughttogether the job of the connoisseur and the aesthetician with that ofthe public writer reflecting on art in relation to ordinary humanexperience. In his “Salons”, as they came to be called,Diderot brought all of these agendas together into one discursiveprogram, inventing as a result a new identity: the art criticsustained through contemporary art criticism. The result was also anew and pioneering notion of philosophy of art.

Diderot’s art criticism explored exactly the same dynamicsbetween form and content, author and interpreter, subject andobject—in short, the very problem of artistic representationitself—that his theater, his fiction, and his philosophyexplored as well. The result was a general understanding of aestheticsand its relationship to ethics that was integrally connected to hisphilosophy overall.

Diderot’s art criticism joined with his theater criticism, hisprose and other theoretical writings in offering readers reflectionson deep metaphysical and epistemological questions concerning thepower and limits of representation. From this perspective, it isappropriate that arguably Diderot’s greatest and mostinfluential text is at once a literary fiction, asemi-autobiographical psychological memoir, a theatrical send-up ofParisian society, an intimate portrait of contemporary social mores,and a highly original and complex study of the nature of humanperception, being, and their interrelation.

CalledLe Neveu de Rameau, the text ostensibly narratesDiderot’s meetings and conversation with the nephew of theFrench composer Jean-Philippe Rameau. Yet the dialogue unfolds througha back and forth between characters named “Moi” and“Lui”, or me and him, continually turning a discussionbetween two discrete subjects into an inner monologue of one subjectdialoguing with himself. Indeed, as the exchange carries on, the twocharacters are revealed to be different sides of a deep existentialdialectic. At this point the external reality of the characters beginsto dissolve, and “Moi” and “Lui” start tobecome two competing principles within an intractable universalethical and metaphysical struggle.

Diderot did not publishLe Neveu de Rameau in his lifetime,but the text found its way to Germany where it was read by Schillerand Goethe. Goethe’s German translation, published in 1805, wasa major influence on Hegel: theNeveu is the only modern workexplicitly cited in his 1807Phenomenology of Spirit. Indeed,its influence on the formation of Hegel’s own dialecticalunderstanding of metaphysics and the nature of being is patent, and aline connects Diderot and theNeveu with all subsequentmetaphysical understandings of the self as a singularity caught in aconstant struggle with universal forces pulling the unity of beingapart.

1.4 Twilight Years (1773–1784)

Further helping Diderot after 1765 was the generosity of Catherine theGreat of Russia, and his trip to her court in St. Petersburg in 1773marks the passage of Diderot into the final stages of his career.

Catherine watched the development of theEncyclopédieproject with great interest and expressed affection for FrenchEnlightenmentphilosophie overall. Fate provided her with anoccasion to express her appreciation directly to Diderot when afinancial burden forced him to sell his library. Catherine made thepurchase, giving Diderot an annual pension in addition. This made hima wealthy man for the rest of his life. Diderot traveled to St.Petersburg to meet with Catherine in 1773–74, and this tripmarks his entrance into a leisured retirement in Paris where hecontinued to write.

Diderot’s last writings continued themes pursued throughout hislife, but one new interest was history. HisEssai sur lesrègnes de Claude et de Néron, which turned interestin ethics and morality toward questions of politics, justice, andhistory, was one result, as were his contributions to the finaledition of the abbé Raynal’s massive, nineteen-volumeglobal history entitledHistoire philosophique et politique desétablissements et du commerce des Européens dans lesdeux Indes.

The latter was produced by Raynal in a manner similar to theEncyclopédie, with numerous authors contributing. Theresulting work was a pioneering world history defined by its argumentthat the transformations triggered by the Colombian Encounter were thedecisive agent of world historical development. Diderot’scontributions included explorations of the role of commerce, conceivedas an autonomous natural-historical force, in the shaping of politicaland social change, a theme that connects Diderot’s writing withthe new sciences of Enlightenment political economy. The Atlanticslave trade also attracted his attention, and some of his mostpassionate contributions involve imagined dialogues about the horrorsof the European imperial slave system spoken by oppressed Africans.Raynal’sHistoire was a massive bestseller, translatedinto many languages, and it was a direct influence on Hegel, Marx, andthrough both on modern world history more generally. Diderot’scontribution to this influence was as important as any.

Diderot’s contributions to Raynal’sHistoire havebeen described as proto-anthropological, and another provocative workfrom these years, hisSupplément au voyage deBougainville, was similarly conceived and influential. The textoffers an imagined dialogue between Tahitians and Europeans about thedifferent sexual, marital and familial mores of the two cultures, andDiderot anticipates through fiction the figure of the nativeethnographer who asks comparative questions about the foundations ofmorality and civilization so as to generate universal culturalunderstandings through comparison.

In these texts, and others from these years such as hisObservations sur le “Nakaz”, a commentary onCatherine’s Enlightened reform program for Russia, Diderotappears in a newly radical political guise as an aggressiveegalitarian and democrat who has little patience with traditionaljustifications for hierarchy and top-down distributions of power. Heis also a passionate abolitionist with no tolerance for the crimes ofthe Atlantic slave trade. Nature does not work through hierarchy,Diderot insists in these texts, and connecting politics with hisnatural philosophy he argues for a radical decentralization ofpolitical authority, and a fully bottom-up, egalitarian understandingof social order. These convictions are also manifest in his thinkingabout race and slavery. He rejected altogether the new anthropologypromulgated by Kant and others that spoke of biologically andcivilizationally distinct races, offering instead a monogeneticunderstanding of humanity where difference was a matter of degreerather than kind. Diderot was by nature a writer and thinker, not apolitical activist, and his political philosophy, while suggestive ofemerging radical political trends, appears as the least developedaspect of his thought.

When revolution erupted in France in 1789, the memory of Voltaire andRousseau led to their inclusion in the pantheon of revolutionaryheroes worthy of immortal commemoration. Diderot, by contrast, was atbest forgotten and at worst treated as a figure hostile to the newpolitical movements afoot.

This combination of neglect and outright hostility pushed Diderot tothe margins of French culture in the nineteenth century, and it wouldtake another century before retrospective interest in his work wouldbe renewed. Too systematically committed to his materialism, toovigorous in his irreligion, and too passionate and principled in hisembrace of egalitarianism and universal democracy to be acceptable toanyone with the slightest worry about the rising tides of radicalsocialism and materialist freethought, Diderot became a pariah formany in nineteenth-century France and Europe. Only after 1870 wasinterest in his work revived, thanks in part to the new editions ofhis writings, which made him newly available to scholars and readers,and to the changing cultural and political climate. Soviet Marxists,for example, played a key role in reviving Diderot scholarship after1900, and contemporary Diderot studies, which is thriving today, islargely a twentieth-century creation. Literary scholars led the way inestablishing the contemporary scholarship, but recently scholarsattuned to the very different character of philosophy and science inthe eighteenth century have begun to return to Diderot’s work,finding in it the complex and sophisticated thinking that was hishallmark.

Diderot is now actively studied by both literary scholars andintellectual historians alike, and there was even a movement afoot asrecently as 2013 to enshrine Diderot alongside Rousseau, Voltaire, andCondorcet in the Panthéon of French national heroes. Headlinesworrying about “un homme dangereux auPanthéon?” revealed the continuing influence of hisalleged infamy, yet the twenty-first century may be the moment whenDiderot is finally recognized as the important eighteenth-centuryphilosopher that he was.

For a more complete biography of Diderot, see theBiographical Supplement.

2. Major Themes of Diderot’s Philosophy

There are different ways of dividing up Diderot’s intellectualcareer, some which emphasize pure philosophical commitments, othersfocusing on particular projects or strands of his thought, and stillothers giving pride of place to politics. Of course, all of themacknowledge the central place of theEncyclopédie, notjust because it was an enormous editorial project spanning many of the“best” years of Diderot’s productive life, butbecause it marked the invention of a new model of knowledge,collaborative in the literal sense as a compendium of individuallyauthored articles, but also in the sense of joining disciplines,including the “arts and crafts”, as newly equal purveyorsof theoretical knowledge along with “first philosophy”.TheEncyclopédie is also an important resource if oneis looking for Diderot’s sources, as he authored many longentries on Epicureanism, Hobbes, Locke, Leibniz, or ratherLeibnizianism, along with texts on eclecticism, skepticism and otherdoctrines which reveal both his involvement with such ideas and theway he transforms them.

2.1 Skepticism, eclecticism and language

Aside from the early translation projects discussed in Part I,Diderot’s first philosophical writings, such as thePensées philosophiques (1746, expanded in 1762) andthePromenade du sceptique (1747), play a complicatedrhetorical game with deism (rather than overt materialism),skepticism, and natural religion. In thePensées,Diderot even toys with a “design argument” using theclassic example of the complexity of a butterfly’s wing (§XVIII), although he seems to retract this a few years later, in theApologie de l’Abbé de Prades (1752), writingthat “I thought the wing of a butterfly brought me closer todivinity than a volume of metaphysics” (DPV IV: 361,translations always ours unless otherwise indicated). Even if he isnot yet a materialist in these works, Diderot does speak of thenecessity to “widen” or “enlarge” God(Pensées philosophiques, § XXVI), a phrase whichhas fairly strong Spinozist and/or deist overtones.

By the time of theLettre sur les aveugles (1749), Diderothas launched upon a philosophical project, or a set of intersectingprojects, which will endure to the end of his life: a radicalizationof empiricism in the direction of a materialist metaphysics, whichalso remains at times skeptical or at least anti-foundationalist withregard both to the possibility of an intellectual system, and to theexistence of order or totality in the universe.

Yet if Diderot’s philosophy needs to be understood in terms ofhis lifelong project to develop and refine certain clear metaphysicaland epistemological commitments and arguments, it also needs be tounderstood in terms of his avowed “eclecticism”, inparticular his hostility to overly binary dogmatic thinking. Thisreflects his deep awareness of the complexities of language itself,especially the immanent tendency for speech to refute itself andsubvert its stated convictions. Diderot’s passionate love forirony, satire, humor, and the play of language as both a critical andsubversive force often served him as a vehicle for capturing theinfinite complexities of being that transcend stable finite humanunderstanding, which means we his writing should also be read with thesame attention to its linguistic complexity that he had when writingit.

Although the link it is not often noted, it is useful in this contextto remember that Diderot was among the generation of Frenchphilosophers that were directly influenced by NicolasMalebranche, whose influence upon French philosophy in the years 1690–1730,the precise years of Diderot’s maturation as a thinker, wasimmense and insufficiently recognized. This influence was not rootedin Malebranche’s specific doctrines such as occasionalism, butin the model his philosophy offered of how empirical skepticism couldbe sustained together with scientific, and especially mathematicalrationalism. Diderot’s own affection for mathematics was rootedin these Malebranchian currents of French thought, as were his strongconvictions about the limits of mathematics as well.

Malebranche’s philosophy has aptly been described as“Hume, but with Christian faith” in the sense that likeHume he offers a massive skeptical critique of the capacity for humansto produce certain knowledge as a result of the epistemologicalinadequacy of their senses and higher cognitive faculties, but unlikehim Malebranche nevertheless offers a path forward toward suchknowledge through a Cartesian understanding of divine reason asaccessible to humans through the proper practice of mathematicalreasoning. In brief, to reason like God is to reason like an advancedmathematician, especially one trained in the new analyticalmathematics of the period, and to the extent that this kind ofreasoning is adaptable to human language itself, it allows for humanthinking to connect with the divine order of things through a properpractice of rigorous cognitive and linguistic discipline. Anchoringthis understanding for Malebranche was a Christian faith in arationally created cosmos accessible to the human mind, and whilelater Malebranchians followed Hume in discarding this Christianfoundation, many nevertheless absorbed Malebranche’s lessonsregarding the power of a properly constituted language (his model wasadvanced analytical mathematics) to serve as a bridge connectinglimited humans with the infinitude of being. Diderot’s partnerD’Alembert represented the explicitly mathematical strand ofthis tradition of thinking, but Diderot embodied another strand, moreattentive to language in all its variety as the link joining finitehuman understanding with the infinite complexities of nature. AlthoughDiderot was suspicious of D’Alembert’s Malebranchianconception of mathematics as the foundational model for all ofscience, his own interests in the empirical natural sciences werestill rooted in the same preoccupation with how nature representsitself and is represented by humans in scientific work. He wasespecially attentive to the crucial role that language plays inrendering experiential phenomena suitable for human knowledge, and ifhe was critical of the over-emphasis upon mathematics as the suprememodel for a fully rigorous scientific language, he was neverthelessMalebranchian in treating the relation between experiential phenomena,linguistic description, and human knowledge in all its variety as theepistemological zone that mattered most.

Diderot’s eclecticism from this perspective was not simply anegative reaction against dogmatism, even if in his importantEncyclopédie article “Éclectisme”,he opposes eclecticism to sectarianism. He also explicitly tieseclecticism to an attention to language and discursivity inphilosophy. Founders of discursivity are eclectics, distinct fromsyncretists (Diderot mentions Luther and Bruno as examples). However,he fully disapproves of the Alexandrian school of eclectics, whileattaching himself tomodern eclecticism (includingCampanella, Hobbes, and Bacon, but also Descartes, a reference thatmakes most sense if read through Malebranchian Cartesianism):“The eclectic does not randomly gather together truths, norleave them in isolation; even less does she force them into somedeterminate plan” (Enc. V: 270). Diderot presents bothBacon and Descartes as eclectics, which we might actually think of asmeaning “empiricists”, in the sense of placing experienceand experiment at the center of knowledge-gathering practices. But weshould also see this in terms of language, remembering the linkbetween Montaigne and his project of representing natural experiencethrough his new genre of the essay, and Bacon’s own attachmentsto empiricism, experimentalism, and the genre of the essay, along withother forms of representational writing, including fictionalstorytelling and the use of aphorisms alongside other morerecognizable philosophical genres.

Diderot’s eclecticism and materialism nevertheless remain intension, since eclecticism is not conducive to foundationalontological commitments, while materialism, whatever the specificmatter theory it bases itself on, seems to be a paramount case of afoundationalist ontology. What is real is matter, or perhaps, what thesciences of matter declare to be real (and this can vary widely, fromthe chemistry of mixts which Diderot was so fascinated by[Pépin 2012], to the nascent biology he seems to be calling forin thePensées sur l’interprétation de lanature, as we discuss below, to physics). And yet, as a series ofpropositionalpensées offered to readers without anyinterconnecting discursive bridge between themes, this text alsopropounds eclecticism methodologically, in contrast to asystematically presented set of premises, arguments and conclusions.This play between imaginative possibility and demonstrative certainty,and between what rationally must be and what language is capable ofcapturing and conveying in human terms is characteristic ofDiderot’s thought overall, and his philosophy cannot be shorn ofthis conceptual linguistic instability without destroying itspower.

In the next three sections, we discuss his empiricism, his materialismand what we term his philosophical anthropology, namely, his ideasconcerning features specific to human beings, such as aesthetics andethics, although as we discuss, these are also located withinDiderot’s overall commitment to naturalism.

2.2 Radicalizing empiricism

2.2.1 Empiricism, from epistemology to ontology

Diderot is heavily influenced by Locke and in general by a kind ofempiricism that was “in the air”: our knowledge about theworld is derived, either fully or at least in large part, from oursenses. In theLettre sur les aveugles and its companionpiece, theLettre sur les sourds et muets, as well as laterpieces such as theRêve, Diderot turns the question ofthe senses and how we know the external world on its head: the sensespossess or carry with them their own respective metaphysics. It is apowerful kind of relativism. And there is a new hierarchy in whichtouch is fundamental, in direct opposition to classical philosophicaldoctrines in which sight received that honour: throughout his work,but especially in these two essays devoted to the metaphysics of thesenses and his various aesthetic writings, Diderot insists on theprimacy of touch, which he also describes as “the mostphilosophical of senses”; he deplores the fact that “thehands are despised for their materialism” (LSM; DPV IV:15, 54). This is even given atheist overtones in theLettre surles aveugles when the blind mathematician Saunderson on hisdeathbed declares that “if you wish me to believe in God, youwill have to make me touch him” (DPV IV: 48).

Diderot expresses his materialism in this work through the characterof a blind man, also because he is like a living counterexample to theargument from design. Indeed, Saunderson says to his interlocutor, whois defending physico-theological design and order: “What did wedo to God, you and I, so that one of us possesses this organ (ofsight), and the other of us is deprived of it?” (DPV IV: 63). Ina further twist, Diderot also equates the blind man with idealistmetaphysics since it is also cut off from direct sensory engagementwith the world. Here, empiricism is no longer just a doctrine aboutthe sources of knowledge, i.e., an epistemology. The world of a blindman is different from that of a deaf man, and so forth. Further, anindividual who possessed a sense in addition to our five senses wouldfind our ethical horizon quite imperfect (DPV IV: 27).

A similar displacement of the “scope” of empiricism occursin the companionLettre sur les sourds et muets, with arather different version of Condillac’s thought experiment ofthe statue:

My idea would be to decompose a man, so to speak, and examine what hederives from each of the senses he possesses. I recall how I was onceconcerned with this sort of metaphysical anatomy, and had found thatof all the senses, the eye was the most superficial, the ear the mostproud, smell the most pleasurable, and taste the deepest, mostphilosophical sense. It would be a pleasant society, I think—onecomposed of five people, each of whom only possessed one sense. Theywould undoubtedly call each other mad, and I leave you to imagine howright they might be. Yet this is an image for what happens toeveryone: one only has one sense and one judges on everything. (DPVIV: 140)

The senses here are treated as producing “worlds” in whichwe live, not as epistemological sources of knowledge, which was thestrict issue raised byMolyneux’s Problem (if a person born blind, with an understanding of basic mathematics,recovered their sight and saw a cube, would they instantly know whatit was?), a problem that goes through considerable reconfigurationwith the character of Saunderson.

2.2.2 Empiricism and experimentalism

Empiricism is further transformed by Diderot in accordance with hisproject to transform knowledge by inscribing it in the sphere ofpractice and “arts and crafts”, especially with theEncyclopédie. He sometimes refers approvingly to themanual labourer (manouvrier)’s production of anartisanal knowledge, notably in his 1753Pensées surl’interprétation de la nature (§ XXX), whichnot coincidentally sounds Baconian and Lockean. But more surprisingly,he also equates this transformed, even “enhanced” visionof empiricism with a metaphysics. That is, on the one hand he is anempiricist advocating the experimental sources of new knowledge,sometimes presented as “experimental philosophy”:

Experimental philosophy does not know what its work will yield or failto yield; but it works without pause. On the contrary, rationalphilosophy weighs the possibilities, makes pronouncements, and stopsthere. It boldly declares,light cannot be decomposed;experimental philosophy listens, and remains silent for centuries;then suddenly shows us the prism, and declares,light isdecomposed. (IN, § XXIII; DPV IX: 43–44; hisemphasis)

We can also see this anti-foundationalist and experimentalist attitudeas challenging Descartes’ “chains of reasons” whichextend to all our knowledge of things; Diderot begins the above workby explaining that he will let his thoughts follow the order in whichobjects presented themselves to his reflection (§ I). Such a viewis also resonant with what we might term Malebranche’squasi-sensationalism, which locates scientific thinking in thereduction of our stream of sensate observations to the rationalizinglogics of mathematical analysis, if we consider that, aside from the“occasionalism” which has dominated his Anglophonereception, much of Malebranche’sRecherche de laverité is about how our bodily passions and our sensationsproduce errors in us, which makes Malebranche a sensationalist inrecognizing that conception of the human subject as the start for anyepistemological project of knowing. Diderot, from theLettre surles aveugles on, is a dedicated empiricist and sensationalist,although he expands the remit of these philosophical programs farbeyond “epistemology”.

But on the other hand, Diderot treats the idea of experimentalphilosophy rather playfully, both endorsing it and going beyond it ina more speculative direction, as when he mockingly refers to themathematician’s self-confident rejection of metaphysics bywriting, “the metaphysician … is someone who knowsnothing”, and comments that

chemists, physicians, naturalists and all of those engaged inexperimental practices (l’art expérimental)… seem to me to be on the point of avenging metaphysics, andapplying the same definition to the mathematician (IN, §III; DPV IX: 29–30)

avenging metaphysics, in the sense of turning the charge of beingoverly speculative back at the scientists!

2.2.3 An experimental metaphysics

Sometimes the empiricist and the metaphysical tendencies areencapsulated in a single formulation, as in the “experimentalmetaphysics” in theBijoux indiscrets, by which hemeans an experience-based metaphysics, building up from the fact that“all is experimental in us” (SA; DPV XVI: 87);this formulation does not mean that we are the result of an endlessseries of trial and error attempts, but that all results fromexperience.

In hisEncyclopédie article“Métaphysique”, Diderot also opposes an abstractmetaphysics of time, space and being to a practice-based metaphysics:he suggests that practitioners such as musicians and geometricians beasked about the “metaphysics of their art”, which willyield promising results, just as in thePensées surl’interprétation de la nature he lauded the figurehe described as the “manouvrierd’expérience”, a kind of artisan-experimenter whosepractice has yielded, over years of experience, an artisanalknowledge.

Contrary to a now-common idea that the opposition between rationalismand empiricism should be replaced with a more historically legitimateopposition between experimental philosophy and speculative philosophy(Anstey 2005), Diderot’s case suggests a blend betweenempiricismcum experimentalism, and speculation. He is oftenconfronted with the need to continue his analysis of phenomena beyondthe limits of strict empiricism: the nature of matter, the limits ofanimation or on the more internal scale, the functioning of thenervous system or the mechanics of generation. And here the need formetaphysical imagination comes into play, which is not the same as astrictly abstract metaphysics. Once again, Diderot’s criticismsof mathematical abstraction in favor of the greater concreteness ofthe life sciences, which he shares with Buffon, can be adducedhere.

2.3 Materialism, science and living matter

Diderot was not a physician like La Mettrie, or a “workingnatural historian” like Buffon, although at one point he wrotethat, “It is very hard to do metaphysics or ethics well, withoutbeing an anatomist, a naturalist, a physiologist, and aphysician” (RH; DPV XXIV: 555). Nevertheless, one ofhis first publications was the translation of James’Medicinal Dictionary (1745), and in addition to his enormousactivity as the chief editor of theEncyclopédie,which heavily features medical entries, sometimes with his editorialinterventions, he was also a serious student of chemistry, including“vital chemistry” (Pépin 2012). Later in life hedeclared that “there were no books I read more willingly thanmedical books” (EP; DPV XVII: 510).

Given this background, Diderot’s interactions with the lifesciences of his time can be understood, obviously, as the activity ofan educated individual with a strong interest in the implications forphilosophy of new scientific discoveries and conceptual schemas,whether from medicine, biology, or natural history. But hisarticulation of all of these in amaterialist project doesnot belong to or open onto an episode amongst others in the history ofscience. That is, his articulation of a unique kind of philosophicalmaterialism is indeed in “dialogue with” or“influenced by” the sciences of his time, particularly thelife sciences (which included chemistry for Diderot), but it is also aspeculative project; materialism in Diderot’s time, like inours, was not a monolithic concept (Springborg and Wunderlich [eds]2016).

2.3.1 Vital materialism as “modern Spinozism”

Diderot opposed the novelty and conceptual significance of the lifesciences to what he (incorrectly) judged to be the historicalstagnation of mathematics:

We are on the verge of a great revolution in the sciences. Given thetaste people seem to have for morals,belles-lettres, thehistory of nature and experimental physics, I dare say that before ahundred years, there will not be more than three great geometriciansremaining in Europe. The science will stop short where the Bernoullis,the Eulers, the Maupertuis, the Clairauts, the Fontaines and theD’Alemberts will have left it…. We will not go beyond.(IN, § IV; DPV IX: 30–31)

Similarly, in a letter to Voltaire five years later (February 191758), he wrote clearly that “The reign of mathematics hasended. Tastes have changed, in favor of natural history andletters”. Diderot is opposing the new “taste” andinterest for a set of preoccupations including two forms of“life science” (natural history and “experimentalphysics”) to the traditional prestige of mathematical science.In these passages, he is also squarely locating his materialistpreoccupations within the former.

Diderot’s natural philosophy is deeply and centrally“biologistic”. As it emerges in the mid-eighteenthcentury, at a time before the appearance of the term“biology” as a way of designating a unified science oflife, his project is motivated by the desire both to understand thelaws governing organic beings and to emphasize, more philosophically,the uniqueness of organic beings within the physical world as a whole.Consider a little-known aspect of Diderot’s articulation of hisproject: his statement in favour of biological epigenesis within hisshort entry “Spinosiste” in theEncyclopédie. The entry does not bear his name, butlarge parts of the content occur elsewhere in his writings, and it isincluded in all editions of his works. Here he grafts new biologicalideas such as epigenesis onto a Spinozist substance metaphysics (Wolfe2014a), distinguishing between “ancient” and“modern” Spinozists and emphasizing that the latterspecifically hold that “matter is sensitive”, asdemonstrated “by the development of the egg, an inert body whichby means of heat alone moves to the state of a sensing, livingbeing”. For modern Spinozists, “only matter exists, andthat it is sufficient to explain everything. For the rest, they followancient Spinozism in all of its consequences” (Enc. XV:474).

Diderot is rather unexpectedly combining Spinoza’s metaphysicsof substance with a new theory of biological development, epigenesis,according to which the embryo grows by the successive addition oflayers of purely material substance. Why call the latter view“modern Spinozism”? The “ancient Spinozists”are substance monists and metaphysicians, while their moderndescendants are also committed to biological epigenesis, and assertthat matter is fundamentallyliving matter. Is this Spinozismor not? What possible relation could there be between Spinozism andepigenesis? Or how can a metaphysics of substance and modes, whichsays almost nothing about biological entities even if it is also amajor statement of philosophical naturalism, also be a fashionableembryological theory of the seventeenth and eighteenth centuries? Infact, very few commentators have askedwhy Diderot gives suchan idiosyncratic definition of “modern Spinozism”.

To be sure, his convictions regarding living matter (or all of matterinasmuch as it is potentially living and sensing) are tied to hisadmiration for the metaphysics of a single substance composed of aninfinite number of modes. As he states in theRêve deD’Alembert, “There is only one substance in theuniverse” (DPV XVII, 107; Wartofsky 1952/1979, Deprun 1986,Bourdin 2008). But nowhere does Spinoza seek to connect hismetaphysics to the life sciences; even if the notion of the conatuswas frequently taken up in the generations after him to mean somethinglike a survival impulse in living beings, this was not what he meantat all. Diderot is grafting “vitalist” elements onto asubstance metaphysics, or at least, he is connecting an apparentlyempirical account of theself-organisation of matter with anew metaphysics. Epigenesis is not just one biological theory amongothers here, but rather, part of a revised metaphysics of matter,which Diderot presents in more overtly ideological terms in theRêve:

Do you see this egg? With this you can overthrow all the schools oftheology, all the churches of the world. What is this egg? Anunsensing mass, prior to the introduction of the seed[germe]; and after the seed has been introduced, what is itthen? Still an unsensing mass, for the seed itself is merely an inert,crude fluid. How will this mass develop into a different [level of]organisation, to sensitivity and life? By means of heat. And what willproduce the heat? Motion. (DPV XVII, 103–104)

Matter for Diderot is self-organizing and endowed with vitalproperties. This implies that his brand of materialism is notsynonymous withphysicalism (admittedly, not a term or notion of the period). There were ofcourse materialists such asHobbes who can also be described as physicalists, but Diderot was quiteexplicitly a determinist, as we will discuss below (insection 2.4). This leads to two rather original consequences, which we examine inthe following sections: Diderot’s metaphysics of vital matter isnot strictly experimentally based, it is also speculative; and his isa specificallyembodied materialism.

2.3.2 Matter theory and living matter

In the very first paragraph ofLe Rêve deD’Alembert, the character D’Alembert, who is apartisan of substance dualism and is challenging the characterDiderot—a materialist—to account for the existence ofconsciousness and thought, introduces the problem of sensibility(sensibilité, better translated“sensitivity”) as a property. Referring to a discussionthat seems to have occurred before the text begins, he declares toDiderot, “this sensitivity … if it is a general andessential quality of matter, then stones must sense” (DPV XVII,90). Diderot states, revises, emends and restates this materialism ofliving, sensing matter in a variety of works, both in theRêve and in his more “empirically” orientedwritings such as thePrincipes philosophiques sur lamatière et le mouvement and theEléments dephysiologie.

Later, building on an explicitly chemical matter theory, Diderot willdescribe nature as perpetually “in action and reaction;everything being destroyed in one form and recomposed in another;sublimations, dissolutions and combinations of all kinds”, inthe “general movement or rather fermentation of theuniverse” (PPMM; DPV XVII: 17–18). This shortpiece of “philosophy of physics” includes a polemic aimedat all those who define matter as inert and homogeneous (latter-dayCartesians). Diderot wants to establish in contrast that motion isinherent in matter by joining together translation andnisus.Indeed, matter possesses properties including sensitivity.

The key property of living matter, and of all matter potentially, isorganic sensitivity. Diderot often suggests that “sensitivity ortouch is common to all beings”, and he often attributessensitivity to matter as a whole (EP; DPV XVII: 308). In“Leibnizianisme”, he brings together Aristotle’sentelechy, Leibniz’s monads, and sensitivity as a “generalproperty of matter” (Enc. IX: 371); indeed, Leibnizianmetaphysics and theories of generation had a great impact oneighteenth-century thought, and has been viewed as major influences inthe formulation of Diderot’s materialism, albeit in naturalizedform, e.g: “the monad, the real atom of nature, the true elementof things” (Enc. IX: 374a). Elsewhere, such as the 1765Letter to Duclos, Diderot denies that sensitivity can be a property ofa molecule, specifically because it can only be a property of matteritself. He then complicates the issue further by introducing adistinction between “inert” sensitivity and“active” sensitivity.

Nevertheless, Diderot’s matter theory is very much one of aliving, sensing, self-transforming matter, sometimes specified inchemical terms:

You can practice geometry and metaphysics as much as you like; but I,who am a physicist and a chemist, who take bodies in nature and not inmy mind, I see them as existing, various, bearing properties andactions, as agitated in the universe as they are in the laboratorywhere if a spark is in the proximity of three combined molecules ofsaltpeter, carbon and sulfur, a necessary explosion will ensue.(PPMM; DPV XVII: 34)

The critique of mathematical abstraction in favor of a moreempirically rich matter theory, whether this is presented as derivingfrom natural history, chemistry, medicine, physiology or otherdisciplines, is also a constant in Diderot. The point we wouldemphasize most, however, is that this is also aspeculativemetaphysics. The shift from inert to active sensitivity is notexperimentally grounded. That Diderot’s materialism was notstrictly an outgrowth of empiricism, and/or experimentally based, asone might expect given the usually close relation between scientificpractice and materialist philosophy, is also apparent in thedimensions he sometimes is willing to allow to his cosmogony ofuniversally living matter.

On one occasion, he wrote to Sophie Volland describing how such ideasled him to be teased, but he pushes them even further in the letter,in the direction of a materialist account of love. The result is notso much a reductionist explanation of the phenomenon of love as aromanticization of materialism itself:

The rest of the evening was spent teasing me about my paradox. Peoplegave me beautiful pears that were alive, grapes that could think. AndI said: Those who loved each other during their lives and arrange tobe buried next to one another are maybe not as mad as one thinks.Their ashes may be pressed together, mingling, uniting. What do Iknow? Maybe they have not lost all feeling, all memory of their priorstate. Maybe they have a remainder of heat and life, which they enjoyin their own fashion, at the bottom of the cold urn in which theyrest. We judge the life of elements by the life of crude aggregates.Maybe they are entirely different entities…. When the polyp isdivided into a hundred thousand parts, the primitive, generationalanimal is no longer, but all of its principles are still alive. O mySophie, I then still have a hope of touching, sensing, loving, seekingyou, uniting and melding with you, when we are no longer. If therewere a law of affinity amidst our principles, if we were entitled tocompose a common being; if, in following centuries, I were to comprisea whole again with you; if the molecules of your dissolved lover wereto stir, to move about, and search out yours, scattered throughoutnature! Grant me this chimaera. It is sweet to me. It would ensure myeternity in you and with you …. (letter of 15 October 1759,translation C. Wolfe)

This image of a kind of eternity in which “lovingmolecules” gradually return to one another, impelled by aresidual consciousness of the love present in their “parentbodies”, resonates with the powerful rendition he gives in thefirst dialogue of theRêve of the thought experiment ofthe statue. Recall that the character D’Alembert had challengedthe character Diderot to show that matter could think, and the latterhad retorted that if he could show that matter could sense thesolution would be found. The character Diderot then proposed a thoughtexperiment of a marble statue, ground into powder, mixed into theearth, out of which plants grow that are eaten by animals who are inturn eaten by us. He calls this process the“animalization” of matter. Thus framed, the differencebetween a piece of marble and a sensing, conscious creature is only adifference in the temporal stages of a portion of matter intransformation. Unlike Condillac’s statue, Diderot’s is nolonger a strictly epistemological account of the genesis of ourknowledge (and self-consciousness) through the accumulation ofintermodal sensory information. Instead, it is an assertion of theanimalization of inert matter, such that all matter is either actuallyor potentially alive.

2.3.3 Body and embodiment

But what of actual bodies in this universe of living matter?Diderot’s notion of body is quite different from, say, that ofDescartes and Hobbes. “As a physicist”, Diderot writes,“one should never saythe body qua body, because thisis no longer physics, it is making abstractions which lead tonothing” (PPMM; DPV XVII: 16). As he wrote to SophieVolland, “Have you ever thought seriously about what it is tolive? … Life is not just motion, it is something else”(letter of 15 October 1759). Indeed, he may quite fairly be describedas a theorist of embodiment.

His materialist notion of embodiment means that Diderot does notoppose the living body as a kind of subjectivity to the world ofmatter overall. As is particularly apparent with Saunderson in theLettre sur les aveugles and the account of the nervous systemin theRêve de D’Alembert, Diderot “pit[s]the unity of sensibility against a Cartesian unity ofsubjectivity” (Gaukroger 2010: 416). However, this emphasis onembodiment is neither a “top-down”, emergent view of life(even if “life is not just motion”), nor anantireductionist position (contrast Kaitaro 1997). For Diderot,emphasis on the features of the living body and a deflationary and/orreductionist attitude go hand in hand. “The action of the soulon the body is the action of one part of the body on another”,he writes, “and the action of the body on the soul is again thatof one part of the body on another” (EP; DPV XVII:334–335). This was certainly reductionist in the eyes ofdefenders of an immortal and/or immaterial soul, but it is not per seeliminativist inasmuch as Diderot is saying that“mental processes” (if we take the language of“soul” here to be psychological language) are bodilyprocesses, not that they are illusory or otherwise unreal. Similarly,commenting on the Dutch scientist Franz Hemsterhuis’ manuscript,he notes: “wherever I readsoul I replace it withman oranimal” (DPV XXIV: 340). This is avenerable trait of materialisms going back at least as far asLucretius, and Diderot does not necessarily deploy this tradition todeny the existence of the soul, but rather to challenge the“animist” or the “idealist” claim “toexplain anything without the body” (EP; DPV XVII: 334).Even more interestingly, this shift can also be seen in broader termsas a shift withinreductionist strategies, which we can alsoclassify astypes of reduction.

One strategy for the early modern materialist was to deny theexistence of a “higher-level” entity such as the soul (orfree will, or thinking, etc.) in favor of a hypothetical “basicphysics” or the properties of matter in general. Thus La Mettriewrote, in his 1748L’Homme-Machine, that

The soul is just a pointless term of which we have no idea and which agood mind should only use to refer to that part of us which thinks.Given the slightest principle of movement, animate bodies will haveeverything they need to move, feel, think, repent and in a word,behave in the physical realm as well as the moral realm which dependson it. (La Mettrie 1987, vol. I: 98)

In contrast, another strategy is to construe “soul” infunctional terms, as not conflicting in any way with a basicmaterialist ontology, if it is not a substance of its own. Thus thematerialist could be less overtly confrontational towards the conceptof soul. For instance, because it has been naturalised, the soul canbe treated, as La Mettrie suggests, as “but a principle ofmotion or a material and sensible part of the brain” (La Mettrie1987, vol. I: 105). Here, as in Diderot, the status of the soul isdisplaced away from metaphysics towards the particular physiologicalsite of the brain. Diderot’sEléments dephysiologie, as well as his supplementary remarks in the article“Âme”, stress both the complexity of the brain forany reductionist materialist project, and the“displacement” of the soul therein. The concept of thebody which is at work in these materialist texts is, if not“ensouled”, certainly animated and vitalised, as in thisremark of Diderot’s:

Whatever idea we initially have of [the soul], it is necessarily amobile, extended, sensitive and composite entity. It grows tired justlike the body, it rests like the body, it loses its control over thebody just as the body loses its control over the soul…. Is thesoul gay, sad, angry, tender, shy, lustful? It is nothing without thebody. (EP; DPV XVII: 334)

He also presents the brain as the source of our identity, or of whatit is for me to be me, although he sometimes thinks it is the wholeorganism which composes our individuality. He recognizes the brain asa very particular kind of organ, one in need of special attention,and, rather unusually for the period, he seems to call attention toits plasticity in a discussion of memory:

The soft substance of the brain [is] a mass of sensitive and livingwax, which can take on all sorts of shapes, losing none of those itreceived, and ceaselessly receiving new ones which it retains. Thereis the book. But where is the reader? The reader is the book itself.For it is a sensing, living, speaking book, which communicates bymeans of sounds and gestures the order of its sensations. (DPV XVII:470)

Diderot had been discussing several extremely lyrical cases ofrecalling landscapes both in nature and in painting, and then almostabruptly turns to cerebral-material explanations of such phenomena.What is unusual about this in the history of philosophical and earlyneurophysiological discussions of the brain is Diderot’sstriking image of the brain as a book which reads itself, and theembodied brain-reader as self-organizing (Wolfe 2016b).

Even if Diderot’s conception of body and brain indicate that heis not treating them in terms of basic physics alone, he holds theexistence of causal relations to be fundamental; as he writes,“‘Every cause is an effect’ seems axiomatic tome” (DPV XXIV: 309). Without this foundationally construed senseof causality, Nature would constantly be taking leaps, which he thinksis a mistaken vision of things. In other words, he is committed to aform of determinism.

2.4 Determinism and change

All forms of materialism are deterministic, but in different ways.Nothing compels the materialist to accept that the body and thepassions are deterministicjust like a simple machine.Unsurprisingly, a lot depends on howcauses are understood,and how much weight they are meant to bear in both an ontology and anaccount of action (see entry oncausal determinism). Thus it is quite possible to hold, like Helvétius,d’Holbach or Hobbes, that there is a fixed, stable andpredictable relation between our sensory input, our mental life andconsequently our “temper” and our actions. “As abeing that is organized so as to think and to feel”,D’Holbach explained, “you must feel pleasure or pain; youmust love or hate in accordance with the way your organs are affectedby the causes surrounding you or within you” (D’Holbach1770/1781: I.i [1990: 18]).

But the organismic elements in Diderot’s materialism and visionof the body lead him to challenge Helvétius’ program ofreform, which asserts, on the basis of an empiricist and specificallysensationalist epistemology, that human beings really arefullymodifiable “blank slates”, modifiable in terms ofwhat we call stimuli and responses. Interestingly, it is by denyingthis “full modifiability” that Diderot can defend acertain notion of individuality. The fact that individuals differ fromeach other at the level of theirorganisation grants them adegree of self-determination. “Every day, I see men who preferto die rather than to correct themselves” (DPV XVIII: 344). Thatis, what Diderot calls “modifiability”, which might betterbe termed “corrigibility”, has limits, and these limits donot just reflect some kind of blunt innatism (whether of geneticheritage or of character), but rather a degree of individuality,including at the level of agency. Biologically, Diderot often stressedthe enormous variation of traits such as intelligence from oneindividual to another, noting that the difference between an“idiot” and a “genius” hinges on tiny shiftsin “brain fibers”. There is more difference, he insists,between one individual and another in terms of intelligence thanbetween a human being and an animal (DPV XXIV: 299). But there is nosharp divide between the biological and the personal, for Diderot.

Helvétius had described to Diderot how severely he was punishedforDe l’Esprit, with the consequence that he would“rather die than write another line again”. Diderotresponds with a long tale about two cats he saw from his window, whofell from a roof. One died from the fall, but the other got up,bruised and bloodied, and said to himself,

I would rather die than ever climb on the roof again. What am Ilooking for up there? A mouse that is not worth the tasty morsel Icould get from my mistress, or steal from the cook …

However, as soon as the cat feels better, he climbs back up on theroof again (RH; DPV XXIV: 542–543). Just like the catis determined by his own constitution and drives, similarly,Helvétius has no choice but to go on writing.

Diderot’s determinism is also his way of extending coreempiricist tenets such asnihil est in intellectu quod non fueritin sensu (there is nothing in the mind that was not first in oursense), which acquires a determinist dimension: “there is onlyone operation in man, sensing. This operation is … neverfree” (OH; DPV XXIV: 300; cf.PC; DPV XX: 85)and

perception comes from sensation; from perception, we get reflection,meditation and judgment. There is nothing free in intellectualoperations, or in sensation. (EP; DPV XVII: 335)

There is also a tension in Diderot’s approach to determinismbetween his acceptance of physicalism (“there is only one kindof cause … physical causes”: to Landois, DPV IX: 258) andcausal closure (“the physical world and the moral world are oneand the same”:PC; DPV XX: 53), and his insistence thatagency, which for him covers the action of complex organisms overalland is not restricted to humans or even higher mammals, requiresanother, specific kind of causality: “I am a man, and I requirecauses proper to man” (RH; DPV XXIV: 523). Diderot isnot defending free will or an unchallenged space of agency, yet thereis a kind of residual anthropocentrism in some of his arguments,presented in the language of unified causality. As he explains:

Without regard for the sum of elements of which I am composed, I amone, and a cause only has one effect. I have always been one singlecause [une cause une], thus I have never had more than oneeffect to produce; my duration is thus nothing more than a successionof necessary effects.

Diderot is neither asserting total interconnection (as in Laplaciandeterminism) nor defending the existence of freedom to act as“indifference” or “agent causation”, but anintermediate view (once known as the Hume-Mill thesis) according towhich what it is to be “me” is to be a particular causalnexus.In that sense, I cannot “do otherwise than myself”or “be anyone other than myself” (JLF; DPV XXIII:190, 28; on Diderot on individuality and selfhood, see Thiel 2015,Wolfe 2015).

However, in good Lucretian fashion, this unified causal loop we call“ourself” or “myself” is itself subject towhat Diderot terms “vicissitude”, a term that connoteschange and flux in this context.

In one and the same man, everything is in perpetualvicissitude… It is only by means of memory that we are the sameindividual to others and to ourselves. At my age, there may not be asingle molecule in my body that I brought into the world at my birth;(DPD; DPV X: 423)

everything changes, everything passes … only the Whole remains.(RA; DPV XVII: 128)

Diderot wrote that

fruits, vegetables and animals are in perpetual vicissitude as regardstheir qualities, forms and constituents; an ancient from four thousandyears ago or better, our nephews in ten thousand years will mostlikely recognize none of the fruits we have today;

thus

we must be extremely careful in our judgments of the ancienthistorians and naturalists regarding the forms, virtues and otherqualities of beings which are in perpetual alteration.(“Acmella”,Enc. I: 460a)

The instability in this continual movement between seemingly free andwillful individuality and collective, biological/metaphysicaldeterminism also sits at the heart of the perpetual dialectic between“Moi”and “Lui” inLe Neveu deRameau.

Further, this emphasis on mutability, change and“vicissitudes” including at a specifically biologicallevel can sound evolutionary to a post-Darwinian reader, and forDiderot, “to be born, to live, to die is merely to changeforms” (RA; DPV XVII: 139), in the“ever-changing” “overall order of nature”:“Everything is inin fluxu et eterno et perpetuo etnecessario” (OH; DPV XXIV: 317). He alsoexplicitly uses the Lucretian phraseRerum novus nasciturordo. Should these passages be understood as anticipations ofevolutionary science? In fact, contrary to a widespread tendency inolder scholarship, it is mistaken to consider Diderot as either apredecessor or a speculative exponent of evolutionary doctrines. Thathe was an earnest disciple of Lucretius, fascinated with monsters andwith the transience and mutability of the physical (particularly theliving) universe overall, does not make him a “forerunner ofDarwin”.

On the biological side, his fascination with monsters also feeds intohis philosophy of nature overall. “On the entire surface of theearth”, he writes,

there is not a single man who is normally constituted or perfectlyhealthy. The human species is just a mass of more or less counterfeit,more or less sick individuals … What I say of man applies justas well to animals, plants or minerals. (EP; DPV XVII:515)

This explains why, as he had written earlier,

the dissection of a monster … is more useful to the historianof nature [i.e., the experimental life scientist or biologist inmodern parlance] than the study of one hundred individuals whoresemble each other. (“Encyclopédie”; DPV VII:242)

2.5 Diderot’s philosophical anthropology

2.5.1 Aesthetics

Diderot was a thoroughgoing naturalist and empirical scientist, butthis did not mean that he neglected the aesthetic dimension of humanknowing, or the artifice of representation itself that makes possiblelanguage, communication, and human knowledge. In hisEncyclopédie entry on cabinets of natural history andtheir philosophical implications (“Cabinets d’histoirenaturelle”), he reflects explicitly on the challenge for ourfinite intellects to seek to know infinite Nature as a whole, andrecommends the construction of artificial environments such as thesecabinets in order to study “parts of Nature”. At times,his vision of aesthetics is simply a kind of extension of hisnaturalism into other domains, arguing like Spinoza that oursubjective notions of beauty and ugliness have no place in natureproperly understood (in the article “Laideur”; alsoSalon de 1763; DPV XIII: 373–374), and argues for anaturalist poetics (“Encyclopédie”; DPV VII: 234).Yet he also held that aesthetics should not be reduced to crudelynaturalistic concepts, reflecting at length on the subjective issuesof aesthetic perception and judgment and the role of performance,including that found in visual art, literature, theater, andscientific experiments, in the production of perceived truths.

With respect to the ostensibly subjective side of human knowing, heinvested considerable energy in articulating a concept of“perception of relations” (perception desrapports) which functions both as a theory of judgment(explaining why it is that we find certain kinds of symmetry andproportion pleasing) and a theory of cognitive functioning at a morebasic level, one characterized by psychoneural relations, as it were.Countering that subjective emphasis, however, Diderot also warnedagainst the “surfeit” of organic sensitivity as a sourceof hyper-reactivity, and of sensory stimulus as a ground forperception without any internal unifying principle. These reflectionsare also found in the character Bordeu in theRêve whoserves to ground the perceptions and queries from M^lle deLespinasse regarding the ravings of the dreaming D’Alembert in aclear objective ground. Diderot describes the overly sensitive actorin theParadoxe sur le comédien as suffering from a“weakness in their constitution”, and speaks ironicallyabout the welter of emotions (“des sensibilitésdiverses”) on stage being incapable of forming a unifiedwhole.

2.5.2 Philosophy of language and representation

Unifying these two aspects was the eclectic Malebranchian emphasisupon language as the bridge between the finite and the infinite, thematerial and immaterial, the human knower and nature as a whole. Inhis aesthetics, Diderot is continually preoccupied with the power ofart to capture and represent natural experience and its limitation inthe face of the infinitude, and often unrepresentable complexity, oflife. In meta-works of what might be called his philosophy of theatersuch asDiscours de la poésie dramatique andParadoxe sur le comédien, and in his dialogue where heconversed out loud with his readers about the theatrical logicunderlying his playLe Fils naturel, Diderot also pursuedsuch themes by subjecting the “reality effect” oftheatrical art to a systematic interrogation so as to unearth therational structures of theater as a representative art form.

Diderot reflected famously and influentially on what he called the“fourth wall of the theatre”, that imaginary barrier thatseparates an audience from the three dimensions of the stage it faces.This is a barrier that for Diderot acts either as conscious divisiondividing the actors and the drama from its viewer (theatre as aconsciously artificial way of representing and knowing) or as aninvisible screen through which the two join together into the jointexperience of the theatrical moment (theater as a staged naturalism).While still important in theatre theory today—Richard Sennettinterprets Diderot as “the first great theorist of acting as asecular activity” and as the innovator who creates a theory ofdrama “divorced from ritual”—Diderot’swritings on theatre also offer yet another example of his widermetaphysical and physiological understanding of human beings and theirembodied interrelation. They also highlight the role of languagethroughout his philosophy as a tangible yet permeable and sometimesfragile tether joining humans and their knowing together.

In a manner similar to his “philosophy of theatre”,Diderot’s art criticism is also very often a study of thecontinually recurring interplay between sensible human subjectivityand the natural world through the perceived empirical reality ofnatural representation. What happens when a viewer stands in front ofa painting and experiences its imagery? In particular, what is therelationship between the reality of the viewer in the Louvre in thesalon gallery in front of the paintings on display and the reality ofthe world represented by the image? What is it that happens exactly aswe move between these two worlds and realities? And given the presenceof both a painting and its artist at the center of this exchange, whatis the role played by the painter, his material medium, his craft inmanipulating matter into representations, and the viewing subject whoboth receives this artistic work in her own senses and then recreatesit in her imagination in the making of a “naturalexperience”?

To combine all these dimensions into a coherent concept of art, asDiderot did in his art criticism, was to produce a general aestheticsexploring the capacity for human representations to render experiencetruthful and meaningful. Here, Diderot also explored the power andlimitations of such practices as a form of human experience. In thisway, the problem of viewing art and speaking about the experience ofviewing art, or the question of judging artists that stage thisexperience, is akin to the problem of viewing and speaking aboutnature itself, and of judging the nature of the presentations putbefore us. Diderot’s “promenade Vernet” in theSalon de 1767 is something of a locus classicus for theseinvestigations with its extended reflection on the presence of theviewer in front of a Vernet landscape painting and the being of thatviewer in the natural world that the painting represents as well. Hiswork in natural philosophy and the life sciences often manifests asimilar subject-object preoccupation as well, and in this respectDiderot’s aesthetics and his natural philosophy have much incommon.

The same combination is present in Diderot’s literary fiction aswell in his continual, and often critical, exploration of theempirical reality of linguistic representation, and our capacities andlimitations for experiencing and knowing the world through suchrepresentations.Jacques le fataliste, for example, is a kindof anti-novel that thwarts the arrival of naturalized realism andcredible illusion at every turn even as it narrates a bawdy andfrolicking story. Characters break with the scenes and dialogue of thestory to talk directly to the reader, and the narrator himself is aself-conscious character in the work who often finds himself in astruggle with the fictions he is supposedly controlling andrepresenting for his readers.

Le Rêve de D’Alembert is also concerned with therelation between author, textual characters, and the naturalistic andrational representation of thought in language and text, as isLeNeveu de Rameau, but while these dialogues organize the playbetween their various registers in a way that produces constructivephilosophical investigation,Jacques le fataliste operatesdeconstructively, subverting the basic coherence of the novel as aform by repeating paragraphs verbatim on multiple pages and byintentionally distorting the book’s narrative coherence andflow. One entire page of the book is printed in complete black, forexample, to call attention to the print characters that make allreading and linguistic communication possible. Diderot’s storyCeci n’est pas un conte also operates in thissubversive and deconstructive way by prefiguring Magritte’sfamous conundrum regarding the image of a pipe through aself-destructive recursion of a story that uses storytelling to denythe possibility of storytelling even as it narrates a story.

2.5.3 Ethics

One striking feature of Diderot’s moral thought is hisself-described failure to write a work of moral philosophy. WhileDiderot wanted to write such a work in order to refute La Mettrianimmoralism, especially its particularly bracing form of hedonismcoupled with its cynical social theory, he ultimately did not succeedin this ambition. He interestingly described his failure, or ratherreluctance, to write a work of ethics as stemming from his recognitionthat,

if I do not emerge victorious from this attempt, I shall become theapologist of wickedness, I will have betrayed the cause of virtue, andencouraged man towards vice. (RH: DPV XXIV: 589)

Diderot had no desire to use his writings to ensure “theimmortality of the evildoer” (ibid.;ERCN II,6; DPV XXV: 246–247), and at the same time he also considerednormative moral philosophy to be a failure, a view he shared with suchvirtuous individuals as Locke. (In response to his friend LadyPeterborough’s request for advice on how to morally educate herson, Lord Morduant, Locke recommended, in a 1697 letter, that heshould read Livy (for history), along with geography and the study ofmorality. But, he explained, “I mean not the ethics of theschools”, but rather Tully (i.e., Cicero), Pufendorf,Aristotle and “above all the New Testament”, wherein“a man may learn how to live which is the business of ethics,and not how to define and distinguish and dispute about the names ofvirtue and vice” (King 1829: 5–6). This is not a ringingendorsement of academic moral philosophy, and Locke reiterates thisview in hisThoughts Concerning Education, § 185 and theReasonableness of Christianity, §§241–242.)

Another crucial feature of Diderot’s ethics was his dislike forrelativism or at least for some of its possible consequences. Diderotlearned a great deal from Locke, Montaigne and other paragons of earlyWestern cultural relativism. Montaigne and Locke paid close attentionto the case of cannibals; Locke, when he takes up the case ofcannibals in theEssay, uses it to support anti-innatistviews with respect to what he calls “practical principles”(that is, moral principles of conduct): he points out that theTupinamba tribe in the Amazon considers that a high form of virtue iseating one’s enemies, along with many other examples of“enormities practised without remorse”, in orderto stress that “moral rules” are not innate but culturallyspecific and learned (Locke 1690 [1975: I.iii.9]). The challenge isnot to morals per se but to “mores” and customs which wetake to encapsulate morality. Diderot echoes these ideas notably inhisSupplément au voyage de Bougainville, but contraryto widespread views, he did not think that such relativism had toentail libertinage, criticizing Hemsterhuis for reasoning “as iflibertinage was a necessary consequence of materialism, which seems tome to match neither reason nor experience” (OH; DPVXXIV: 251). Unlike La Mettrie (and the Marquis de Sade after him),Diderot maintained a strongly social concept of self. “He whohas studied himself”, he wrote, “will have advanced in theknowledge of others, given, I think, that there is no virtue which isforeign to the wicked, nor vice foreign to the good”(ERCN; DPV XXV: 226).While he did not develop a full-fledgedtheory of sympathy like Hume or Smith, Diderot was neverthelessacutely conscious of the role of the passions in cementing the socialbond, and how this role should be promoted in any viable ethicaltheory.

Nevertheless, his hostility to immoralist versions of materialism didnot mean that he reneged on his overall naturalism, since his accountof our behavior, and of good and evil, also seeks to tie it to ourphysiological constitution (ourorganisation, in histerms).

Ethics is confined to the borders of a species … What is aspecies? A mass of individuals sharing a similar constitution. What,is this constitution the basis of ethics?… I believe so.(SA; DPV XVI: 206)

It is perhaps too naturalistic an ethics for some since “thereis no rational goodness or wickedness, although there may be animalgoodness or wickedness” (“Droit naturel”,Enc. V: 155b). By this Diderot means that we do not act inaccordance with purely transcendent or immaterial principles in mind,but that we are determined by motives, affects, desires, instincts andso on. Yet at the same time, as we also saw regarding determinism,Diderot is concerned not only with the universe in its entirety butwith specifically human chains of causal influence as well.“What is a human being?” he asks. “An animal?Undoubtedly, but dogs are animals too; so are wolves. Yet humans areneither wolves nor dogs” (SA; DPV XVI: 205).

Diderot explicitly eschews the natural ties that many see tying amaterialist conception of human being directly and naturally withlibertinism, hedonism, and a purely self-interested and solipsisticconception of morality. This stance was reinforced in other ways byhis counter-conception of natural morality, an ethics which he oftencelebrated in his writings about aesthetic representation and itsvalue. At the center of the naturalism that Diderot claimed for thisethics was an implicit set of claims about experience, feeling, andaction in human life. The natural principles of sensibility spokedirectly to humans about the division between virtue and vice, or soDiderot believed, and while the virtuous individual was the one whosubmitted to the natural passions inherent in us pushing us towardcamaraderie and filial love, the vicious soul was a willful andarrogant rebel who chases selfish desire and self-gratificationagainst the grain of what is naturally good and true.

This metaphysical and physiological understanding of morality wascentral to Diderot’s politics as well, and with respect totheater it led him to theorize the mechanisms by which humanperformance and theatrical display both supported and corrupted thepursuit of virtue. Rousseau, with similar ethical orientations,condemned theater outright as a false and corrupting medium, arguingthat natural religion and virtue could only be practiced in a natural,i.e., non-artificial or non-theatrical way. Diderot’s view wasmuch more complicated. While he recognized the corrupting power ofartistic representation to deceive, he also recognized its power toprovoke and sustain natural experiences that promoted moral virtue.His impassioned speeches written for imagined Africans oppressed byEuropean slavery, which he included in his contributions toRaynal’sHistoire des deux Indes, illustrate well thefusion of theater and politics characteristic of Diderot. In thesemoments, Diderot used the full power of theatrical language andartificial representation to present an unequivocal statement aboutmoral and political righteousness, one designed to move people toprogressive and virtuous political action. Rousseau’s prizeessay discourses produced in the 1750s were also influential uponDiderot in shaping his views, for like Rousseau Diderot developed anideal of natural, egalitarian, communitarian virtue, which he foundmost fully developed in simple, rustic people who lived modestly andin close relation to their natural surroundings. Diderot alsodeveloped a countervailing conception of vice that was directlyconnected to wealth, especially wealth attached to elite privilege,and a morality that encouraged people to embrace basic organicfoundations for life and to turn away from urban lives of selfishnessand hedonism. The same morality infused his political economicwritings as well, both in his celebration of the communitarian powerof commerce to unite people into virtuous and prosperous polities, andin his critique of greed and commercial excess as a cause for socialviolence and political injustice.

2.5.4 “Man and world”

At the level of aesthetics, ethics or ontology itself, Diderot is amaterialist concerned with utility, praxis, transformation and yes,agency (up to a point). Some commentators in earlier generationsthought this spelled contradiction and the lack of any cogentphilosophical position. More recently, it has been recognized thatDiderot was precisely reflectingon this tension between thecosmos and time-scales stretching millions of years, and his love forSophie Volland, or his desire to see goodness rewarded and wickednesspunished. Indeed, he sometimes offers at least partial solutions tothis old aporia. If it is true, on the one hand, that

The universe only presents to us particular beings, infinite innumber, with hardly any fixed or determinate division. None can betermed the first or the last; everything is linked therein, andfollows what came before by imperceptible nuances. In this immenseuniformity of objects, if some appear which, like the tips of rocks,seem to pierce through the surface and dominate it, they only owe thisprerogative to particular systems, vague conventions, and foreignevents, not to the physical arrangement of beings and the intention ofNature (“Encyclopédie”,Enc. V: 641b)

so that there is no place for the human observer in this desolatelandscape, it is also true, on the other hand, that the only thingthat makes the existence of the spectacle of Nature interesting is thehuman presence itself:

One consideration above all must not be lost sight of, and that isthat if man or the thinking, contemplating being is banished from thesurface of the earth, this moving and sublime spectacle of naturebecomes nothing but a sad and mute scene…. Everything changesinto a vast solitude where unobserved phenomena occur in a manner darkand mute. (Enc. V: 641c)

Instead of losing himself in reveries about the poetics of ruins andour transitory existence on the face of the earth, however, Diderotinstantly asserts the pragmatic, “constructivist” andartificialist conclusion: since “It is the presence of man thatmakes the existence of beings interesting”, “Why not makeman the center of our work?” The anthropocentrism here is ofcourse not one which appeals to a human essence, or special dignityincluding some purported superiority we might possess over animals. Itis rather a pragmatic position according to which schemes like theEncyclopédie, but also the arts, sciences andtechnological pursuits narrated in that work, serve to make that“landscape” meaningful.

3. Conclusion

For Diderot, there is only one substance and it is material. Here, heis loosely aligned with Spinoza. But this substance is in perpetualflux (a more Lucretian element in his thought), so that the individualbeings we encounter are merely temporary, provisional clusters ofmolecules in interaction with one another, in the midst of what heterms the general “vicissitude” of the cosmos (by which hemeans its change). In the entry “Immuable”(“Immutable”) he writes that “Nature is in a stateof perpetual vicissitude. It follows from the general law of allbodies: either they are in motion, or they tend to be in motion”(Enc. VIII: 577).

Borrowing a Heraclitean motif and adding a now rather dated genderinflection, Diderot also describes Nature as a woman who enjoysdisguises (IN, § XII, doubtless alluding toHeraclitus’phusis kruptesthai philei, “Naturelikes to hide”, frag. 208). This is also why there are nomonsters in any real sense:

I speak of monstrosity relative to what they are at present, for thereare no monsters relative to the whole …. If everything isin fluxu, which we can hardly doubt, all beings aremonstrous, that is, more or less incompatible with their correspondingorder. (OH; DPV XXIV: 317, 403)

The matter of which we, as well as all other entities in the universe,are composed, is heterogeneous: differing in terms of energy andsensitivity, and in perpetually evolving relation to the Whole:

The world is ceaselessly beginning and ending; it is at every momentat the beginning and at the end; it never had, and never will have anyother. In this vast ocean of matter, not one molecule resemblesanother, not one molecule is self-identical for one moment.(RA; DPV XVII: 128)

That is, Nature is both fundamentally heterogeneous (the atoms whichcompose the natural world exist in a state of heterogeneity andagitation) and never entirely “specific”:

each thing is more or less specific (quelconque), more orless earth, more or less water, more or less air, more or less fire;more or less belonging to one kingdom or another … hence thereis no essence of a particular being. (RA; DPV XVII: 138)

All beings

have an infinite number of relations to one another, according to thequalities they have in common; … it is a certain assemblage ofqualities which characterizes them and distinguishes them(BI; DPV III: 183)

In this ever-changing Whole, there are provisional constructs andentities that are, like everything else, wholly material, but can beof greater or lesser significance to us, whether this is “cashedout” aesthetically, emotionally, ethico-politically or even interms of nerve impulses (and Diderot, most of the time, is not wont todistinguish sharply between these).

Diderot invented a new form of materialism, drawing on a variety ofsources including the Epicurean tradition, Hobbes and Locke, Spinozaand Leibniz. He also transformed doctrines, genres and nascentintellectual constellations (skepticism, the philosophical novel, andeclecticism, to name some instances). Even if he did not wish tocontribute to the genre of systematic philosophy, his contribution tothe Enlightenment (and its posterity) and to subsequent intellectualepisodes is considerable, difficult to measure, and should be engagedwith.

Bibliography

Primary Sources

Diderot’s Works

• [DPV]Œuvres complètes, Herbert Dieckmann,Jacques Proust, and Jean Varloot (eds.), 33 volumes planned, 25 done;Paris: Hermann, 1975–.
• Correspondance, G. Roth (ed.), 9 vols. Paris:Éditions de Minuit, 1955–1970.
• [Enc.]Encyclopédie des arts et desmétiers, 35 vols., with J. D’Alembert (eds.), Paris:Briasson, 1751–1780. Reprint, Stuttgart/Bad Cannstatt: Frommann,1966. Different online versions exist, fromLexilogos to the more officialARTFL project and the newENCRRE project.

Chronology of Writings

• 1744, translation of Temple Stanyan,Histoire deGrèce
• 1744–1748, translation of Robert James,Dictionnaireuniversel de médecine (in 6 volumes)
• 1745, translation and commentary on Shaftesbury,Essai sur lemérite et la vertu
• 1746,Pensées philosophiques (Additionswritten 1762, published 1770)
• 1747,Promenade du sceptique
• 1748,Mémoires de mathématiques (includingon acoustics)
• [BI] –––,Les Bijouxindiscrets
• 1749,Lettre sur les aveugles
• [LSM] 1750,Lettre sur les sourds et les muets(revised and published 1751)
• –––, “Prospectus” of theEncyclopédie
• 1751,Encyclopédie begins to appear (35 vols.,1751–1780)
• –––, article “Âme” (additionsby Diderot)
• 1752,Suite de l’Apologie de l’Abbé dePrades
• [IN] 1753,Pensées surl’interprétation de la nature /Del’interprétation de la nature; new edition in1754
• 1755, articles “Droit naturel”,“Encyclopédie”, “Epicurisme”
• 1756, Letter to Landois (on determinism)
• 1757(–1760),Cours de chimie de Mr Rouelle(Diderot’s notes from the three years he attendedRouelle’s chemistry lectures at the Jardin du Roi)
• 1758,Sur “De l’Esprit”d’Helvétius
• [DPD] –––,Discours de lapoésie dramatique
• 1759, Letter to Sophie Volland (on materialism, generation andlove)
• 1760,La Religieuse
• 1761, first draft of theNeveu de Rameau
• 1762, “Lui et Moi” (short story, embryo ofNeveude Rameau)
• 1763,Salon de 1763
• [EP] 1765?, Diderot begins theEléments dephysiologie (apparently unfinished, revised as late as 1780)
• 1765, articles including “Hobbisme”,“Leibnizianisme”, “Locke” and“Spinosiste” in the volumes of theEncyclopédie that appeared all together in thisyear
• 1766, Diderot begins work on theHistoire des deux Indes(pub. 1770)
• –––,Essais sur la peinture
• 1767, second draft of theNeveu de Rameau
• [SA] –––,Salon de 1767(including the “promenade Vernet”)
• 1768, probable collaboration on a translation of Lucretius’De rerum natura (by Lagrange, which Diderot laterdisavowed)
• [RA] 1769,Le Rêve deD’Alembert
• [PC] –––,Paradoxe sur lecomédien
• [PPMM] 1770,Principes philosophiques sur lamatière et le mouvement; Additions aux Penséesphilosophiques
• –––, Diderot/Raynal,Histoire philosophiqueet politique des Deux Indes
• [JLF] 1771, Diderot begins to writeJacques lefataliste (–1778)
• 1772, two editions of Diderot’s works appear in Amsterdam(one containing Morelly’sCode de la Nature)
• 1773–1774,Neveu de Rameau (final version)
• [RH] –––,Réfutationd’Helvétius (revised 1774, 1775)
• [OH] –––,Observations surHemsterhuis
• –––,Mémoires pour CatherineII
• 1774,Dialogues &Fragments (between theRêve and theÉléments dephysiologie: see DPV XVII)
• [ERCN] 1778,Essai sur les règnes de Claude etde Néron (revised 1782)
• 1784, Naigeon,Mémoires sur la vie et les ouvrages deDiderot (1784–1795)

Other Primary Sources

• Barbier, Edmond Jean François, 1857,Chronique de larégence et du règne de Louis XV (1718–1763), ouJournal de Barbier, 8 volumes, Paris: Charpentier, 1857.
• Buffon, Georges-Louis Leclerc, Comte de, 1749–1788,Histoire naturelle, générale etparticulière, 36 vols. Paris: Imprimerie Royale.
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• Goethe, Johan Wolfgang von, 1799,Diderots Versuch überdie Mahlerei, inSämtliche Werke, vol. 10,Kunstschriften II, hrsg. von M. Hecker, Leipzig: Insel-Verlag,1925.
• Helvétius, Claude-Arien, 1758 [1988],Del’Esprit, Jacques Moutaux (ed.), (Corpus des Œuvresde philosophie en langue française), Paris: Fayard, 1988.
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• –––, 1774,Le bon sens, ou Idéesnaturelles opposées aux idées surnaturelles,London: n.p.d’Holbach 1774 available online
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• King, Peter, Lord, 1829,The life of John Locke, with extractsfrom his correspondence, journals, and common-place books,London: H. Colburn. [King 1829 available online]
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• Locke, John, 1690 [1975],An Essay Concerning HumanUnderstanding, P.H. Nidditch (ed.), Oxford: Clarendon Press,1975.
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Biographies and bibliographical studies of Diderot

• Adams, David, 2000,Bibliographie des œuvres deDiderot, Ferney-Voltaire: Centre internationald’Études du XVIIIe siècle.
• Korolev, Serguei V., 2014,La Bibliothèque de Diderot,vers une reconstitution, Ferney-Voltaire: Centre internationald’Études du XVIIIe siècle.
• Spear, Frederick A., 1980–1988,Bibliographie deDiderot, 2 vols. Geneva: Droz.
• Stenger, Gerhardt, 2013,Diderot. Le combattant de laliberté, Paris: Perrin.
• Trousson, Raymond, 2007,Diderot, (Folio Biographies),Paris: Gallimard.
• Venturi, Franco, 1939,Giovinezza di Diderot, 1713-1753,unpublished in the original Italian until 1988, Palermo: Sellerio.Translated 1939 to French asLa jeunesse de Diderot (de 1713à 1753), Juliette Bertrand (trans.), Paris: Skira;reprint, Geneva: Slatkine, 1976.
• Wilson, Arthur M., 1972,Diderot, two volumes, New York:Oxford University Press.
• The journalRecherches sur Diderot et l’Encyclopédie is dedicated to Diderot and theEncyclopédie, as itsname indicates.

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Other Internet Resources

• Diderot bibliography online
• Selected Online translations:
  • Selected Writings
  • Rameau's Nephew, translation ofLe Neveu de Rameau, by Ian C. Johnston.
• ARTFLEncyclopédie
  • Droit naturel.
  • Éclectisme.
• ENCRRE project (new electronic edition of theEncyclopédie)
• La pensée des lumières: Enlightenment thinking,. an experimental digital text portal designed to help students findand use the primary texts written and published in the FrenchEnlightenment
• The University of Michigan’scollaborative translation of theEncyclopédie project
• Curran, Andrew, 2013, “Diderot, An American Exemplar?”,New York Times
• Wolfe, Charles T., 2013, “Denis Diderot and science: Enlightenment to modernity”, inThe Conversation.

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Acknowledgments

The authors wish to thank Daniel Brewer, Andrew Curran, Kate Tunstall,and John Zammito for their helpful comments and criticisms.