QuestionsIs the mind the brain?The mill: perception is not a machine
Is the mind the brain?The mind is not matter

The mill: perception is not a machine

Gottfried Wilhelm Leibniz 1646 · 1716We live in the best of all possible worlds.
See profile
What it claims

Perception cannot be explained mechanically: it must be sought in the simple substance, not in the machine.

Why

If we walked inside an enlarged thinking machine, we would see only parts pushing each other, never a perception.

In short

"The mill: perception is not a machine" is an argument by Gottfried Wilhelm Leibniz (Monadology, 17) on the question "Is the mind the brain?" (answer: the mind is not matter). Its claim: Perception cannot be explained mechanically: it must be sought in the simple substance, not in the machine. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P2). AskPhilosophy presents 2 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

Monadology, 17
Valid with an implicit premise

Imagine a machine that thinks and feels, enlarged until you could walk into it as into a mill. What would you see? Parts pushing one another, never a perception. This 1714 thought experiment is often cited as the ancestor of today's debates about consciousness and the brain.

P1Explaining perception mechanically would mean explaining it by parts: their shapes and motions.
P2 · implicit premiseIf parts produced perception, we could in principle understand how by examining them, just as we understand a clock by looking at its gears.
P3Yet, walking inside the enlarged machine, we find only parts pushing one another, and never anything that explains a perception.
P4Perception lies either in a compound (a machine) or in a simple substance, without parts.
Therefore perception cannot be explained mechanically: it must be sought in the simple substance, not in the machine.

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 P2, the computer finds a case where perception really is produced by the parts, yet nothing shows when we examine them: the explanation exists, it is just invisible to the visitor.
Valid with P2. In the Monadology Leibniz does not write it down; he states it elsewhere as a general rule: when a thing has a quality, we must be able to conceive how that quality results from it. Without P2, perception could come from the parts without our seeing how. This is the point almost all modern critics aim at.
Analogy. Open a computer while it displays a photo: you will see only circuits and currents, the photo nowhere. For the computer, we can still explain how the image is produced. Leibniz thinks that for perception no explanation of this kind will ever be possible.

Objections

2

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

Locke 1690 · attacks premise 4

We do not know what thinking consists in. God, if he wishes, may well give a system of matter the faculty of thinking: this is no harder to conceive than joining a soul to it. So there is a third possibility: matter that thinks.

Leibniz replies
Leibniz
If God added thought to matter without placing a soul in it, it would be a sheer miracle: matter would receive a power it is naturally incapable of. In the natural order, we must be able to understand how a quality follows from its subject.
E
Emergence theories and neuroscience attacks premise 2

A property of the whole may be visible in none of the parts: we do not see life in a molecule, or liquidity in a drop of water observed atom by atom. Not seeing how the brain produces consciousness shows the limits of our current knowledge, not an impossibility.

no reply
summary: their text is not yet in our corpus
No reply possible: objection raised after the author's death (1716).
What today's voices say
Defend it
Donald HoffmanHe says Leibniz had the same idea in the Monadology: perceiving entities are more fundamental than the physical world, and neurons cannot create consciousness.