(Student Guide to World Philosophy)

The French philosopher René Descartes declared that all animals except humans are “machines,” very complicated automata, responding to external stimuli in a mechanical way. Humans alone, because they possess immaterial souls, are conscious and endowed with free will and therefore capable of being virtuous or sinful. However, Julien Offroy de La Mettrie denied the existence of any sharp distinction between humans and other animals. In his Histoire naturelle de l’âme (1745; Treatise on the Soul, 1996), he raised a strong objection to Descartes’s calling brutes “machines,” thereby denying that they think and feel. However, three years later, he changed his terminology (not his doctrine) and argued that animals are machines that feel, and so are humans. “The human body is a machine which winds its own springs; . . . the soul is but a principle of motion or a material and sensible part of the brain.” Man a Machine, the better-known translation of L’Homme-machine, is somewhat of a misnomer. Although in English it seems strange to call a man or a dog a machine, it makes sense to speak of them as mechanisms, which is what La Mettrie meant. Hence his philosophy is often referred to as mechanism.

Body and Soul

(Student Guide to World Philosophy)

Man a Machine is for the most part a treatise on physiological psychology, containing also certain ethical and antitheological reflections. It is in the form of an oration, without subdivisions. La Mettrie begins with a defense of experience and observation as foundations of knowledge even about the soul, as against the claims put forward for revelation as a source superior to reason. “If there is a God, He is the Author of nature as well as of revelation; . . . if there is a revelation, it can not contradict nature.” Although nature certainly stands in need of interpretation, so does the Bible. Concerning the soul, the requisite “experience and observation . . . are to be found throughout the records of the physicians who were philosophers, and not in the works of the philosophers who were not physicians. . . . Only the physicians have a right to speak on this subject.” According to La Mettrie, theologians have the least right.

What experience and observation show the philosopher-physician about the soul is that its character is patently dependent on bodily conditions. When the body is diseased, so is the soul. A genius may be reduced to idiocy by a fever; it sometimes happens, conversely, that “the convalescence of an idiot produces a wise man.” Extreme bodily fatigue produces a sleep amounting to the temporary extinction of the soul. The effects of opium, wine, and coffee are cited. In addition, diet influences character. The English are savage because they eat their meat red and bloody. In La Mettrie’s opinion, the English diet accounts for their vices of “pride, hatred, scorn of other nations, indocility and other sentiments which degrade the character”—but education can counteract this. Extreme hunger and prolonged sexual abstinence can produce raving maniacs. When the body degenerates in old age, so does the soul. Female delicacy and male vigor correspond to the different bodily constitutions of the sexes....

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Nature and Natural Law

(Student Guide to World Philosophy)

It is wrong to try to distinguish humans from other animals by the former’s alleged exclusive acquaintance with natural (moral) law. Natural law is “a feeling that teaches us what we should not do, because we would not wish it to be done to us.” It manifests itself to me when, for example, I feel remorse after bad conduct; my belief that you have a similar experience can only be based on my inferences from your behavior. However, we see the same signs in animals, such as the “crouching and downcast air” of a dog that has offended its master. La Mettrie cites the story of Androcles and the lion to prove that animals feel gratitude. If, however, it is maintained that despite appearances, animals do not really have any awareness of natural law, then it follows that people do not either, for “man is not moulded from a costlier clay; nature has used but one dough, and has merely varied the leaven.” However, in fact, remorse and gratitude are universal, even among the most hardened criminals. These persons commit their atrocities from morbid impulses, and they are punished adequately by their consciences. It would be better to hand them over to doctors than to burn them or bury them alive, as is the custom.

It is clear that for these reasons, virtue is its own reward, and that “Nature has created us all solely to be happy—yes, all of us from the crawling worm to the eagle lost in the clouds.” La Mettrie developed the ethical implications...

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The Mechanical Nature of the Body

(Student Guide to World Philosophy)

Returning to the subject of the soul, La Mettrie next shows that it is not necessary to postulate the soul as a principle or cause of motion of the body because muscular fiber is inherently motile. He offers ten observations and experiments in proof. One is that portions dissected from polyps regenerate into whole polyps; the other nine are concerned either with spontaneous motions of parts of organisms severed from bodies or with the motion of parts of the body after death. “The soul is therefore but an empty word, of which no one has any idea, and which an enlightened man should use only to signify the part in us that thinks.”

La Mettrie describes at considerable length the physiology of reflex and involuntary movements to illustrate the mechanical nature of the body. He cites, among other things, the phenomenon of erection. The bodily effects of emotional states show, moreover, that there is no sharp division between what is under control of the will and what is not. Though La Mettrie does not deny (or even discuss) the “freedom of the will,” he remarks that the will “cannot act save by permission of the bodily conditions.” However, having shown (to his satisfaction) that the body is self-moved and that consciousness is a property of its organized matter, not an independent substance, La Mettrie confesses that he can go no further in explanation. “The nature (origin) of motion is as unknown to us as that of matter.”


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(Student Guide to World Philosophy)

La Mettrie concludes by picturing the wisdom, justice, tranquillity, reverence (for nature), gratitude, affection, tenderness, kindliness, pity, and forgiveness—in a word, the happiness—of the materialist.Convinced, in spite of the protests of his vanity, that he is but a machine or an animal, the materialist will not maltreat his kind, for he will know too well the nature of those actions, whose humanity is always in proportion to the degree of the analogy proved between human beings and animals; and following the natural law given to all animals, he will not wish to do to others what he would not wish them to do to him. Let us then conclude boldly that man is a machine, and that in the whole universe there is but a single substance differently modified. . . . Such is my system, or rather the truth, unless I am much deceived. It is short and simple. Dispute it now who will.

More than two centuries after La Mettrie, one is likely to smile wryly at the pretty picture of grateful lions regulating their conduct by the Golden Rule, and at the conviction that once religion is gone, all will be well—as if religion were something imposed on people from outside, contrary to “the spontaneous dictates of their own being.” However, these amiable eighteenth century ideas should not deceive anyone into supposing that La Mettrie was a naïve thinker. He deserves the credit (or blame) for many insights usually attributed to such philosophers as Jean-Jacques Rousseau, Étienne Bonnot de Condillac, Claude-Adrien Helvétius, and Paul-Henri-Dietrich d’Holbach. His brief remarks on the relation of evidence to conclusion in the design argument for the existence of God penetrate to the essential logical point in a manner not inferior to the more celebrated critiques of David Hume and Immanuel Kant.

Materialists, at least since Lucretius, argued that no chasm separates humans from the rest of nature and that the soul must be material, or a property of matter, because mental states obviously vary with the condition of the body. La Mettrie did not have a new argument; he only added to the old one such evidence as was available to him from recent investigations of brain anatomy. However, just as La Mettrie questioned the relevance of piling up evidence for design in nature for the purpose of proving a Great Designer, so here also one can ask whether more and more detail about the dependence of soul on body strengthens the conclusion that soul...

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(Student Guide to World Philosophy)

Additional Reading

Brehier, Emile. The History of Philosophy. Vol. 5 in The Eighteenth Century. Translated by Wade Baskin. Chicago: University of Chicago Press, 1967. Contains a short but sound discussion of the development of materialism in the middle of the eighteenth century.

Rosenfield, Leonora Cohen. From Beast-Machine to Man-Machine: Animal Soul in French Letters from Descartes to La Mettrie. 1940. Rev. ed. New York: Octagon Books, 1968. This older volume is indispensable for the understanding of the progression of mechanism.

Wellman, Kathleen Anne. La Mettrie: Medicine, Philosophy, and Enlightenment. Durham, N.C.: Duke University Press, 1992. Gives medical background of Julien Offroy de La Mettrie’s philosophical views.