QuestionsIs the mind the brain?Man is a machine that winds its own springs
Is the mind the brain?The mind comes from matter

Man is a machine that winds its own springs

Man a Machine

Julien Offray de La Mettrie 1709 · 1751Man is a machine: the soul is only the working of the body.
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What it claims

The soul is only a word for the part of the body that thinks, and man as a whole is a machine, the most perfect of all.

Why

The state of the soul always follows that of the body (sleep, opium, food, fever): the soul is just the body at work.

The same idea through history
René Descartes1637Descartes holds animals to be pure machines (a clock has no mind), but keeps the soul for man alone.
Julien Offray de La Mettrie1747La Mettrie removes the exception: man too is a machine, only a more complicated one, and the soul is just the part that thinks.
In short

"Man is a machine that winds its own springs" is an argument by Julien Offray de La Mettrie (Man a Machine, 1747, 1747) on the question "Is the mind the brain?" (answer: the mind comes from matter). Its claim: The soul is only a word for the part of the body that thinks, and man as a whole is a machine, the most perfect of all. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P3, P6). AskPhilosophy presents 3 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

Man a Machine, 1747
Valid with an implicit premise

A glass of wine, a sleepless night, a dose of opium: and thought changes, sometimes even the will. As a physician, La Mettrie draws a blunt conclusion. If the soul depends on the body that much, it is nothing but the body's working. Descartes had already said that animals are machines; La Mettrie adds that man is one too, the most perfect. The book caused a scandal: it was burned in Leiden, and the author had to take refuge at the court of Frederick II.

P1Sleep shows that the soul follows the body: when the blood calms down, the soul grows heavy with the eyelids, and in sleep it is as if it were not.
P2Opium, wine, food and fever change the soul down to its will: without food it pines away, goes mad and dies.
P3 · implicit premiseIf the state of the soul follows the state of the body in this way, in every case, then the soul is nothing but the working of the organised brain and body: no distinct substance is needed.
P4Animals are machines (Descartes himself admits it), and their body winds its own springs: food keeps up what fever excites.
P5Man differs from animals only in degree: a few more wheels and springs, a more developed brain. He is to the ape what Huygens's pendulum clock is to an ordinary watch.
P6 · implicit premiseWhat differs only in degree is of the same nature: if animals are machines, man is one too.
Therefore the soul is only a word for the part of the body that thinks, and man as a whole is a machine, the most perfect of all.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P3, the computer finds a case where the soul's state always follows the body's, and yet the soul is something other than the body. For example, a pilot whose movements depend entirely on the state of his plane (he can do nothing if the engine fails) is not therefore a part of the plane. Without P6, man can be of a different nature from animals, even if the difference seems only one of degree.
The argument is valid once two hidden premises are added. P3 is the biggest leap: La Mettrie goes from "the soul depends on the body" to "the soul is only the body at work". He almost writes it ("they are visibly only this organisation itself"), but does not prove it. A dualist can accept P1 and P2 and reject P3: dependence is not identity. P6 is a rule of economy: it assumes that a difference of degree hides no difference of kind. Descartes rejects it, for speech and reason (see the objections).
Analogy. Look at a clock: the more wheels it has, the more it can do (tell the hour, the date, the course of the planets). No one thinks you must add a "spirit of the clock" to go from a simple watch to a learned clock. La Mettrie says the same of the ape and man: an ever finer machine, with no extra ingredient.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Descartes 1637 · attacks premise 5

One can always tell that a machine is not a man by two signs. First, it could never put words together to answer the meaning of everything said in its presence, as even the dullest men can. Second, reason is a universal instrument, while each organ needs a particular arrangement for each action: it is impossible for a machine to have enough organs to act like reason in every situation of life. Parrots utter words, but without showing that they think what they say.

Mettrie replies
La Mettrie 1747 · La Mettrie's reply (without naming this passage)
He defies anyone to name a conclusive experiment against his plan: teaching a well-trained ape to speak, as the deaf-born are taught to speak. Given how much the ape's structure and operations resemble ours, he has very little doubt it would succeed. It would then be no longer a defective man, but a perfect man, with as much muscle as we have for thinking and profiting by his education.
The debate goes on (our summary) It is a bet, not a proof: La Mettrie never ran the experiment. Twentieth-century attempts to teach language to apes did not settle the question, since people still dispute whether the learned signs are real sentences or trained responses. Descartes's test is also still alive: it is the test applied to today's talking machines (our summary).
Descartes 1641 · attacks premise 3

There is a vast difference between mind and body: the body is always divisible, the mind is entirely indivisible. What thinks is therefore not a machine of parts.

Mettrie replies
La Mettrie 1747 · La Mettrie's reply (without naming Descartes)
If everything is explained by the structure of the brain, why divide the sensitive principle that thinks? For him this is a contradiction in the supporters of the simplicity of the mind: what is divided can no longer, without absurdity, be regarded as indivisible. He sees in the grand words (spirituality, immateriality) an abuse of language.
The debate goes on (our summary) The passage is short and does not directly answer Descartes's argument: it accuses dualists of themselves dividing thought into faculties, but a dualist can reply that it is the thinking subject, not its faculties, that is one. Diderot will give a more precise answer in 1769: there is no half of roundness (see Diderot's argument).
Leibniz (the mill) 1714 · attacks premise 3

Imagine a thinking machine, enlarged until one could walk into it as into a mill. One would find only parts pushing one another, and never anything to explain a perception. So the soul is not the working of a machine.

Mettrie replies
We have not yet found a direct reply by Mettrie in the texts.
Diderot 1769 · A materialist reply, but from Diderot (D'Alembert's Dream), not from La Mettrie
Diderot's character asks his opponent how he knows that sensitivity is incompatible with matter, when he knows the essence of neither. For him sensitivity is a property of matter, general or produced by organisation, and not a separate thing.
The debate goes on (our summary) Diderot does not solve the mill: he only says it cannot be decided, since we do not know what matter is. This echoes La Mettrie, who reproaches the spiritualists for defining a being whose nature is unknown; and the difficulty remains what is now called the hard problem of consciousness (our summary).
The debate goes on (our summary) La Mettrie did not answer the mill: he speaks of the monads, which he judges an unintelligible hypothesis, rather than of the thinking machine. He holds that we do not know what matter is, and that experience, not reason alone, must decide (our summary).
What today's voices say
Defend it
Robert SapolskyHe says humans and animals alike are biological machines, only more complicated, which is close to La Mettrie's idea.