Pondering Diderot’s Encyclopedia Never Ceases to Blow My Mind

Encyclopedia Page, Fencing

In the fall of 2011, I signed up for a French literature course at Eastern Michigan University. I loved the class and am indebted to our professor, Benjamin Palmer, who improved my understanding of great literature and its relationship to history. I enthusiastically enrolled in a second semester that winter and again enjoyed every minute. Throughout that academic year, however, nothing impacted me more than my firsthand encounter with an 18th-century copy of Diderot’s Encyclopédie.

The story of how Denis Diderot produced this masterwork, a 28 volume encyclopedia containing more than 76,000 entries, is mind-boggling. In 1746, he and the French mathematician, Jean-Baptiste d’Alembert, set out to create an encyclopedia that would describe and illustrate all available human knowledge. D’Alembert is often listed as a co-author but there is no doubt that without Diderot’s fanatical devotion, the project would have never come together.

In fact, there were many contributors but Diderot was chief among them, producing more than 7,000 articles. He also acted as editor, soliciting and proofreading thousands of contributions, working with engravers who created etchings of illustrated submissions, updating pages when new discoveries were made, and creating a master index of all articles and artwork. When completed, the Encyclopédie contained 17 volumes of articles and 11 volumes of illustrations.

Encyclopedia Page, Architecture
Architecture, capitals

It’s difficult to imagine the coordination and concentration needed to complete such an immense undertaking. Added to the complexity was the perpetual overhead of remaining in the good graces of a hypersensitive king and the even touchier Catholic church. Both of these powerful institutions had strong reservations about disseminating knowledge to the average citizen—Diderot’s ultimate target audience.

Indeed, Diderot was often under police surveillance and at one point he was sentenced and incarcerated in the prison of Vincennes. Many of his supporters suffered even greater persecution and frightened contributors withdrew from their prior commitments. More than a decade before the first edition was completed, both Louis XV and Pope Clement XIII banned production and financing of the exhaustive Dictionary of Reason, as the Encyclopédie’s subtitle proclaims.

Rather than fleeing the country, however, Diderot continued the dangerous enterprise from his home in Paris. With financial support from Catherine the Great of Russia and secret backing by the king’s censor (Malesherbes) and the king’s mistress (Madame de Pompadour), Diderot labored on.  When printing in France became too risky, Diderot found publishers in Switzerland. While not known for his discretion, he managed to quietly produce new volumes, sending only the engraved plates out of the country for printing while authorities turned a pre-negotiated blind eye.

Encyclopedia Page, Anatomy of the Ear
Anatomy of the Ear

I’d only learned a part of this story from Professor Palmer back in 2011 when he led our class to an archival room in the campus library. Once seated in pairs behind long tables, we obediently donned the vinyl gloves that were to stay on throughout our visit. It wasn’t long before a tired-looking gentleman wheeled in two metal carts, loaded with an entire 28-volume set for us to examine.

Looking back, I realize that I had no idea what to expect. Printed in Italy sometime in the 1770s, the ancient books were enormous. Each cart appeared to weigh more than the unassuming curator charged with loading them up. Our soft-spoken host explained that only he could remove the volumes from the carts but that he was happy to deliver any volume to our seat where we could examine them one at a time. 

My partner and I chose one of the volumes of illustrations and opened to a random page. Seeing the astonishing level of detail contained on each plate blew my mind. As we leafed through, I often felt like I wanted to linger on certain pages, partly to absorb the content and partly to marvel over what lay in front of my eyes. Knowing our time was limited, however, we were careful to maintain a pace that allowed us to peek at a few different volumes, sampling several dozen plates before our hour was up.

Encyclopedia Page, Sea travel
Sea travel

One thing I found fascinating was the depth of knowledge that had already been acquired about human anatomy. Detailed drawings of intricate portions of the circulatory system, skinless models of musculature not unlike what you’d find in a doctor’s office today, multiple views of the bones and tendons in a hand, cross-sections of the human head: these make up a tiny sampling. Even more engrossing were the sections on technology and craftsmanship: the inner workings of shipping locks; military use of trebuchets and catapults; drawings showing how to make knives, cookware, lace, furniture, paper, clocks, you name it. If it existed in late 18th-century Europe, you’ll likely find it in Diderot’s encyclopedia. There are 54 illustrations dedicated simply to the manufacture of glass.

The artistry employed to produce these frozen snapshots of human history is equally spellbinding—beauty encased in an idealized coating of precision. Yet, the illustrations account for less than half the work. The 17 volumes devoted to articles contain roughly 20 million words. It’s hard to imagine organizing that much information by hand. Now consider that each article, where appropriate, includes cross-references to pages in the related volume of illustrations.

Of particular interest for me was Diderot and d’Alembert’s Tree of Human Knowledge, which Professor Palmer had alluded to in class. This controversial 6-page foldout attempts to categorize all areas of human understanding by placing leaves of comprehension on a massive tree of knowledge. Upon first glance, the immense diagram seems like a useful way to visualize the encyclopedia’s massive and varied content. However, the Catholic Church viewed the chosen organization of subjects as an overt attempt to undermine its authority. Their assessment was not off base.

Encyclopedia Page, Tree of Knowledge
Tree of Knowledge, click on image to zoom in and scroll

Unsuspecting readers now found Religion on a sub-branch of Meta-physics which was subordinate to Philosophy rather than dominating a category of its own in which man’s ability to reason plays no role. Subjects such as Black Magic, Divination, and Cosmology descend from the same hierarchy. The relative size of each leaf also says something about its importance—theology occupying no more space than mineralogy.

Encyclopedia Page, Paper manufacturing
Paper manufacturing

With tens of thousands of articles, the Encyclopédie is hardly a revolutionary treatise against religion or even monarchies. But Diderot, d’Alembert, and other contributors lightly salted the text with mild challenges to the political and spiritual authorities of the day. Like this gem, filed under Political Authority: “No man has received from nature the right to command other men.” Or, the multi-page logistical analysis of what it would have taken to actually build Noah’s Ark. The matter was treated with all seriousness but any halfway astute reader recognizes the absurdity of such a vessel.

It’s impossible to overstate the sacrifice that Diderot made in seeing the Encylopédie through to completion. He often took on articles that no one else seemed interested in writing, spending his days mastering subject matter— often through firsthand observation—and his nights cranking out essays by candlelight. He proofread and rewrote countless articles from less competent authors and was frequently harassed by personal threats and police raids. His finances suffered as did his eyesight.

Diderot’s seemingly unflinching commitment to lift the sails of the common man stifled his ability to advance his own philosophical arguments. While Diderot did produce several over works throughout his lifetime, he never enjoyed the same level of notoriety nor the financial rewards achieved by his friends and fellow contributors Voltaire and Rouseau. Perhaps the most debilitating blow came after 20 years of toil, just as Diderot could finally see the project coming to a close. To his horror, Diderot learned that his publisher, Le Breton, had stricken passages that he deemed potentially offensive to Church and State from the final 10 volumes. Le Breton also burned the original manuscripts, rendering their reproduction impossible.

Encyclopedia Page, Mollusks

Deeply dillusioned and strapped for cash, Diderot nearly abandonned the project. Encouraged by friends and bankrolled by Catherine the Great, the crestfallen mastermind decided to move forward, now putting his energies into striking a deal with the king’s new censor to allow distribution of the the Encyclopédie in France. Another 6 years would pass before the final volumes were sent to the original subscribers.

Sadly, Diderot never recovered from Le Breton’s betrayal. He died 12 years later, believing he’d failed to leave a significant imprint on posterity but satisified that he’d at least lived an honorable life. He undoubtedly never thought that his work would one day be accessible in dozens of languages to anyone in the world with access to a global information network. But, I like to imagine that he fell asleep at night assured that certain students of French literature, living in the 21st century, might happen upon his back-breaking masterpiece and reverently stand in awe of his dedication to man’s enlightment.

“The goal of an encyclopedia is to assemble all the knowledge scattered on the surface of the earth, to demonstrate the general system to the people with whom we live, & to transmit it to the people who will come after us, so that the works of centuries past is not useless to the centuries which follow, that our descendants, by becoming more learned, may become more virtuous & happier, & that we do not die without having merited being part of the human race.”

Denis Diderot, 5 October 1713 – 31 July 1784

Other Resources

About Carol A. Seidl

Serial software entrepreneur, writer, translator, and mother of 3. Avid follower of French media, culture, history, and language. Lover of books, travel, history, art, cooking, fitness, and nature. Cultivating connections with francophiles and francophones.


  1. What a fascinating bit of history! I’d never heard of Diderot’s accomplishment!

  2. What a noble endeavor, and what an impressive result! Wish he could have known his work would still be admired more than ~225years later….

  3. Oh yes the great Denis Diderot! I have the book Supplément au Voyage de Bougainville great find. Salut

  4. Most only remember Voltaire and Rousseau. Sadly more the latter than the former.
    But. But. But… Diderot – and indeed d’Alembert were even more influential. Diderot and the even lesser remembered Montesquieu shaped the world we know today.
    (You “touched” an original? I am green with envy…)

    • Yeah, I read a biography about Rousseau shortly after taking the class which didn’t in any way endear me to the man. Diderot and Voltaire, on the other hand, are very embraceable characters. Someday, I hope to read more about d’Alembert and Montesquieu. Especially, the latter who seems to have had an incredible influence over the US constitution.

      Yes, I did get to touch those magnificent volumes. I spoke with one of the librarians while working on this piece to confirm some of the details from my memory. She said that I can make an appointment to see them again. Come to Ann Arbor, and I’ll set one up! 🙂

      • Rousseau, unfortunately, had a major influence on French “intellectuals” and educators, up till now. Montesquieu developed the concept of balance of powers… And yes the leaders of your revolution most certainly all spoke French. I Know Benjamin Franklin did…)
        Now TBH I think an Englishman explored the concept before or at the same time… Hobbes maybe… lemme check.

      • No, no… Not Hobbes. Locke. And the fathers of the Constitution certainly read Locke too AND Montesquieu. Do look both up.
        Now Ann Arbor? That would be nice. Paradoxical to see it in the US and not in France but probably easier… I’ll let you know next time I’m in Ann Arbor, and we’ll get together.

  5. PS. I don’t think we discussed it, what made you so interested in French and France?

    • Vocabulary used in my ballet classes? A few French Canadian ancestors? A mother who loved languages? Chromosomal anomaly? Qui sait?

      • French Canadians? Intéressant. What’s your maiden name? (If I may ask)
        I think your mother must have a strong influence (Beyond le pas de deux…)
        What languages did your mother speak?
        (J’adore ce genre de choses)

        • My maiden name is Neubrecht. All Dutch and German on my Dad’s side. My mother’s maiden name was Newell but that was her father’s stepfather’s name. My grandfather’s mother was a Pelletier, his biological father was Thériault. My mother studied Latin and Ancient Greek but she also took a couple classes of French and Spanish in college. She became an early elementary teacher. Then in her 50s she went back to school and became a high school French teacher. Unfortunately, our pursuits of French never overlapped.

          • Neubrecht is definitely German…
            Now Pelletier and Thériault is soooo French.
            Latin and – I imagine – Greek are great language tools. I did Latin, no Greek, and Latin has helped me enormously to learn languages. Word structure basically.
            She went back to become a French teacher in her 50’s? Mes félcitations…
            I imagine she is gone now, but I’m sure she would have liked your current pursuit… Continue la “poursuite”. (Pas exactement le même sens en Français, but I’m sure you have run into many “faux-amis”.)
            A bientôt Carole…

          • She was and I am agnostic so my belief regarding whether we’ll ever get to hold a conversation in French is faint at best. However, I do hold out a sliver of hope that given infinite time and a near infinitely large universe, our essences will reconstitute at some future (time, space) coordinate and we’ll finally share our infatuation with la langue française.

          • Agnostic now? Moi aussi. So I do have my very serious doubts about such “reunions”.
            Daughter #2 often tells me she wishes my mother, her grandmother were still around to know the new babies…
            But… I also believe those who’re gone live in our minds and memories. So you can just visualize a conversation “en Français” with your mother. Ça marche aussi.
            A bientôt mon amie.

  6. A gargantuan achievement. I had read about this before — I think you posted about it, months ago? — but I don’t recall reading about the publisher’s censorship of the passages deemed “offensive”. Has the deleted material ever been recovered? I suppose not, if they burned the manuscripts (a shocking barbarism for a publisher to commit).

    But it is a telling example of how the great men of history manage to move humanity forward, generation by generation, despite the obstacles created by the petty little kings and popes and officials scuttling around their ankles.

    I can see why the Church did not like the “tree of knowledge” foldout. Almost the whole right-hand half of it is taken up with the sciences, while I had some difficulty finding “religion” — off at the other side next to magic and divination.

    It would be interesting to read that analysis of Noah’s ark.

    • Great observations and questions Infidel. In 1933, a German bookseller put an entire set of l’Encyclopédie up for auction. Its provenance was stated as having belonged to a Tsar of Russia. Upon further examination, however, it was discovered that the set had been Le Breton’s personal copy. Along with the 28 volumes, there was an additional volume of 284 pages. Historians don’t know if they represent everything that Le Breton extracted but certainly, they fill in most of the missing text. What a treasure, heh?

      Regarding Noah’s Ark, I’ll try to dig up something to send you.

  7. This is a fine essay on Diderot’s master work. I knew a bit about it, but you’ve provided an abundance of rich detail about the effort, the content, and the environment.

    I was taken by the funding sources: Catherine the Great of Russia and the king’s censor and mistress. Surely a measure of rough justice there!

    Your description of The Tree of Human Knowledge would have been a satisfying read even without the rest of this super overview. Such a creative approach that fertile Tree demonstrates—and such courage it took for its creators to buck the orthodoxy of their time.

    Your observation about Diderot’s “unflinching commitment” in behalf of the common man and the toll it took on his own philosophical work, and your closing sentence about 21st century people gaining access to this huge effort, made me feel you served Diderot well. They also struck me as particularly lovely examples of creative nonfiction. There’s another professor who’s served you well.

  8. So glad you discovered this amazing work. I remember being blown away when I discovered it through my philosophy classes a few decades ago.
    It was nice knowing a bit more about you and your family through the comments. I liked your possible explanation “Chromosomal anomaly”, lol, rien n’est impossible

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.