Denis Diderot

The Encyclopédie was, at its core, an Ne project: the conviction that the full range of human knowledge could be mapped in a single structure, that connections existed between apparently unrelated fields, and that exposing those connections would itself be transformative. Diderot's famous system of cross-references—entries that pointed readers from theology to philosophy to natural science and back again, often with subversive intent—was Ne thinking made institutional. He was not cataloguing knowledge; he was showing how ideas relate, undermine, and illuminate one another. The article on “Encyclopaedia” itself is a manifesto of connected thinking, a demonstration that the project's form was its argument.

His literary work displays the same quality. Rameau's Nephew, written over decades and never published in his lifetime, is a dialogue between a rational philosopher (clearly Diderot's own voice) and the brilliant, amoral nephew of the composer Jean-Philippe Rameau—a figure whose social parasitism and sharp intelligence make him a more compelling interlocutor than the philosopher himself. The text has no resolution; it holds its contradictions open. Ne does not always need to resolve; it finds it more interesting to map the territory of a problem than to settle it. Diderot was drawn to ideas that resisted closure—free will and determinism in Jacques the Fatalist, the relationship between mind and matter in D'Alembert's Dream—because their irresolvability was where the interesting thinking lived.

The breadth of his curiosity was not dilettantism but a structural feature of his cognition. He wrote on mathematics, on the theory of color, on the sensory experience of blindness and deafness, on the craft of sculpture, on the acting technique of stage performers. His Letter on the Blind (1749), which speculated about whether morality could exist without vision, got him imprisoned at Vincennes for four months—the authorities recognized, correctly, that its materialism was a theological provocation wrapped in a philosophical puzzle. Diderot kept producing these puzzles because Ne cannot stop finding them. The world, for the dominant intuitive, is an inexhaustible source of conceptual apertures.

What distinguished Diderot from the other great ENPs of his circle was the depth of his auxiliary Fi—a personal moral seriousness that made his intellectual commitments feel like ethical obligations rather than intellectual positions. He did not oppose slavery because it was philosophically inconsistent with natural law; he opposed it because it was wrong, viscerally and personally wrong, and he said so in terms that were unusual for their emotional directness. His contributions to the abbe Raynal's Histoire des deux Indes (1780) contain some of the most passionate anti-colonial writing of the eighteenth century, and they read differently from Voltaire's cooler polemics: they read like a man who has been personally offended by what human beings do to one another.

The letters to Sophie Volland are the purest window into this Fi. Diderot wrote to her thousands of times over nearly thirty years, and the letters are remarkable not for their philosophical content but for their emotional texture: the minute registrations of mood, the way a dinner party or a walk in the country or a piece of music could open him entirely to feeling and pour into the next letter. He described his states of mind with an accuracy and an absence of self-protection that is almost alarming. Fi does not perform feeling; it inhabits it, and reports from inside. These letters feel inhabited. He was not writing for posterity—they were unpublished in his lifetime—but for the person who mattered most to him, and that made them honest in a way that published Enlightenment prose rarely was.

His relationship with his daughter Marie-Angélique shows the same Fi at work in a domestic register. He supervised her education personally, choosing her teachers, shaping her intellectual formation with the same care he brought to the Encyclopédie—perhaps more, because this was not a project but a person he loved. The artisans and craftsmen who contributed their technical knowledge to the Encyclopédie—the glassmakers and weavers and locksmiths whose expertise Diderot documented with meticulous respect—were not abstractions to him. He believed their knowledge was as philosophically significant as the knowledge of scholars, and that belief was not merely theoretical. Fi makes the moral case personal before it makes it general.

Tertiary Te in an ENFP is a late-developing but potentially formidable capacity for external organization—the ability to build structures, manage resources, and coordinate people when the vision and the values demand it. Nothing in Diderot's biography demanded it more urgently than the Encyclopédie. The project required coordinating over 150 contributors—scientists, philosophers, craftsmen, physicians, economists—across more than twenty years, negotiating with publishers, managing censors, replacing collaborators who dropped out (d'Alembert resigned from the co-editorship in 1758 after the first serious wave of persecution), and continuing to produce his own enormous volume of contributions while holding the entire enterprise together. This was not work a purely intuitive and feeling type could do without significant organizational capacity.

What saved the project, more than once, was Diderot's willingness to make unsentimental decisions. When the publisher Le Breton secretly censored passages from the final volumes to protect himself from the authorities—removing the most dangerous philosophical content after Diderot had already corrected the proofs—Diderot's response was one of the most anguished passages he ever wrote. But he did not collapse; he completed the project. Tertiary Te operates in service of dominant Ne and auxiliary Fi: it gets the work done. It does not lead—Diderot was not a natural executive—but when the vision and the values are clear enough, it can sustain an extraordinary organizational effort over time.

His relationship with Friedrich Melchior Grimm illustrates this dynamic from the other side. Grimm was the ENTJ of their circle—the natural organizer, the networker, the man who ran the Correspondance littérairewith Swiss-clockwork efficiency and managed Catherine's cultural commissions with the precision of a diplomat. Diderot contributed to Grimm's newsletter for years, producing his art criticism—the Salons—on demand, on schedule, to Grimm's specifications. This was Te in service of someone else's structure, which suited Diderot well: he needed the constraint of a deadline and an audience to bring his diffuse intuitions into a publishable form.

Diderot left Langres for Paris in 1728 and never returned to live there. Yet Langres never quite left him. His father, the cutler Didier Diderot, appears throughout his correspondence as a figure of moral seriousness—a craftsman whose practical expertise and honest labor represented a kind of value that the salons and the academies could not match. The Encyclopédie's famous plates depicting the tools and techniques of artisan trades were, in part, a tribute to this paternal world: a philosophe's acknowledgment that real knowledge lives in the hands as much as in the head. Inferior Si works this way: it anchors the dominant intuitive in memory and origin, surfacing as a pull toward what was there before the ideas began.

His Catholic upbringing was a similar case. Diderot broke with the Church early and completely, becoming a committed materialist who denied the immortality of the soul and the existence of a providential God. But the moral seriousness of his Jesuit education never left him; it simply migrated from theological to humanist grounds. He cared about virtue, about human dignity, about the obligation of the educated to improve the condition of the ignorant, in terms that his confessor might have recognized even if the theology was gone. The inferior function carries the past forward in transformed shapes; you can take the man out of the Church, but you cannot always take the Church's moral architecture out of the man.

His trip to St. Petersburg in 1773–74 to visit Catherine II showed inferior Si operating under stress. Diderot had spent his whole adult life in Paris, and the journey east at the age of sixty was physically and emotionally exhausting. His daily conversations with Catherine—hours of argument about philosophy, governance, and social reform—were exhilarating, but the court environment was alien in ways that unsettled him. He returned to Paris tired, ill, and grateful to be home in a way that surprised him. The ENFP who has spent a lifetime in motion discovers, eventually, that the inferior function was right: the particular place, the particular people, the particular life actually matter in ways that the grand project had too easily elided.

Why ENFP Over ENTP

The comparison with Voltaire is instructive, since they are the two great encyclopedic intellects of the French Enlightenment and are often grouped together. But their psychological profiles diverge precisely where ENFP and ENTP diverge. Voltaire was a performer who needed an audience; Diderot was most himself in the letters to Sophie, alone with his thinking, writing without a mask. Voltaire managed his celebrity with strategic intelligence; Diderot never quite understood the political dimensions of his own reputation and was repeatedly surprised when his candor got him into trouble. Voltaire knew when to fight and when to retreat to Ferney; Diderot kept arguing when argument was no longer useful, because he could not separate the intellectual case from the moral one. The ENTP knows when to disengage. The ENFP's Fi makes disengagement feel like betrayal. Diderot rarely disengaged. It cost him, and he did it anyway, and the Encyclopédie exists because of it.