“What vices, says Augustine, have not been approved of? What virtues have not been condemned in different centuries? This father of the church, here more of a philosopher than a theologian, has no difficulty in inferring that human reason is too powerless, too incapable of judging the nature of things, to be able to decide the great question of vices and virtues. This, I believe, is tantamount to saying quite clearly that good and evil possess no specific signs to characterize them absolutely and that they can be distinguished from each other only by the interests of society (a truth which can never be taught enough). Remove this support, and farewell morality! Vices and virtues are absolutely indiscernible, to use Leibniz’s unpleasant word. Such is natural equality. If anyone has another conception of it, I would be glad if he would give it to me.”

— Julien la Mettrie (1751), “Anti-Seneca” (pgs. 131-32)

“The atheist d’Holbach labeled La Mettrie ‘insane’, while Diderot described him as ‘frenetic’ and was clearly disgusted with his ethical views.”

— Martin Staum (2014), Cabanis: Enlightenment and Medical Philosophy in the French Revolution (pgs. 69-70)

“The notion that the brain itself feels and thinks is a ‘revolting opinion’ reminiscent of the ‘insane [see: crazy] author [Holbach] of the Systéme de la Nature’.”

— Mathieu Buisson (c.1802) (Ѻ), as cited by L.S. Jacyna (1987) in summary of Buisson’s criticism (Ѻ)(Ѻ) of Xavier Bichat’s 1801 theory (Ѻ) of physiological properties; note: quoted misattributed, by Jennifer Hecht (2003), to Louis de Bonald

See: Genius hiatus effect

“During the campaign of Freiburg, La Mettrie had an attack of violent fever. For a philosopher an illness is a school of physiology; he believed that he could clearly see that thought is but a consequence of the organization of the machine, and that the disturbance of the springs has considerable influence on that part of us which the metaphysicians call soul. Filled with these ideas during his convalescence, he boldly bore the torch of experience into the night of metaphysics; he tried to explain by aid of anatomy the thin texture of understanding, and he found only mechanism where others had supposed an essence superior to matter. He had his philosophic conjectures printed under the title of “The Natural History of the Soul.” The chaplain of the regiment sounded the tocsin against him, and at first sight all the devotees cried out against him.”

“The soul is merely a vain term of which we have no idea and which a good mind should use only to refer to that part of us which thinks.”

— Julien la Mettrie (1747), Man: a Machine (pg. 26) (Thomson translation)

“What is the soul, but an empty word to which no idea corresponds?”

La Mettrie asserts that because the body "moves according to its own principle", without its head, as evidenced by the ability of the body of a Turkey's to move about, without a head or brain, the location of the soul, as believed in his day, that the animal soul doesn't exist, and hence, as humans are part of the animal kingdom, so also the human soul does not exist, but is only a vain word for the thinking part of humans.

“Given the slightest principle of movement, animate bodies will have everything they need to move, feel, think, repent and, in a word, behave in the physical sphere and in the moral sphere which depends on it. None of this is mere supposition. Those who believe that all the difficulties hate not yet been removed will find here a list of experiments which will completely satisfy them.

1. All animal flesh palpitates after death and the more cold-blooded the animal is and the less it perspires, the longer the flesh palpitates. Tortoises, lizards, snakes, etc. prove this.
2. When separated from the body, the muscles retract when they are pricked.
3. The bowels retain for a long rime their peristaltic or vermicular movement.
4. A simple injection of warm water reanimates the heart and the muscles, according to Cowper. [N1]
5. A frog's heart, particularly when left in the sun, or even better on a warm table or a plate, moves for an hour or more after having been removed from the body. If the movement seems to have vanished beyond recovery, you only need to prick the heart and this hollow muscle still beats. William Harvey has made the same observation concerning toads. [N2]
6. Francis Bacon, a first-class author, speaks in his History of Life and Death of a man convicted of treason whose heart was torn out while he was still alive, and thrown into the flames; this muscle first leapt vertically to a height of one and a half feet, but then, losing force, it leapt less high each time, for seven or eight minutes. [N3]
7. Take a chick still in its egg and tear out its heart: you will observe the same phenomena in more or less the same circumstances. The warmth of one's breath alone reanimates an animal on the point of death in a pneumatic engine. The same experiments that we owe to Boyle and Steno39 can be done on pigeons, dogs, rabbits, pieces of whose hearts move just like whole hearts. The same movement can be seen in the torn-off paws of moles.
8. Caterpillars, worms, spiders, flies and eels give rise to the same observations, and the movement in the cut-off parts increases in hot water because of the fire it contains.
9. A drunken soldier cut off the head of a turkey-**** with a sabre. The animal stayed upright, then it walked and ran; when it hit a wall it turned round, beat its wings, still running, and finally fell down. Even when it was on the ground, all this ****'s muscles continued to move. That is what I saw, and it is easy to see more or less the same phenomena in kittens or puppies whose heads have been cut off.
10. Polyps do more than move after being cut up: within a week each piece generates a new animal. I am sorry for the way this affects the naturalists' theory of reproduction; or rather I am pleased, because this discovery teaches us never to draw general conclusions, even from all the most decisive experiments ever known.

I have given many more facts than are needed to prove beyond all doubt that each tiny fiber or part of organized bodies moves according to its own principle, whose action does not depend, like voluntary movements, on the nerves; this is because the movements in question happen without the part which undergoes them being in contact with the circulation. Now, if this force can be observed even in the pieces of fibers, the heart, which is a particularly complex structure of fibers, must have the same property.”

”The principle of motion in whole bodies or in parts cut into pieces is such that it produces movements which are not, as has been thought, disordered, but completely regular, both in warm whole animals and in cold incomplete ones.”

A French-English edition of la Mettrie's Man a Machine or Human Machine.

“[Dualism] is a trick of skill, a ruse of style, to make theologians swallow a poison.”

“It thus appears that there is but one type in the universe, and that man is the most perfect example. He is to the ape, and to the most intelligent animals, as the planetary pendulum of Huygens is to a watch of Julien Leroy. More instruments, more wheels, and more springs were necessary.”

“M. La Mettrie after losing sight of his hospitals and his patients, gave himself up completely to speculative philosophy; he wrote his Man a Machine or rather he put on paper some vigorous thoughts about materialism, which he doubtless planned to rewrite. This work, which was bound to displease men who by their position are declared enemies of the progress of human reason, roused all the priests of Leyden against its author. Calvinists, Catholics and Lutherans forgot for the time that consubstantiation, free will, mass for the dead, and the infallibility of the pope divided them: they all united again to persecute a philosopher who had the additional misfortune of being French, at a time when that monarchy was waging a successful war against their High Powers.”

“The human body is a self-winding machine, a living representation of perpetual motion in which the motive force resides in the very substance of the parts, not including the veins, arteries, and nerves, in short, the organization of the entire body. Each part contains in itself springs whose forces are proportioned to its needs.”

“We do not know nature at all; causes hidden deep within her may have produced everything. Look in your turn at Trembley’s polyp! Does it not contain inside it the causes of its own regeneration? Why then would it be absurd to believe that there exist physical causes for which everything was made and to which the whole chain of this vast universe is so necessarily linked and subordinated that nothing that happens could not have happened; that it is our absolutely invincible ignorance of these causes that has made us look to a god, who is not even a being of reason, according to some? Thus, destroying chance does not mean proving the existence of a supreme being, for there may be something else which is neither chance nor god; I mean ‘nature’, the study of which can as a result only produce unbelievers, as is proved by the manner of thinking of all its most successful observers.”

— Denis Diderot (c.1745), Philosophical Thoughts; cited by Julien la Mettrie (1747) in Man: a Machine (pg. 24)

“The universe will never be happy unless it is atheistic.”

— French Pyrrhonian (c.1745), said to his friend Julien la Mettrie; quoted in Man: a Machine (pg. 25)

“La Mettrie had much genius and imagination, who advanced in the career of science at a giant’s pace; but he suffered from jealously, and his quick temper made him too susceptible to it.”

— Frederick the Great (1751), “Eulogy on Julien Offray de la Mettrie” [4]

“Mettrie expressed his heretical views publicly in two tracts published in 1745, Natural History of the Soul, and in 1748, Man as Machine. With these two arrows aimed at the priests, La Mettrie declared that human beings are soulless automata, like animals of Descartes’ system.”

— Julien Musolino (2015), The Soul Fallacy (pg. 151) [4]

“There are very good reasons indeed to believe that materialism is true and that Julien de La Mettrie was a visionary. If there is no positive evidence supporting dualism, if modern science renders the doctrine untenable, if it is explanatorily impotent, and if all the evidence points toward materialism instead, then it is time to acknowledge what reason is trying to tell us—there is most likely no soul.”

— Julien Musolino (2015), The Soul Fallacy (pg. 154) [4]

“Since diseases of the brain, according to the place where the attack, destroy sometimes one sense and sometimes another, are those who place the soul in one of the pairs of the optic lobes any more wrong than those who would like to limit it to the oval center, the corpus callosum (Giovanni Lancisi, 1713), or even the pineal gland (Descartes, c.1620)?”

— Julien la Mettrie (1745), Treatise on the Soul (pg. 65); note: Johann Helmont placed the soul in the pylorus, Aristotle place the soul in the heart, and William Harvey placed the soul in the blood (Ѻ)

“For a wise man, it is not enough to study nature and truth; he must dare to proclaim it for the benefit of the small number of those who are willing and able to think; for the others, who are the willing slaves of prejudice are no more capable to of reaching the truth than are flying frogs.”

— Julien la Mettrie (1747), Man: a Machine (pg. 3)

“The more ferocious animals are, the less brain they have.”

— Julien la Mettrie (1747), Man: a Machine (pg. 10)

“In the same way as a violin string or harpsichord key vibrates and gives out a sound, so the strings of the brain, struck by rays of sound, are stimulated to give out or repeat the words which touch them.”

— Julien la Mettrie (1747), Man: a Machine (pg. 14)

“Break the chains of your prejudices and take up the torch of experience, and you will honour nature in the way she deserves, instead of drawing derogatory conclusions from the ignorance in which she has left you. Simply open your eyes and ignore what you cannot understand, and you will see that a laborer whose mind and knowledge extend no further than the edges of his furrow is no different essentially from the greatest genius, as would have been proved by dissecting the brains of Descartes and Newton; you will be convinced that the imbecile or the idiot are animals in human form, in the same way as the clever ape is a little man in another form; and that, since everything depends absolutely on differences in organization, a well-constructed animal who has learned astronomy can predict an eclipse, as he can predict recovery or death when his genius and good eyesight have benefited from some time at the school of Hippocrates and at patients' bedsides.”

— Julien la Mettrie (1748), The Human Machine (Ѻ)

“We can see that there is only one substance in the universe and that man is the most perfect one. He is to the ape and the cleverest animals what Huygens's planetary clock is to one of Julien Leroy's watches. If it took more instruments, more cogs, more springs to show or tell the time, if it took Vaucanson more artistry to make his flautist than his duck, he would have needed even more to make a speaking machine, which can no longer be considered impossible, particularly at the hands of a new Prometheus. Thus, in the same way, nature needed more artistry and machinery to construct and maintain a machine which could continue for a whole century to tell all the beats of the heart and the mind; for we cannot tell the time from the pulse, it is at least the barometer of heat and liveliness, from which we can judge the nature of the soul.”

— Julien la Mettrie (1748), The Human Machine (Ѻ)

“Descartes and all the Cartesians, among whom the followers of Malebranche have long been numbered, have made the same mistake. They have taken for granted two distinct substances in man, as if they had seen them, and positively counted them.”

— Julien La Mettrie (1748), The Human Machine [4]

“Let him who so wishes take pleasure in boring us with all the wonders of nature: let one spend his life observing insects, another counting the tiny bones in the hearing membrane of certain fish, even in measuring, if you will, how far a flea can jump, not to mention so many other wretched objects of study; for myself, who am curious only about philosophy, who am sorry only not to be able to extend its horizons, active nature will always be my sole point of view; I love to see it from afar, in its breadth and its entirety, and not in specifics or in little details, which, although to some extent necessary in all the sciences, are generally the mark of little genius among those who devote themselves to them.”

— Julien la Mettrie (c.1747), The Human Plant (Ѻ)

“There is nothing weird or strange for the nature. It’s people who ascribe to her various oddities.”

— Julien la Mettrie (c.1745) (Ѻ)

“Humanity will not be happy until it is atheistic.”

— Julien la Mettrie (c.1748) (Ѻ)

“They have spiritualized matter rather than 'materializing' the soul.”

— Julien la Mettrie (c.1748), the “incomprehensible” monadism of Leibniz and his supporters

“Man is a machine and in the whole universe there is but a single substance, matter, variously modified.”

— Julien la Mettrie (c.1748) (Ѻ)

“Perhaps minerals are formed according to the laws of attraction, so that iron never attracts gold nor gold iron, all heterogeneous parts repel each other and only homogeneous parts unite or form a single body together. But without deciding anything in the obscurity which covers all sorts of reproduction, should I, because I do not know how fossils are formed, call on, or rather suppose, a soul to explain the formation of bodies.”

— Julien la Mettrie (1748), “Man as Plant” (pg. 84)

“Do we need to resort to a soul to explain plants’ growth, which is infinitely faster than that of stones? And in the vegetation of all bodies, from the softest to the hardest, surely everything is determined by nourishing fluids, which are more or less terrestrial and applied with differing degrees of force to more or less hard masses? From which I can indeed see that a stone must grow less in a hundred years than a plant does in a week.”

— Julien la Mettrie (1748), “Man as Plant” (pg. 84)

“We must forgive the ancients for their general and particular souls; for lack of experimental physics and anatomy, they were not at all versed in the structure and organization of bodies. Everything must have been as incomprehensible to them as to children or savages seeing a watch for the first time; knowing nothing of its springs, they think it to be animated or endowed with a soul like them, while it is enough to glance at the artifice of this machine; it is a simple artifice which really implies, not the possession of its own soul, but the soul of an intelligent workman without whom chance would never have been able to indicate the time and the sun’s passage.”

— Julien la Mettrie (1748), “Man as Plant” (pgs. 84-85)

“We are much more enlightened by physics, which shows us that there is no other soul of the world than god and movement, and no other soul of plants than heat.”

— Julien la Mettrie (1748), “Man as Plant” (pg. 85)

“Man is, above all the beings hitherto known, the one which has the most soul, as if it were necessary for that to be so; and the plant is likewise the one which has, and was destined to have, the least of all, if we exclude minerals.”

— Julien la Mettrie (1748), “Man as Plant” (pg. 85)

“After the vegetables and the minerals – bodies without a soul – come beings which begin to be animate, such as the polyp and all the animal-plants still unknown to today, which other favored Trembleys will discover in time.”

— Julien la Mettrie (1748), “Man as Plant” (pg. 85)

“If all bodies are moved by fire, what gives fire its movement? Ether. What gives it to ether? Diderot is right: our philosophy is no better than the Indians.”

— Julien la Mettrie (1750), “The System of Epicurus” [N4]

“Here are some incontrovertible facts. People are dying of hunger at sea, who eat the one among their companions who is sacrificed by lot, experience no more remorse than cannibals do. Such is habit and such is need, thanks to which anything is allowed. When I see our executioners hanging, breaking on the wheel, burning and torturing their fellow beings, I can feel inside myself something which is in revolt; I seem to hear a voice groaning in the depths of my heart: ‘oh nature, or humanity, you are only an empty word if by these actions you are not violated – no that is not enough – if you are not turn apart while obeying the law’. But no, criminals have executioners and executioners have none; their hearts are closed to remorse and repentance. And yet they are murderers! Yes, but stipended murderers, in the same way as idolaters were and perhaps still are sacred murders. They ones are paid and the others are revered. Is a man who, dying of hunger, is forced to slit a traveler’s throat, any more guilty than a man who strangles a criminal on the orders of judges? Whether one is forced by justice or forced by misery, surely one is still forced?”

— Julien la Mettrie (1751), “Anti-Seneca” (pg. 136)

“Lycurgus had weak and unhealthy children drowned and was proud of his wisdom. Look at Plutarch’s account of his life, and you will see at Sparta they knew neither modesty, nor robbery, nor adultery, etc.”

— Julien la Mettrie (1751), “Anti-Seneca” (pg. 136)