Lecture 5: Man the Machine

Foundations of Liberty
The Intellectual Crisis of the Modern World

A Lecture Series with Prof. Thomas Patrick Burke

In the last lecture we saw that the new science that began to emerge in 1600 abandoned the search for Socratean and Aristotelian teleological explanation,  not only for the inanimate world, but also for living beings. In both domains the new science seeks only mechanistic explanations. In addition we saw that this mechanicism or mechanistic reductionism does not come from the nature of the world, it is not the result of anything discovered by science in the world, but originates from science’s own method, specifically from its twofold requirement that explanations should be parsimonious and should make verifiable predictions.  In other words, it is nothing more than an assumption.  An assumption for a practical reason, no doubt, but still only an assumption, not a belief resting on an objective foundation.  In this lecture we turn to some of the changes that have taken place as a result of this assumption in our view of other living beings and ourselves. The essential change took place quickly.



In 1637 Descartes published his Discourse on the Method of Rightly Conducting the Reason and Seeking for Truth in the Sciences.  The first step in his method (as he describes it autobiographically) was to “sweep completely away” all his former opinions and try to rebuild them on what he considered a rational foundation. One of these opinions concerned animals. In their regard Descartes was not just an armchair philosopher. He maintained a dissection room, and has evidently done a great deal of hands-on research and experimentation on animal bodies, including vivisection. He has cut open hearts he held in his hand while they were still beating, he says. He reports that “one sees that heads, for a little while after being cut off, continue to move and bite the earth, in spite of the fact that they are no longer animated.” But this continued movement is not surprising, he contends. “None of this will seem strange to those who know how many varieties of automata, or moving machines, human industry can make, by using only very few pieces in comparison with the huge number of bones, muscles, nerves, arteries, veins, and all the other parts in the body of each animal.”   He realized that “if there were machines which had the organs and the external shape of a monkey or of some other animal without reason, we would have no way of recognizing that they were not exactly the same nature as the animals…”  He concludes that animals are in fact mere machines. They do not have mind, reason or even consciousness. It is true they sometimes appear to behave intelligently, and even more intelligently than we ourselves do, but if that were really true they would always behave that way, whereas in fact they only do so on certain occasions.  Descartes deduces that “…they have no reason at all, and that it is nature which has activated them according to the arrangement of their organs—just as one sees that a clock, which is composed only of wheels and springs, can keep track of the hours and measure time more accurately than we can, for all our care.”

The movements of animals are due to the change of form of muscles, which shorten and become thicker; and this change of form in a muscle arises from a motion of the substance contained within the nerves which go to the muscle.

Moreover, we know that all the movements of the limbs depend on the muscles, and that these muscles are opposed to one another in such a manner, that when one of them shortens, it draws along the part of the body to which it is attached, and so gives rise to a simultaneous elongation of the muscle which is opposed to it. Then, if it happens afterwards that the latter shortens, it causes the former to elongate, and draws towards itself the part to which it is attached. Lastly, we know that all these movements of the muscles, as all the senses, depend on the nerves, which are like little threads or tubes, which all come from the brain, and, like it, contain a certain very subtle air or wind, termed the animals spirits.  (Passions of the Soul, Art. vii.)

The sensations of animals are due to a motion of the substance of the nerves which connect the sensory organs with the brain.

It is the little threads of which the inner substance of the nerves is composed which provide sensation. You must conceive that these little threads, being enclosed in tubes, which are always distended and kept open by the animal spirits which they contain, neither press upon nor interfere with one another and are extended from the brain to the extremities of all the members which are sensitive–in such a manner, that the slightest touch which excites the part of one of the members to which a thread is attached, gives rise to a motion of the part of the brain whence it arises, just as by pulling one of the ends of a stretched cord, the other end is simultaneously moved. . . .   (Dioptrics, Fourth Discourse).

Human Beings


Human beings are not animals. Unlike them, we have a mind, reason and consciousness. This is because there are in the universe two radically different kinds of substance.  There is matter, which is characterized by extension, res extensa. And there is mind, a thing which thinks, res cogitans. I think, therefore I am. Cogito, ergo sum. Animals are only matter. A human being, by contrast,  is a mind in matter. But the human body is just like an animal: it is simply matter, and is a machine. A human being is therefore a mind in a machine. We are to imagine a clock inhabited by a mind.

Out of his experiments on animals he has developed a theory of how a mind and a machine can be united into one being.  This union of two completely different kinds of substance takes place in the brain, through the nerves and the pineal gland.

It was an important step towards this conclusion that he first relocated all sensation, thought and emotion from the heart, where they had previously been placed since time immemorial, to the brain. That is to say, some change in the condition of the brain, he believed, invariably preceded the state of consciousness designated by each of these terms.


Although the soul is united to the whole body, its principal functions are, nevertheless, performed in the brain; it is here that it not only understands and imagines, but also feels; and this is effected by the intermediation of the nerves, which extend in the form of delicate threads from the brain to all parts of the body, to which they are attached in such a manner, that we can hardly touch any part of the body without setting the extremity of some nerve in motion. This motion passes along the nerve to that part of the brain which is the common sensorium, as I have sufficiently explained in my ‘Treatise on Dioptrics;’ and the movements which thus travel along the nerves, as far as that part of the brain with which the soul is closely joined and united, cause it, by reason of their diverse characters, to have different thoughts. And it is these different thoughts of the soul, which arise immediately from the movements that are excited by the nerves in the brain, which we properly term our feelings, or the perceptions of our senses. (Principles of Philosophy §169)

But as regards the souls of beasts, although this is not the place for considering them, and though, without a general exposition of physics, I can say no more on this subject than I have already said in the fifth part of my Treatise on Method; yet, I will further state, here, that it appears to me to be a very remarkable circumstance that no movement can take place, either in the bodies of beasts, or even in our own, if these bodies have not in themselves all the organs and instruments by means of which the very same movements would be accomplished in a machine. So that, even in us, the spirit, or the soul, does not directly move the limbs, but only determines the course of that very subtle liquid which is called the animal spirits, which, running continually from the heart by the brain into the muscles, is the cause of all the movements of our limbs, and often may cause many different motions, one as easily as the other.

And it does not even always exert this determination; for among the movements which take place in us, there are many which do not depend on the mind at all, such as the beating of the heart, the digestion of food, the nutrition, the respiration of those who sleep; and even in those who are awake, walking, singing, and other similar actions, when they are performed without the mind thinking about them. And, when one who falls from a height throws his hands forward to save his head, it is in virtue of no ratiocination that he performs this action; it does not depend upon his mind, but takes place merely because his senses being affected by the present danger, some change arises in his brain which determines the animal spirits to pass thence into the nerves, in such a manner as is required to produce this motion, in the same way as in a machine, and without the mind being able to hinder it. Now since we observe this in ourselves, why should we be so much astonished if the light reflected from the body of a wolf into the eye of a sheep has the same force to excite in it the motion of flight?

After having observed this, if we wish to learn by reasoning, whether certain movements of beasts are comparable to those which are effected in us by the operation of the mind, or, on the contrary, to those which depend only on the animal spirits and the disposition of the organs, it is necessary to consider the difference between the two, which I have explained in the fifth part of the Discourse on Method (for I do not think that any others are discoverable), and then it will easily be seen, that all the actions of beasts are similar only to those which we perform without the help of our minds. For which reason we shall be forced to conclude, that we know of the existence in them of no other principle of motion than the disposition of their organs and the continual affluence of animal spirits produced by the heat of the heart, which attenuates and subtilises the blood; and, at the same time, we shall acknowledge that we have had no reason for assuming any other principle, except that, not having distinguished these two principles of motion, and seeing that the one, which depends only on the animal spirits and the organs, exists in beasts as well as in us, we have hastily concluded that the other, which depends on mind and on thought, was also possessed by them. (Meditations, Responses to the Fourth Set of Objections)


In 1687 Isaac Newton (1643-1727) published his Mathematical Principles of Natural Philosophy(Philosophiae Naturalis Principia Mathematica).  In this work he proposed three sets of mathematical equations:

  1. a) three laws of motion, which established a new science, mechanics, the foundation of modern physics (1, the law of inertia discovered by Galileo, that every body persists in its state of rest or uniform motion unless it is subjected to an external force; 2, a body subjected to an external force changes its momentum proportionately to the force; and 3, to every action there is an equal and opposite reaction.)
  2. b) the law of universal gravitation he had formulated:  all bodies are attracted to one another by a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
  3. c) how these laws give rise to the orbits of the planets, as they had been discovered by Kepler.

The effect of this book was to transform, as it appeared to many, not only individual animals and men, but the entire universe, into a single gigantic machine. With these equations Newton made it possible in principle to predict with exactitude, it seemed, all the future movements of all bodies in the universe.  If at any time in the history of the world we knew just where everything was, we could calculate just where everything would be at any other given time. Soon the idea of the “clockwork universe” was accepted throughout Europe. God, who in the Aristotelian universe had been considered an intrinsic part of the daily operation of the universe, continually supplying the motion that kept it going, was suddenly reduced to the role of merely winding the clock up at the beginning, and he could then, as it were, go back to sleep, leaving it to take care of itself. This was the philosophy of Deism.

Newton himself did not personally go along with this vast reduction in the role of God. He considered God was still necessary to fill certain unexplained gaps, for example certain irregularities in the orbits of the planets.  But at this point most of his followers gave up following him, concluding quite rightly that the gaps would eventually be filled by science.

Since the whole universe was a giant machine, everything in it must also be a machine, it was felt, including animals and human beings.

De la Mettrie

Some 20 years after Newton’s death, in 1748, Julien Offray de la Mettrie published Man The Machine  (L’Homme Machine).  This book is much more radical than either Descartes or Newton. Descartes believed there were two basically different kinds of substance in the world: matter and mind. Animals were purely matter, and so were purely mechanical and had no mind, but man possessed both and was a mind inhabiting a machine.  Both Descartes and Newton believed in God and an afterlife. Mettrie’s mechanicism goes further. There is only one kind of substance in the world and it is matter. It is true that living things have the power to move themselves, but what we call life or mind is nothing more than a particular organization of matter.  Life itself is a machine. About God and an afterlife, possibly even for animals,  Mettrie professes to be agnostic.

The decisive fact for his thoroughgoing mechanicism was his observation that living beings continue to move themselves even after they are dead. He gives the following list, largely deriving from his own investigations:

  1. The flesh of all animals palpitates after death. This palpitation continues longer, the more cold blooded the animal is and the less it perspires. Tortoises, lizards, serpents, etc. are evidence of this.
  2. Muscles separated from the body contract when they are stimulated.
  3. The intestines keep up their peristaltic or vermicular motion for a long time.
  4. According to Cowper, a simple injection of hot water reanimates the heart and the muscles.
  5. A frog’s heart moves for an hour or more after it has been removed from the body, especially when exposed to the sun or better still when placed on a hot table or chair. If this movement seem totally lost, one has only to stimulate the heart, and that hollow muscle beats again. Harvey made this same observation on toads.
  6. Bacon of Verulam in his treatise Sylva Sylvarum cites the case of a man convicted of treason, who was opened alive, and whose heart thrown into hot water leaped several times, each time less high, to the perpendicular height of two feet.
  7. Take a tiny chicken still in the egg, cut out the heart and you will observe the same phenomena as before, under almost the same conditions. The warmth of the breath alone reanimates an animal about to perish in the air pump. The same experiments, which we owe to Boyle and to Stenon, are made on pigeons, dogs, and rabbits. Pieces of their hearts beat as their whole hearts would. The same movements can be seen in paws that have been cut off from moles.
  8. The caterpillar, the worm, the spider, the fly, the eel – all exhibit the same phenomena; and in hot water, because of the fire it contains, the movement of the detached parts increases.
  9. A drunken soldier cut off with one stroke of his sabre an Indian rooster’s head. The animal remained standing, then walked, and ran: happening to run against a wall, it turned around, beats its wings still running, and finally fell down. As it lay on the ground, all the muscles of this rooster kept on moving. That is what I saw myself, and almost the same phenomena can easily be observed in kittens or puppies with their heads cut off.
  10. Polyps do more than move after they have been cut in pieces. In a week they regenerate to form as many animals as there are pieces.

…As to the development of feeling and motion, it is absurd to waste time seeking for its mechanism. The nature of motion is as unknown to us as that of matter.

…Grant only that organized matter is endowed with a principle of motion, which alone differentiates it from the inorganic …and that among animals, as I have sufficiently proved, everything depends upon the diversity of this organization: these admissions suffice for guessing the riddle of substances and of man. It thus appears that there is but one type of organization in the universe, and that man is the most perfect example.

…Let us not say that every machine or every animal perishes altogether or assumes another form after death, for we know absolutely nothing about the subject….Let us then submit to an invincible ignorance on which our happiness depends.

Mettrie is optimistic about the effects of his materialism and mechanicism: it will necessarily produce both goodness and happiness.

He who so thinks will be wise, just, tranquil about his fate, and therefore happy. He will await death without either fear or desire, and will cherish life (hardly understanding how disgust can corrupt a heart in this place of many delights); he will be filled with reverence, gratitude, affection, and tenderness for nature, in proportion to his feeling of the benefits he has received from nature; he will be happy, in short, in feeling nature, and in being present at the enchanting spectacle of the universe, and he will surely never destroy nature either in himself or in others.

More than that! Full of humanity, this man will love human character even in his enemies. Judge how he will treat others. He will pity the wicked without hating them; in his eyes, they will be but mis-made men. But in pardoning the faults of the structure of mind and body, he will nonetheless admire the beauties and the virtues of both. Those whom nature shall have favored will seem to him to deserve more respect than those whom she has treated in step-motherly fashion. Thus, as we have seen, natural gifts, the source of all acquirements, gain from the lips and heart of the materialist, the homage which every other thinker unjustly refuses them.

Let us then conclude boldly that man is a machine, and that in the whole universe there is but a single substance differently modified.

Mettrie was victorious. His worldview is exactly that of science today. Its optimism, however, is no longer so hearty.

[1] Huxley, “On the Hypothesis that Animals Are Automata, and Its History” (1874)

Collected Essays I.