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Denis Diderot: Sensibilité and Matter

Throughout his life, Denis Diderot had trouble grappling with the religious conceit that natural phenomena could be explained away by supernatural principles that couldn’t be directly observed. For him, “confirmation through the senses, whether by touch, vision or any other, [wa]s needed to sustain belief.”1 As a result, any argument for a natural order of the universe relying on God was rather unconvincing for him. With this rejection of religious explanations for the material world, Diderot set out to derive a methodology in which the universe could maintain order and natural law without depending on anything outside itself. This goal led him to construct a materialist philosophy to explain all the workings of the universe in terms of matter alone. While Diderot never formally spelled out his materialism in any of his works, its ideas came to be dominant themes throughout his oeuvre, especially in Rêve de D’Alembert (D’Alembert’s Dream), a set of three dialogues published posthumously in which characters expound upon various aspects of Diderot’s ideology.

In the first dialogue of the Rêve, the character of Diderot spells out for D’Alembert the organizing principle for all of his materialism – sensibilité. Most closely translated at sensitivity, but often used in his work to mean something closer to irritability, consciousness, or sensibility, Diderot describes this idea of sensibilité as an essential, “universal property belonging equally to every molecule of matter.”2 In this view, molecules belonging to animate entities have a sort of active sensibilité, or active consciousness, while inanimate molecules have merely a potential sensibilité latently residing within them. Any inanimate matter, Diderot believed, could become animate by being incorporated with living matter through motion and heat, commonly expressed through the process of being eaten by a living being. As the character of Diderot explains, when you eat, “you remove the obstacles that were preventing the emergence of active consciousness in the food” as you “assimilate the food and make it part of yourself,” thereby making it become animal and conscious.3 He demonstrates how this process can apply to any inanimate matter by giving an example of a marble statue as it can be ground up and incorporated with soil for vegetables to grow out of, thereby allowing it to become digestible. Conversely, animate matter can once again become inanimate with only potential consciousness through the process of death, returning their molecules back to the earth to be dispersed and absorbed into other forms. 

Following this principle, the entire universe, for Diderot, is a single substance made up of contiguous sensitive molecules. Importantly, though, the logic of such a universe, Diderot believes, hinges on the fact that there “is not a single molecule that is just like another, and in every molecule not a single atom that is just like another atom,” as such, every arrangement of atoms in the universe is a unique configuration.4 Consequently, the current state of the universe is contingent upon its particular organization at any particular instant, but, for Diderot, the universe is perpetually in a state of constant flux, continually moving and changing. Thus, the current form of anything is ephemeral as it is contingent upon the configuration of molecules which are in constant motion. This is the reason why such molecules must necessarily have the property of sensibilité, allowing any piece of matter, at any instant, to contribute to the form of an animate body. In this way, for Diderot, “the difference between a piece of marble and a sensing, conscious creature is only a difference in the temporal stages of a portion of matter in transformation.”5 Whether some bit of matter is conscious simply depends on at what point in time you observe it, for it may be part of an inanimate rock at one moment and part of a newborn chick in another. 

The consequence of such constant change, or “vicissitude” as Diderot puts it, is that all bodys in the universe are connected, and thus rely on the existence of each other as matter flows from one place to another. As the character of D’Alembert puts it in the Rêve, “Every animal is more or less human; every mineral is more or less vegetable; every plant is more or less animal . . . in nature everything is bound up with everything else, and . . . it is impossible that there should be any gap in the chain of beings.”6 The necessary repercussion of such reasoning is that the very concept of identities ceases to exist as no one thing can be so differentiated from another to warrant its own category of existence. In such a view “creatures are reduced to their lowest common denominator and identified merely in terms of the material substance of which they are uniformly made.”7 Identities and essences are then simply modes by which our minds try to distinguish things in a universe that necessarily refutes such discrimination as its flux denies the existence of any eternal forms. As a result, all that is constant is matter itself, as matter “dispersed with each death, survives to regather itself into new forms again and again through all eternity.”8  The difference between any one thing is simply reduced to a matter of organization of molecules, for all that truly distinguishes a man from an instrument is an organization of particles that warrants sensation of memory.9 

This seems to not be the conclusion Diderot had hoped to come to. His quest began simply to explicate a picture of the universe that could preserve order without the intervention of a greater power, but what he stumbled upon was a materialist system that “effectively denied any value to human life and destroyed the grounds for man’s self-assurance.”10 Man is degraded to be no more special than a pebble, which itself is raised to have a capacity for consciousness and sense perception previously thought to be unique traits of animal species. Soon after completing the Rêve, in a letter to his mistress, Diderot would come to dismiss his own system, believing that it would be “foolish and childish to deny all values in the interest of maintaining a logically consistent position.”11 Though he could not refute that his own arguments were intellectually sound, he couldn’t bear to accept their emotional consequences, to live in a world so stark and dehumanizing. As Diderot painted a picture of the universe in which man was no longer the handiwork of God and change became the only thing eternal and constant, he may have developed an adequate explanation for the questions he originally sought to answer, but such elucidation inevitably resulted in what he believed to be an emotionally unsatisfactory conclusion. 

Endnotes:
1 Emita Hill, “Materialism and Monsters in ‘Le Rêve De D’Alembert’,” Diderot Studies 10, (1968): 67-93, http://www.jstor.org/stable/40372379, 72.
2 Ibid, 76.
3 Denis Diderot, “D’Alembert’s Dream,” in Rameau’s Nephew and Other Works, trans. translated by Ralph H. Bowen and Jacques Barzun (Indianapolis: Hackett Publishing Co, Inc, 2001), 94.
4 Ibid, 104.
5 Charles T. Wolfe and J.B. Shank, “Denis Diderot,” in Stanford Encyclopedia of Philosophy (Spring 2021 Edition), ed. Edward N. Zalta, Metaphysics Research Lab, Stanford University, June 19, 2019, https://plato.stanford.edu/entries/diderot/.
6 Diderot, “D’Alembert’s Dream,” 124.
7 Hill, ““Materialism and Monsters,” 87.
8 Ibid, 85.
9 Diderot, “D’Alembert’s Dream,” 101.
10 Hill, ““Materialism and Monsters,” 71.
11 Ibid, 91.

Bibliography

Diderot, Denis. “D’Alembert’s Dream.” In Rameau’s Nephew and Other Works, translated by Ralph H. Bowen and Jacques Barzun, 89-175. Indianapolis: Hackett Publishing Co, Inc, 2001.

Hill, Emita. “Materialism and Monsters in ’Le Rêve De D’Alembert’.” Diderot Studies 10 (1968): 67-93. http://www.jstor.org/stable/40372379.

Wolfe, Charles T., and J.B. Shank. “Denis Diderot.” In Stanford Encyclopedia of Philosophy (Spring 2021 Edition). Edited by Edward N. Zalta. Metaphysics Research Lab, Stanford University, June 19, 2019. https://plato.stanford.edu/entries/diderot/.

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