Leibniz and the Machine

Can we explain the existence of an individual’s mind by looking at the workings of their brain? An influential argument in the philosophy of mind was put forth by Gottfried Wilhelm Leibniz, in his work The Monadology, in which he argues that the mind is not something which is natural to physical matter:

Moreover, we must confess that perception, and what depends on it, is inexplicable in terms of mechanical reasons, that is, through shapes and motions. If we imagine that there is a machine whose structure makes it think, sense, and have perceptions, we could conceive it enlarged, keeping the same proportions, so that we could enter into it, as one enters into a mill. Assuming that, when inspecting its interior, we will only find parts that push one another, and we will never find anything to explain a perception. And so, we should seek perception in the simple substance and not in the composite or in the machine.

This argument against materialism––the claim that everything is material, including mental states––first appears in section 17 of The Monadology. Leibniz seems to be making the following argument: on entering the enlarged machine, a visitor would only see parts interacting with one-another, like cogs in a watch. But no perceptions or thoughts would be visible to the spectator upon inspecting the machine; only the interactions of the machine parts themselves would be visible. Thought or perception cannot be deduced from the amalgamation of the working and moving parts of the machine. Nothing like a mind would be visible to the visitor––that within the mechanical movements of the machine, thought and perception is taking place. So, the argument goes, matter could not possibly give rise to the mind.

In his New Essays on Human Understanding, Leibniz offers a further passage that seems to highlight the importance of reason or intelligibility:

As for thought, it is certain, as our author more than once acknowledges, that it cannot be an intelligible modification of matter and be comprehensible and explicable in terms of it. That is, a sentient or thinking being is not a mechanical thing like a watch or a mill: one cannot conceive of sizes and shapes and motions combining mechanically to produce something which thinks, and senses too, in a mass where [formerly] there was nothing of the kind – something which would likewise be extinguished by the machine’s going out of order. So sense and thought are not something which is natural to matter.

The claim that “one cannot conceive of sizes and shapes and motions combining mechanically to produce something which thinks, and senses too, in a mass where [formerly] there was nothing of the kind” highlights the profound problem of the unity of perception. If it is indeed the case, as we currently believe, that the mind is a production of the brain, how is it that biological parts working together are able to produce the unified self––the “I”? In my opinion, I do not believe that Leibniz has sufficiently shown that matter cannot produce thought––because reasons of inconceivability are not enough (on the basis that just because we cannot imagine something does not render it false). However, Leibniz was aware of this issue:

It is no proof of the impossibility of something merely to say that one cannot conceive this or that, when one doesn’t make clear where it conflicts with reason, and when the difficulty is only one of imagination, and not of understanding.

Overall, I think Leibniz’ claim is that a machine with parts being capable of thought and perception is something that clashes with reason––that we have no positive reason to believe that a unity of a self could arise from interacting material parts. However, the literature on Leibniz’ claim is fairly split: there are interpretations where it is argued that the main aim of Leibniz’s argument in section 17 of the Monadology is to highlight that mechanical explanation cannot account for the unity of the self––that we experience ourselves as one thing (see Margaret Wilson, Ideas and Mechanisms 1999). Whereas philosophers John Searle, Thomas Nagel, Colin McGinn, Frank Jackson, etc., have taken Leibniz at face value, and are of the opinion that thought and sensation will elude capture by material or physical theories of the mind.