d'Alembert's dream

Terry Winters, Parallel rendering 2, 1997


Introduction to Denis Diderot's newly edited book

Diderot's biological materialism

“The study of medicine and physiology is to metaphysics what geometry is to logic. There is no good metaphysics without an extensive knowledge of the first two sciences and their different branches; there is no good logic without the direct application of the method and principles of geometry” (Jacques-André Naigeon, Memoir on the life and work of Diderot.


What is Diderot's place in the history of biological thought? When the philosopher died, in 1784, the scientific and academic discipline we call “biology” did not exist. In the space that would later be occupied by it, we find a plethora of knowledge, gathered under the nickname of natural history, and which, at this point in the century, were committed to investigating living beings using the methods and principles of the natural philosophy of Newton.

It was possible to be a Newtonian in different ways, but almost everyone who shared this creed – among them important philosophers such as the Marquise de Châtelet – tended to agree that the great contribution of the English geometer to philosophy is the inductive method. This consists of arriving at general laws from the analysis of particular cases, carried out by observation and confirmed by experimentation.

The seventeenth century was that of the great systems, which proclaimed the deduction of the laws of the world from universal and necessary principles found in reason and expressed in the language of mathematics (analytical geometry, algebraic calculus). The systems created in the XNUMXth century, starting with that of Newton himself, exposed with impeccable elegance in the last book of Mathematical principles of natural philosophy (1679), have another shape. The universal gives way to the general, and method replaces mathesis –in each science, generalization must respect the constitutive particularities of the class of objects it deals with.

Natural history is not much like what we understand today as science, more like an art – in which the best results are produced by the most talented men (in the period that interests us, there are no outstanding women naturalists). The analysis of physiological phenomena does not always corroborate the generalizations previously established by naturalists, introducing exceptions that often lead to the revision of theses until recently taken for granted.

As a domain of provisional truth, natural history accumulated, between 1749, with Buffon, and 1859, with Darwin, increasingly rich and precious knowledge, which, however, seems to resist definitive systematization. Not by chance, the synthesis of Origin of species it is the product of a stroke of genius – the application, without further ado, of the political-economic model of scarcity to the realm of nature, by definition foreign to political economy – and completely dispenses with knowledge of the most important thing, the laws of transmission of characters acquired in the body. course of the process of natural selection.

Diderot would not be surprised by such an unusual event in the history of the knowledge of life. In 1753 he published a pamphlet entitled Thoughts on the interpretation of nature, in which he argues that, while geometry and algebra are sciences cultivated by talented and studious men, natural history is a province of genius, who guesses the truth of nature behind the “veil” with which it insists on evading the observer unsuspecting. Without a doubt, he was thinking of the countless findings in Aristotle's biological treatises, that monument that is still unrivaled today, if we think that it was built on the foundations of a physics that almost seems to us from another world.

But I was also thinking of Maupertuis, who in physical venus (1753) outlines a theory of generation and reproduction based on a purely formal scheme of maintenance of specific characters in successive generations of individuals, and in Buffon, who, rejecting the route of taxonomic classification, proposed by Linnaeus, which leads from sex from plants to the existence of God, he emphasized the disproportion between human understanding, with its desire for stability, and the constant flux of a nature that seems to know no limits. Literally lost in the world, man puts himself at its center for methodological convenience, which allows him to institute an order, a hierarchy, and, therefore, an intelligibility that depends solely on this fiction that there would be a center, which would be occupied by his species.

This somewhat desperate resource, and, let's face it, quite precarious, is the necessary consequence of abandoning the postulate of human centrality guaranteed by the Old testment and by countless other mythologies, including those not of Semitic extraction. Discreetly, from 1753-54, natural history becomes an atheistic discipline, which dispenses with the idea of ​​a deity and often even contests it. For Diderot, all that is necessary for the knowledge of living beings is the idea of ​​a general archetype of organic forms, from which derive, by random but constant combination, prototypes of species and, from these, individuals.

Adopted by anatomists, this methodological resource replaces the metaphysics of creation. It is true that a tension remains. Buffon finds himself obliged, on the recommendation of censorious friends, to temper his atheism and to mention, whenever appropriate, a God, it is true, a very small one, in the pages of your natural history. Darwin himself becomes entangled in this web, declaring the existence of a creator who seems to have a peculiar taste for complicated and imperfect solutions, in view of the highly unsatisfactory results of natural selection - when compared, for example, to the mathematical perfection of the laws of physics .

Once again, Diderot realized the most important thing when he declared, in a letter to Voltaire dated 1758, that the empire of geometry is in the process of being contested by naturalists – who dismiss the use of mathematics as the ultimate sieve of what is or is not science. . The audacity and insolence of this diagnosis can be explained, at least in part, by the insight that belief in geometric truths, supported by reason in its healthiest use, is the last home of theology. How could there be perfect order without perfect intelligence?

It is only in the XNUMXst century that the heralds of mathematization begin to realize this problem, even striving to give the theory of evolution a mathematical guise that does not compromise it with a disguised theology. Note the following: to speak of a “blind watchmaker” is to insist on the idea of ​​the craftsman, albeit in a negative way, favoring vision. But just read the Letter about the blind for the use of those who see to realize, in the footsteps of Diderot, that vision is precisely the meaning of metaphysical illusion, blindness being a privilege that leads to the knowledge of the inexistence of an artificer. Order without meaning, regularity without necessity, system without perfection: such are the metaphysical nonsense that natural history imposes on the eighteenth century, and which continue to challenge our common sense (scientific and philosophical, including).


The three writings gathered here expose the core of Diderot's biological thinking. It would be a mistake to seek in its pages an advance in relation to current theories at the time or, worse, the prefiguration of what, seen retrospectively, was to come (but might not have). To benefit from reading it, one has to put aside for the moment what we know or think we know about the development of biology as a science. Diderot's philosophical thought developed from its own logic and has an internal reflective dynamic, which the author makes a point of making very clear in each of the plays he wrote.

The Principles, the Dream and os Elements belong to a period, beginning in 1768, in which Diderot, freed from the obligations that had bound him for twenty years to publishing the Encyclopedia, can finally resume the project of a philosophy of nature, as outlined in the aforementioned Consecutive, from 1753. With an important difference, because now he can count on allies – the doctors and physiologists of the School of Montpellier – who base the idea that all matter is endowed with sensitivity, and, therefore, that difference between the living and the inert is one of degree and not of kind.

These physiologists, Théophile de Bordeu at the head, contribute dozens of entries from the Encyclopedia, in which the investigation of vital phenomena is carried out in accordance with the Newtonian precept, with priority given to observation: what the physician sees and feels in his patient forces him to think of general laws for apparently disconnected phenomena, obtaining a coherent representation of the being alive, or of the organism.

This requires a grammatical revision, since, until then, the metaphor of the living being as a machine had prevailed throughout the century (let's think of the brain as a computer, processor, etc.). The origin of this figuration is Cartesian, and depends, in effect, on the metaphysical postulate, which Descartes endeavors to demonstrate, of the existence of two substances, the spiritual and unextended soul, and the body, extensive and material. They combine in the jewel of creation, man, in a way that is not found in any other living being – all the rest are automatons, or pure machines. We're simplifying a much richer story, but it's enough for what interests us here.

For, in 1768, when Diderot begins to write the three dialogues that make up the centerpiece of this volume – d'Alembert's dream –, many people have already noticed that the Cartesian theory does not resist the observation of some trivial facts, among which the presence of sensitivity, feeling and reason in animals other than humans, which strongly suggests the uselessness of the idea of ​​soul for the physiology. If it is true, as Descartes wants, that animals do not have a soul, and if, as everything indicates, they reason, it is better to infer, in the name of parsimony, that the human animal does not need a soul to reason.

This little sophistry is nowhere proposed by Diderot, not least because the first conversation between two characters – “Diderot” and “d'Alembert” – begins around a mysterious “point” of matter from which all properties of the thinking being, including that illustrious geometer who was also, for a time, co-editor of the Encyclopedia, next to Diderot. Dualism falls, and the idea of ​​the machine has to be revised. Diderot writes left and right, including in the pages translated here, that the animal is a machine, that the human body is a machine, and so on. But think of what he calls a natural machine or an organic machine: not so much a technical product manufactured by an intelligence as a system organized in such a way that each of the parts refers to the others, forming a whole, which reproduces itself and which, when to do so, it varies in appearance without, however, losing its fundamental form.

We are, someone would say, one step away from Darwin, but let's not give in to that sweet temptation. Something even tastier awaits us. Variation, as thought by Diderot, the transformation of organized matter, is a poetic idea, which he borrows from Virgil, Horace, Lucretius, but mainly from Ovid from Metamorphoses. The living being of D'Alembert's Dream it is an enchanting paradox, a spider that weaves itself, a swarm of bees, a bunch of grapes, a chrysalis that flies without direction or destination.

In constant transformation, Nature is flux, and form is illusion – the relativity of life and death, the transience of species, the absence of meaning, the force of an eternal and omnipotent sensibility, which sets and renews itself without any intention and which leaves, in the wake of this terrible process, an incomparable benefit: the pleasure that every living being has to enjoy a sensibility that each one feels as their own (their “I”, moral philosophy would say, committing an abuse – justifiable-of words).


Perhaps the most curious effect of Diderot's “biological” writings gathered here is the hallucinatory impression they provoke in the reader. Élisabeth de Fontenay coined the expression “enchanted materialism” to refer to this effect: a doctrine that does not clarify much, but, on the other hand, awakens and animates a reflection that, being so intense and pleasurable, serves as a testament to its pertinence . The hallucinatory effect is disguised, in the Elements of physiology, due to the serious air of the exhibition – which is not enough to contain the irruption, in numerous passages, of an aphoristic record that, decidedly, puts Diderot in the company of the Schlegel brothers.

No D'Alembert's Dream, the reader's head wavers from the presentation of the characters, all of them based on real figures, still alive at the time of composition: “d'Alembert” and “Diderot”, “Dr. Bordeu” already mentioned and “Julie de l'Espinasse”, a close friend of the geometer. This is not the place to dissect the structure of the action, which is evident from the first reading. But we would like to mention some elements that make it especially interesting; starting with the quarrel between Diderot, the materialist, and d'Alembert, the skeptic, passing through the agility of the exchanges between Bordeu and Julie, to the malicious suggestions that, throughout the conversations, suggest that reproduction and the jouissance connected to it they are the engine of Nature in constant and eternal movement.

Everything happens as if, in this theater of light and dark, the fabulation about order led to the celebration of libertinism – sexual, certainly, but also, and mainly, intellectual. It should not be forgotten that thought, excreted by the brain, is as physical as any other product of the physiological processes of the animal body. Deliberately unfaithful to real models, including himself, Diderot immortalizes these people by transforming them into characters that are hard to forget, and whose company we are reluctant to leave. But no problem :o, D'Alembert's Dream, written as bewildering as it is elegant, is one of those works that the reader frequents with profit, discovering something new and unexpected each time.


The writings that form this volume were published posthumously, the Basic on 1798, the Dream in 1823, physiology elements in 1875. United by a common theme, they differ considerably in form and style. You Basic they have the appearance of a small philosophical treatise; the dialogues of Dream they are structured in the manner of acts in a drama; you Elements, unfinished work, offer the philosophical propaedeutics for a new science. The grouping between them, never suggested by Diderot, was adopted by Dieckmann and Varloot in volume 17 of the Complete Works, which served as the basis for the present translations (Paris: Hermann, 1987). As expected from a writer of his stature, Diderot varies his style according to the requirements of each of these genres, masterfully dominating demonstration, conversation and dogmatics.

But this unit has something provisional, and should not close, in our eyes, the openings of these writings to others, composed in the same period, and also published posthumously. Although they do not deal directly with what we are calling the philosophy of nature, works such as Rameau's Nephew, Supplement to Bougainville's Voyage, Jacques the Fatalist and Comedian's Paradox are to some extent indispensable if we are to have a fair idea of ​​the scope in which the Dream inserts itself, bringing with it and justifying the existence of Basic and Elements – pieces that would not have the same interest without the triptych of dialogues that connect them.

In any case, we have there, in these great texts of maturity, the testimony of Diderot's stature as a philosopher and as a writer. On the signs that signpost the boulevard Diderot in Paris, he is called “philosopher”, unlike Voltaire, who, on his boulevard, is named “writer”. Anyone who has dedicated himself to the difficult task of faithfully translating it from French knows that these two occupations were, for him, as for Voltaire, too, inseparable. The translations that follow were carried out with the intention of bringing to our language, if not all, at least a good part of the lightness, agility and philosophical genius of this incomparable author.

Addressing us without intending to do so, speaking from a century onwards, from an age increasingly foreign to ours, Diderot, philosopher of nature, is the bearer of a secret that we are interested in knowing. For there to be biology, there must first be materialism – not as an alternative ontology to existing ones, but as a point of view for enunciating the “real”: for its realization in discourse.

*Pedro Paulo Pimenta He is a professor in the Department of Philosophy at USP. Author, among other books, of The fabric of nature: organism and purpose in the Age of Enlightenment (unesp).


Dennis Diderot. d'Alembert's dream and other writings. Organization: Pedro Paulo Pimenta. Translation: Maria das Graças de Souza. São Paulo, Unesp, 2023, 316 pages (https://amzn.to/3OSKaXI).

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