This article was last modified on May 5, 2008.

La Mettrie Contra Descartes

I wished to outline briefly the differences between the philosophies of French dualist Rene Descartes and French materialist Julien Offray de La Mettrie. I owe a considerable debt to Gertrude Carman Bussey, who extensively covered La Mettrie’s relationship to other philosophers in his era. Bussey considers La Mettrie’s work “a direct consequence” of Descartes’ system of thought.

Rationalism versus Empiricism

Descartes held that rationalism (truth through reason) was the key to knowledge, whereas La Mettrie accepts empiricism (truth through experience) as the foundation.

Descartes (in Discourse on Method, Part IV) wrote that “neither our imagination nor our senses can give us assurance of anything unless our understanding intervene”.

La Mettrie countered that only our senses are capable of gathering knowledge. He says, “No senses, no ideas. The fewer senses there are: the fewer ideas. No sensations experienced, no ideas. These principles are the necessary consequence of all the observations and experiences that constitute the unassailable foundation of this work.” Also, “The Cartesians would here in vain make an onset upon me with their innate ideas.”

La Mettrie was writing in the tradition of Locke (that our minds start off blank and gain knowledge through experiences), which is the tradition largely accepted today. To say that one school of thought or the other has won the debate, however, would be premature.

Nature of the Soul

Descartes views the soul as a separate entity from the body, guiding it not unlike a pilot would guide a ship (though more closely connected). La Mettrie denies the soul, equating it with the mind, which he sees as a function of the brain.

Descartes (in Discourse on Method, Part V) is quite clear: “The soul is of a nature wholly independent of the body.” But by independent, he does not mean to imply there is no connection whatsoever. “The Reasonable Soul … could by no means be educed from the power of matter … it must be expressly created; and it is not sufficient that it be lodged in the human body, exactly like a pilot in a ship, unless perhaps to move its members, but … it is necessary for it to be joined and united more closely to the body, in order to have sensations and appetites similar to ours, and thus constitute a real man.”

Also, from Meditations, “And certainly the idea I have of the human mind … is incomparably more distinct than the idea of any corporeal object.” (Descartes may use “soul” and “mind” in similar ways… the point, regardless which word he uses, is simply that these are separate aspects of man, not properties of the brain.)

La Mettrie claims, “The diverse states of the soul are therefore always correlative with those of the body.” And also, “The soul and the body fall asleep together.” He equates imagination with soul, saying bluntly that “imagination is the soul”. Leaving him quite confident to say, “The soul is therefore but an empty word.”

Animals as Machines

Descartes asserted that animals are merely machines. Very complex, organic machines, but machines nonetheless. Descartes incorrectly believed that only humans have pineal glands and only humans have minds. This led him to the belief that animals cannot feel pain and the practice of vivisection (dissecting of live animals).

Initially, La Mettrie was opposed to the idea that animals were machines. He calls it an “absurd system” where animals are thought of as such. “An opinion so absurd has never gained admittance among philosophers,” claims La Mettrie. But this early rejection comes from his belief that man and animals are the same, thus there is “no less proof of the faculty of feeling in animals than of feeling in men.”

His position was reversed upon rethinking his observations, and concluded that while he still accepted his basic premise (that men and animals are the same), he took the logic in the opposite direction — that Descartes had not gone far enough. Yes, animals are machines, but so, too, are men machines. (La Mettrie now praises Descartes in this respect, saying he “understood animal nature; he was the first to prove completely that animals are pure machines.”

La Mettrie’s book, Man a Machine, covers his philosophy of materialism and atheism wherein he reduces man to a complex organic machine. I will not recount his arguments for such here, beyond the analogy between men and animals. Also see next section.

Men as Machines

Descartes accepts the human body as something of a machine, but not merely a machine — there is also a soul guiding the machine. La Mettrie denies the soul and accepts the body as a mere machine (albeit a fairly complex one).

Descartes, in Part V of his Discourse on Method, states, “We may easily conceive a machine to be so constructed that it emits vocables, and even that it emits some correspondent to the action upon it of external objects which cause a change in its organs, … but not that it should emit them variously so as appositely to reply to what is said in its presence, as men of the lowest grade of intellect can do.”

La Mettrie responds, “Man is so complicated a machine that it is impossible to get a clear idea of the machine beforehand, and hence impossible to define it.”

La Mettrie’s materialism inevitably leads to determinism, though this was not a path he pursued.

The Properties of Matter

Descartes held that, “The nature of body consists not in weight, hardness, color, and the like but in extension alone — in its being a substance extended in length, breadth and height.” So, the essence of matter is simply that it takes up some physical space.

La Mettrie adds additional attributes to matter. Bussey sums up these additional qualities by stating that matter “is endowed with extensity, the power of movement, and the faculty of sensation.” La Mettrie says the opinion of Descates (that the essence of matter is extension) “has been rejected by all other modern philosophers, … so that the power of acquiring moving force, and the faculty of feeling as well as that of extension, have been from all time considered as essential properties of matter.”

She also points out “that matter has the power of moving itself, and resents any attempt to show that the motion is due to an outside agent.” La Mettrie calls upon the “ancients” who held “that there is no body without a moving force” and that “the substance of bodies [is] composed of two primitive attributes [“the thing which moves” and “the thing which is moved”].

La Mettrie’s view seems unclear at this point. He seems to suggest that a substance cannot be moved without being capable of movement, but he also suggests all substances are capable of movement. Thus, we could simplify this to all things are movable and capable of being moved. I see no reason to suggest the substance itself “resents” the idea that movement comes from outside.

Furthermore, the suggestion that all substances have a “faculty of sensation” seems absurd. We could make the claim (whether or not it is true) that all matter is capable of being sensed, but if he is implying that all matter has the capability to sense we would have to deny this.

On God’s Self-Evidence

God is considered self-evident by a wide range of philosophers, both in the rationalist and empiricist traditions. Locke and Hobbes accepted God’s self-evidence, as does Descartes. La Mettrie denies any such property of God. (Some may cite this as evidence of La Mettrie’s atheism, but that is not necessarily so.)

In his Meditations, Descartes asserts that “I very clearly see that the certitude and truth of all science depends on the knowledge alone of the true God.”

La Mettrie denies that the natural world is evidence of God. “All these evidences of a creator, repeated thousands and thousands of times, evidences that are placed far above the comprehension of men like us, are self-evident (however far one push the argument) only to the anti-Pyrrhonians…” He even goes so far as to suggest life may be completely without purpose. He asks “who can be sure that the reason for man’s existence is not simply the fact that he exists?”

Other Considerations

Bussey draws parallels between La Mettrie and Descartes with regards to numerous other subjects. Some of these include: the warmth of the heart, involuntary movement, bodily humors and the intoxicating effects of wine. I find these issues to be relatively unimportant to the core of each philosopher’s beliefs and do not think there would be much benefit in exploring them further.


La Mettrie, Julien Offray de. Man a Machine. Open Court Publishing, 1993.

Also try another article under Philosophical
or another one of the writings of Gavin.

6 Responses to “La Mettrie Contra Descartes”

  1. Metanoia Says:

    Very informative, not to mention well-written. Thanks!

  2. 444 Says:

    Fantastic stuff, immensely helpful as part of my degree-level essay. A thousand thanks.

  3. Plato Says:

    Absolutely genius, can’t tell you how much this has saved my essay. Whoever wrote this, you are an absolute legend.

  4. shanfov Says:

    Very impressive, thanks so much for this. It would really help me with my college essay

  5. Jenifer Denjen Says:

    renĂ© descartes is definitely the most genius man that ever lived! we think – therefore we are ;-)

  6. Truthsayer Says:

    I would’nt exactly call Descartes a “genius”. The man was seriously delusional as well as a notorious animal abuser. I thouroughly denounce Rene descartes and consider La Mettrie to be his only saving grace. The fact that la mettrie even bothered to lower himself to refute Descarte shows that someone from the time period had enough resolve to speak truth to power. “Nuff said.

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