Man the Machine, Dismantled

This is the second is a series on historical “meanings of life.” You can start with this one, or click here to visit the introduction first. Future installments are forthcoming.

In 1738, affluent Parisians flocked to an exhilarating new exhibit at the Hôtel de Longueville that featured a flutist, a pipe-and-tabor player, and a curious duck that would eat corn right out of your hand and defecate only moments after. The organizer of the event, Jacques de Vaucanson, acquired considerable wealth and fame in the years to follow — Frederick the Great personally invited him to join his court in Prussia, and Voltaire granted him the illustrious title of “Prometheus’s rival.”1 Of course, these were not normal musicians — in fact, they were not even very good — and this was certainly no normal duck. All three were automata: elaborate machines designed to imitate life. 

Vaucanson’s mechanical creatures needed to delight audiences with their ingenuity in order to justify the high price of admission, but they were also experiments of a philosophical kind. As Jessica Riskin observes, “their value as amusements lay principally in their dramatization of a philosophical problem that preoccupied audiences of workers, philosophers, and kings: the problem of whether human and animal functions were essentially mechanical.”2 If machines could successfully emulate musicianship and digestion, then perhaps all the mysteries of life could be reduced to levers, pistons, pulleys, gears, and rubber tubes. 

Fig. 1: An artist’s rendition of Vaucanson’s “digesting duck,” the hypothetical automaton that could fully digest grain. The original digesting duck was actually fraudulent; when fed, it would eject fake feces that had been stored up its rear.3

Vaucanson’s machines were tests of the “mechanical” philosophy, which had come to dominate intellectual thought during the “scientific revolution” of the 17th century. According to “mechanism,” there exists a set of precise and uniform mathematical laws that govern all physical things. In compliance with these laws, the world functions like a giant machine, mere matter in motion. The automaton metaphor was perfectly suited to this vision because only the laws of physics are required to describe the operation of a machine. Physicians and philosophers speculated that everything, even life itself, could be reduced to an automaton. Could one therefore “build” a human being? Some believed so; Claude-Nicolas Le Cat, head surgeon at Rouen, once hypothesized an automaton that “will develop a fever, will be bled, will be purged, and it will be all too like a man.”4

Since then, the automaton analogy has evolved to keep up with the times, as seen in the popular trope of a humanoid robot with artificial intelligence. The mechanical philosophy, attentive most of all to the laws of physics, also lives on, albeit utterly transformed by electromagnetic and quantum theory. On the other hand, the original version of “mechanism” that impelled Vaucanson to design mechanical men has long since fallen out of favor, largely driven by developments in science. In this piece, we will explore the mechanical “meaning of life” and why it was dismantled — or rather, how “man-the-machine” collapsed under its own weight. 


By all accounts, René Descartes was mechanism’s most distinguished advocate and the first to emphatically articulate its principles. Although he was not the first to compare humans to machines, Descartes inspired generations of physicians and philosophers with his mechanical descriptions of living beings:

…the body is nothing else but a statue or earthen machine, that God has willed to form entire, in order to make it as similar to us as is possible… he put in the interior all the parts which are required to make it walk, eat, respire, and that it imitate, in the end, all of our functions…

René Descartes, Treatise of Man (1633)5

The metamorphosis of man into machine illustrated a central tenet of the new philosophy: that “occult” forces and qualities had been triumphantly eliminated from the world. In the usage I refer to here, “occult” did not designate the supernatural or magical, as in the modern sense, but rather hidden, unintelligible, or unknowable things.6 Mechanistic explanations eschewed all “hidden” interferences, whether from God, spirits, harmonies, or other kinds of immaterial causes. Alongside the occult, mechanism also banished all irregularities, instead viewing the world mostly in terms of the predictable interactions between physical things, like the parts of a machine.   

If nothing is hidden, then nothing is inherently unknowable and everything in the universe is available to scientific inquiry. Emboldened by this revelation, the “mechanists” replaced obscure, occult qualities with universal, mathematical laws of nature that humans could discover. Rejecting the old Aristotelian doctrines wholesale, they embarked on a new quest to reverse-engineer the inner workings of the world, and over the course of the 17th century, their approach was validated by numerous breakthroughs. These include Kepler’s laws of planetary motion (1609-19), the Snell-Descartes law of refraction (1637), Galileo’s law of falling bodies (1638), Boyle’s law (1662), and Newton’s laws of motion (1687). 

Apart from the laws of nature, machines also require something to set them in motion. Everyone could agree that matter moves according to the laws of physics, but there wasn’t an obvious reason why anything moved at all. Put another way, the machine needed a motor to supply it with energy and get the gears turning — and this proved to be a suitable role for God and human souls to play. As I discussed previously, early modern theories of life focused on the notion of the soul, and this did not change with the emergence of mechanism. But how exactly did the soul fit into the new vision of a world reduced to matter in motion, devoid of “occult” influence? 

Descartes answered the question by separating the soul from the world of material things: the body obeys the laws of motion, but the mind obeys of the laws of reason. Splitting human existence into two independent entities, Descartes allowed mind and body to communicate only through the pineal gland in the brain. This link was necessary because the body could not move without the soul, and needed it specifically to direct conscious actions.8 This theory, known as mind-body dualism, made the human soul totally immaterial and largely disconnected it from the body in order to preserve a material world free of extraneous influences.

In the process, the “soul” lost its relevance in science and medicine, since it couldn’t be used to explain anything pertaining to material reality. As far as science was concerned, the body was just a machine that drew its power from the soul.

Since doctors have begun to examine the structure and action of the animate body on the basis of geometrical and mechanical principles… [they have] realized that as far as its natural actions are concerned the human body is nothing more than a complex system of mechanical and chemical movements that obey mathematical laws.

Giorgio Baglivi (1696)9

Even Descartes, who emphasized the significance of the rational soul, recognized that the physical body could largely function on its own. In fact, he argued that animals don’t have souls at all, indicating that most kinds of vital activities, including decision making, could be understood mechanically.10 Theories of human life still depended on the soul, but it now occupied a marginal role in the functioning of the body.

Just as the soul was the source of motion for the body, God was the source of all motion and activity in the world. Pierre Gassendi wrote that “through the force which is continually received from the Author from the beginning, [atoms] give motion to all things.” Similarly, G. W. Leibniz asserted that the forces within matter that allow it to move cannot exist independently of God.11 The universe of the mechanists was permeated by a divine spirit, without which nothing could exist. It was also important to them that the will of God be expressed in the uniform laws of nature that he created, rather than in miracles or divine interventions. In a world ruled by divinely inspired laws of motion, mechanists believed, nothing is left to chance.12 Although this view encouraged admiration for God’s creative powers and his ubiquitous influence, in practice it excluded God from scientific study. Mechanism needed a God to create the world-machine and set it in motion, but it did not need a God in order to describe the precise workings of the laws of nature. 

For a time, it seemed that mechanism might succeed in limiting scientific study to the laws of motion alone; it already threatened to eliminate the influence of spirits and God. As we will now see, however, even the powerful new science had its limitations, things it could not explain. It was only a matter of time, perhaps, before occult qualities, or something similar, returned to fill in the gaps.


Today, Descartes is most famous for declaring “I think, therefore I am” (“Je pense, donc je suis”). In other words, if there is thought, then there must be a thinker. Descartes similarly concluded that Reason and God are self-evident. He considered these three things completely inarguable, asserting that the human mind must logically recognize their existence, with or without additional supporting evidence.

The first [precept of my method] was never to accept anything as true if I did not have evident knowledge of its truth… and to include nothing more in my judgments than what presented itself to my mind so clearly and distinctly that I had no occasion to doubt it.

René Descartes, Discourse on the Method (1637)13

Descartes applied the same general method, prioritizing “clear and distinct” ideas in his mind, to his explorations of mechanistic science. Rather than basing his theories on careful observation of the world around him, Descartes would have a theory spring forth fully formed in his thoughts and then compare it to experimental data to verify whether his hypothesis was valid.14 This intuitive method enabled him to spontaneously fabricate odd theories and convince himself of their truth — he once detailed the anatomical reasons why a corpse bleeds in the presence of its murderer!15

Contrary to popular belief, however, Descartes also readily admitted that many things cannot be intuitively understood, that there are limits to what the human mind is capable of realizing on its own. Many others reached the same conclusion; Leibniz wrote that “there exists no part of nature subject to perfect understanding,” and the physician Guillaume Lamy commented “that our mind is limited, and the most learned are those who are convinced that we can know nothing.”16 Opinions varied considerably, but the vast majority of 17th century thinkers accepted that there were limits to human knowledge. 

This included even Isaac Newton, renowned for taking the mechanistic spirit of his age and refining its method, producing its most compelling results and setting the standard for scientific inquiry. Newton rejected the “hypothetical” method of Descartes, dismissing the capacity of human intuition to come up with plausible theories on its own. Instead, Newton claimed, one must look at the observational data first, and then make inferences based upon it. This is how he “discovered” the laws of motion and gravitation: through a rigorous induction from experimentation. 

But Newton also shared much of Descartes’s worldview, especially an acceptance of the limits of human reason. In the Principia Mathematica (1687), he described the law of gravitation with mathematical precision, but was unable to determine why it works:

But hitherto I have not been able to discover the cause of those properties of gravity from phænomena, and I frame no hypotheses.17

Nevertheless, Newton was satisfied with what he was able to accomplish based on the evidence he had. Instead of theorizing the cause of gravity, he declared that he “frame[s] no hypotheses” concerning things he couldn’t explain (Latin: “hypotheses non fingo”). According to his method, the bounds of science are delimited by evidence; wherever the evidence cannot go is no place for the discerning scientist. Newton’s brand of careful empiricism differentiated him from mechanists like Descartes and Leibniz, establishing a new school of “Newtonian” thought that would come to define 18th century science.

Instead of attempting in vain to explain gravity without proper evidence, Newton characteristically accepted that it had some hidden underlying cause. In this way, he reintroduced the unknowable into the fabric of the world, inserting it into the crevices that science could not reach. Gravity set a particularly powerful precedent because it suggested a latent principle of all matter that generates attractive forces from within. Newton proposed this himself, hypothesizing “a certain most subtle Spirit, which pervades and lies hid in all gross bodies [that is, material objects].”18 So much for “hypotheses non fingo.” 

Since the laws of motion had no apparent cause, 18th century Newtonians came to understand universal attraction and other forces as essential properties of matter itself.19 As a result, matter regained the power to move on its own and no longer depended on the active presence of a soul or God. This development also revived the possibility of other, yet undiscovered forces similarly hidden as a “Spirit” within matter; surely, gravity was not the only one. Thus, when Newtonians found themselves unable to explain the causes behind organic processes, they began to posit an unknown principle called “life” embedded in living creatures but not found in corpses or inanimate material.20 The source of this life principle remained as mysterious as that of gravity, but this was not a serious impediment to their project. Just as Newton had detailed the mathematical laws of motion, life scientists believed they could do the same for the uniform laws that govern life. 


Fig. 2: This illustration from Descartes’s Treatise on Man (1664) depicts the “pain pathway.” Descartes described how fire particles “pull” a tube attached to the brain, setting off the pain reaction. He did not realize that the nervous system cannot be reduced to a simple machine.21

Despite its once lofty ambitions, the “automaton” theory of life-as-machine ended in failure when mechanists realized that living creatures could not be mere collections of mechanical parts. How exactly did this happen? To start, mechanism had prompted scientists to discover uniform laws of nature, but the underlying causes for those laws remained a mystery. Empirical science seemed incapable of proving anything about unknown “inner natures” or “essences” of matter, making it possible to postulate hidden forces operating within material objects. This is why 18th century scientists began to explain physical processes in terms of underlying “forces,” “principles,” “kinships,” or “tendencies.” None of these seemed reproducible in a human-made machine. 

More broadly, the new empirical science had encountered a world too complex and too diverse to be explained away with mechanical rules. For instance, the laws of motion seemed ill-equipped to describe the astonishing variety of chemical reactions. Likewise, the functions of living creatures remained too complicated, too wondrous, and too obscure for science to decipher them.22 The limitations of mechanical science therefore implied that there was something unique about living matter, which no one could yet explain, that made it fundamentally different from the parts of an automaton. The hypothesis of life-as-machine had been ostensibly disproven, and the new field of “biology” would have to go in a different direction. Automata would continue to appear in shows and fairs well into the 19th century, but they had become mere novelties, idle distractions rather than stunning displays of cosmic significance.23 

Ironically, 17th century mechanism had destroyed itself on the strength of its own achievements. But this was not truly the end of the mechanical vision overall, of a world defined by immutable laws of nature, where nothing is inherently unknowable. In particular, new technologies such as the microscope held forth the promise that nothing would be permanently hidden from human ingenuity, that everything there is to know could one day be known. 

To some extent, modern science is also a modified and extended version of the mechanistic project, from which it inherited many of its defining characteristics. Most importantly, the new science marginalized God and the soul, directing scientists’ interests instead toward the qualities of matter and the physical laws that govern it. “Spiritualist” and “animist” doctrines would continue to have their place, but material entities and processes became the primary focus of mainstream disciplines, including the life sciences. Having learned from the mistakes of mechanism, “vitalism” and other biological theories would emerge in the 18th century to explain the unique characteristics of living matter.

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Notes

1 Jessica Riskin, “The Defecating Duck, or, the Ambiguous Origins of Artificial Life,” Critical Inquiry 29, no. 4 (June, 2003): 601. 
2 Ibid. 
3 Image taken from “Some Curious Automata,” Scientific American 80, no. 3 (1899): 43.
4 Quoted in Jacques Roger, The Life Sciences in Eigtheenth-Century French Thought, ed. Keith R. Benson, trans. Robert Ellrich (Stanford University Press, 1997).
5 From Descartes’s Treatise of Man, translated P. R. Sloan, as printed in René Descartes, De l’homme et de La Formation Du Foetus, ed. Claude Clerselier (Paris, 1664).
6 This late 17th century definition differed from earlier established usages referring to the “insensible;” this shift is explored in Keith Hutchison, “What Happened to Occult Qualities in the Scientific Revolution?,” Isis 73, no. 2 (1982): 233–53.  
7 For more on the contested history of Aristotelian natural philosophy from the Renaissance until its eventual defeat during the 17th century, see Ann Blair, “Natural Philosophy,” in Cambridge History of Science. Early Modern Science. Vol 3, ed. L. Daston and K. Park (Cambridge University Press, 2006), 365–406. 
8 In the preface to his “Description of the Human Body,” Descartes argues that the soul alone distinguishes a living body from an unmoving corpse, but also that most bodily functions proceed independently of the soul. René Descartes, “Description Du Corps Humain,” in Oeuvres de Descartes, ed. Charles Adam and Paul Tannery, vol. XI (Paris: Léopold Cerf, Imprimeur-Éditeur, 1909), 223-227.
9 Quoted in Sergio Moravia, “From Homme Machine to Homme Sensible: Changing Eighteenth-Century Models of Man’s Image,” Journal of the History of Ideas 39, no. 1 (1978): 46. 
10 René Descartes, “Discourse on the Method,” in Oeuvres de Descartes, ed. Charles Adam and Paul Tannery, vol. VI (Paris: Léopold Cerf, Imprimeur-Éditeur, 1909), 56-59.
11 Daniel Gerber, “Physics and Foundations,” in Cambridge History of Science, Vol.3: Early Modern Science, ed. L. Daston and K. Park (Cambridge University Press, 2006), 62-63.
12 Roger, The Life Sciences, 185. 
13 René Descartes, The Philosophical Writings of Descartes: Volume 1, trans. John Cottingham, Robert Stoothoff, and Dugald Murdoch, vol. 1, The Philosophical Writings of Descartes (Cambridge University Press, 1985), https://books.google.com/books?id=T5cSfRS4m5QC.
14 For more on Descartes’s “hypothetical” method, see Larry Laudan, “The Clock Metaphor and Hypotheses: The Impact of Descartes on English Methodological Thought, 1650-1750,” in Science and Hypothesis (Dordrecht: Springer Netherlands, 1981), 27–58.
15 Lorraine Daston and Katharine Park, Wonders and the Order of Nature, 1150-1750 (New York: Zone Books, 1998), 241. 
16 Leibniz and Lamy are quoted in Roger, The Life Sciences, 163. 
17 Isaac Newton, “General Scholium,” in The Mathematical Principles of Natural Philosophy, trans. Andrew Motte, vol. 2 (London, 1729), 392.
18 Ibid., 393.
19 Roger, The Life Sciences, 371-72. It is also noteworthy that Newton himself was unclear on this issue; he sometimes (but not always) suggested that God was the continual cause of the laws of motion, and that he was therefore always involved in physical processes.
20 Charles T. Wolfe, “On the Role of Newtonian Analogies in Eighteenth-Century Life Science,” in Newton and Empiricism, 2014, 3.
21 Illustration of the pain pathway, from René Descartes, Traité de l’homme, 1662, https://commons.wikimedia.org/wiki/File:Descartes-reflex.JPG
22 As their instruments and techniques improved, mechanists only produced further evidence for the nigh-incomprehensible complexity of living creatures, from tiny insects to the human body. See Roger, The Life Sciences, 177-78, 188-93.
23 See Minsoo Kang, Sublime Dreams of Living Machines (Harvard University Press, 2011), 185-223.

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