The Big Picture
Page 37
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preliminaries, she dives into the problems she has with Descartes’s mind/
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body dualism. Her writing is urgent and pointed:
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How can the soul of a man determine the spirits of his body
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so as to produce voluntary actions (given that the soul is only a
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thinking substance)? For it seems that all determination of
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movement is made by the pushing of a thing moved, either that
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it is pushed by the thing which moves it or it is affected by the
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quality or shape of the surface of that thing. For the first two
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conditions, touching is necessary, for the third extension. For
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touching, you exclude entirely the notion that you have of the
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soul; extension seems to me incompatible with an immaterial
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thing. This is why I ask you to give a definition of the soul more
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specific than the one you gave in your Metaphysics.
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It’s a question that cuts to the heart of the mind/ body split. You say that
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mind and body act on each other, fine. But how, exactly? What precisely
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happens?
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It’s not simply a matter of “We don’t know this part of the story, but
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we’ll figure it out eventually.” Elisabeth was presumably not a physicalist,
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someone who believes that the world is made purely of physical stuff. Not
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many people were in 1643. She was a pious Christian, and most likely had
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no trouble believing there was more to life than the immediately apparent
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world. But she was also scrupulously honest, and could not understand how
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an immaterial mind was supposed to push around the material body. When
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something pushes something else, the two things need to be located at the
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same place. But the mind isn’t “located” anywhere— it’s not part of the
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physical plane. Your mind has a thought, such as “I’ve got it— Cogito, ergo
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sum. ” How is that thought supposed to lead to the body lifting a pen and
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committing those words to paper? How is it even conceivable that some-
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thing with no extent or location could influence an ordinary physical
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object?
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Descartes’s initial response was at once both fulsomely flattering and
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somewhat patronizing. He wanted to remain in the princess’s favor, but at
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first he didn’t take her question all that seriously, offering a halfhearted
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suggestion that “mind” was somewhat like “heaviness,” though not really.
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His argument was the following (roughly paraphrased):
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• We want to know how an immaterial substance such as the
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soul can influence the motion of a physical object like the
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body.
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• Well, “heaviness” is an immaterial quality, not a physical ob-
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ject itself. And yet we often speak as if it has an effect on what
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happens to physical objects—“I couldn’t lift that package
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because it was too heavy.” That is, we attribute causal pow-
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ers to it.
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• Of course, he quickly notes, mind is not exactly like that,
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because mind actually is a separate kind of substance. Never-
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theless, perhaps the way the mind influences the body is
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somehow analogous to the way we say heaviness influences
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objects, even though one is a true substance and the other
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is not.
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If you’re confused, you should be, since Descartes’s story makes no sense.
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Ironically, though, it’s close to correct. To a poetic naturalist, “mind” is
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simply a way of talking about the behavior of certain collections of physical
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matter, just as “heaviness” is. The problem is that Descartes is nobody’s
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naturalist. His burden was to explain how something nonphysical could
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influence something physical, and he proffered an explanation that utterly
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failed to do so.
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Elisabeth was not impressed. In her subsequent letters she continued to
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press him on the issue, explaining that she knew perfectly well what heavi-
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ness was, but couldn’t fathom how it was supposed to help her understand
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the interactions of physical bodies and immaterial minds. She asks why a
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mind that is completely independent of the body could be so affected by
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it— why, for example, “the vapors” are able to affect our capacity for rea-
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soning.
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Descartes never offered a satisfactory answer. He believed that the
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mind’s relationship to the body was not like that of a captain to his ship,
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with the mind pushing around the material object; rather, the two were
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“tightly joined” and “mingled together.” And that mingling occurred, he
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hypothesized, in a very particular anatomical location: the pineal gland, a
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tiny part of the vertebrate brain that (we now know) produces the hormone
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melatonin, responsible for our sleep rhythms. He focused on that specific
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organ because it seemed to be the only part of the human brain that was
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unified rather than split bicamerally, and he believed that the mind only
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experienced one thought at a time. Descartes suggested that the pineal
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gland was a physical object that could be moved both by the “animal spirits”
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of the body, and by the immaterial soul itself, serving to mediate influences
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between the two.
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An illustration of the role of the pineal gland,
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from Descartes’s Treatise of Man. (Illustration
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by René Descartes)
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The suggestion that the pineal gland se
rves as “principal seat of the soul”
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never really caught on, even among thinkers who were otherwise sympa-
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thetic to Cartesian dualism. People continued to try to understand how the
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mind and body could interact. Nicolas Malebranche, a French philosopher
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who was born just a few years before Elisabeth and Descartes began their
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correspondence, suggested that God was the only causal agent in the world,
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and that every mind/ brain interaction was mediated by God’s intervention.
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As Isaac Newton later noted in a discussion of vision, “To determine by
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what modes or actions light produceth in our minds the phantasm of co-
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lour is not so easie.”
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How an immaterial soul might interact with the physical body remains a
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challenging question for dualists even today, and indeed it has grown enor-
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mously more difficult to see how it might be addressed. While Elisabeth
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pointed out some of the difficulties with the idea, she didn’t offer an incon-
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trovertible argument that souls and bodies cannot interact in any possible
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way. She simply noted a crucial difficulty with the dualistic worldview: it’s
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hard to see how something immaterial could affect the motion of some-
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thing material. Religious believers will sometimes point to an aspect of
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naturalism that hasn’t yet been fully explicated, such as the origin of the
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universe or the nature of consciousness, and insist that naturalism is there-
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fore defeated; such arguments are rightly derided as “God of the gaps” rea-
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soning, finding evidence for the divine in the gaps in our physical
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understanding. Likewise, the inability of Descartes and his successors to
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explain how souls and bodies interact doesn’t undermine dualism once and
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for all; to pretend otherwise would be indulging in “naturalism of the gaps.”
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It does highlight the difficulties that dualism must face. Today, those
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difficulties are larger than anything Descartes would have imagined. Mod-
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ern science knows a lot more about the behavior of matter than seventeenth-
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century science did. The Core Theory of contemporary physics describes
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the atoms and forces that constitute our brains and bodies in exquisite de-
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tail, in terms of a rigid and unforgiving set of formal equations that leaves
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no wiggle room for intervention by nonmaterial influences. The way we
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talk about immaterial souls, meanwhile, has not risen to that level of so-
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phistication. To imagine that the soul pushes around the electrons and pro-
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tons and neutrons in our bodies in a way that we haven’t yet detected is
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certainly conceivable, but it implies that modern physics is profoundly
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wrong in a way that has so far eluded every controlled experiment ever per-
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formed. How should we modify the Core Theory equation (shown in the
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Appendix) to allow for the soul to influence the particles in our body? It’s
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a substantial hurdle to leap.
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For the moment, Elisabeth’s questions remain unanswered. Twentieth-
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century British philosopher Gilbert Ryle criticized what he called “the
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dogma of the Ghost in the Machine.” As Ryle saw it, thinking of the mind
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as a separate kind of thing from the body was one big mistake, not just in
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how the mind works but in what it fundamentally is. We certainly don’t
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have a comprehensive understanding of how matter in motion gives rise to
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thought and feeling. But from what we do understand, that seems like a
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much simpler task than making sense of how the mind could be a com-
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pletely distinct category of existence.
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Another strategy for the would-be dualist is to give up on straightfor-
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ward Cartesian “substance dualism,” in which mind and matter are two
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distinct substances, and go for something more subtle. Property dualism is
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the idea that there’s only one kind of stuff— matter— but it has both phys-
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ical properties and mental properties. We can imagine how Princess Elisa-
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beth might have reacted to this idea: “So how do the mental properties
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affect the physical ones?” We’ll tackle this question in greater depth, but it’s
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not hard to see how the move to property dualism merely pushes the issue
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back a step rather than actually resolving it.
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Besides her insistent questioning on the mind/ body interaction question,
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Elisabeth had a profound influence on Descartes’s later work. They corre-
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sponded about technical scientific issues, as this paragraph of hers demon-
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strates:
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I believe that you will justly retract the opinion you have of
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my understanding once you find out that I do not understand
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how quicksilver is formed, both so full of agitation and so heavy,
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contrary to the definition you have given of heaviness. And also
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when the body E, in the figure on page 255, presses it when it is
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above, why does it resist this contrary force when it is below, any
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more than air does in leaving a ship which it has been pressing?
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Most importantly, she forcefully argued to Descartes that he was too
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aloof and disinterested in his moral and ethical philosophy, and needed to
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take greater account of everyday human reality and “the passions” (what we
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might today think of as “emotions”). His last published work, dedicated to
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Elisabeth, was entitled The Passions of the Soul, and can be thought of as a
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response to her prompting.
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Elisabeth wa
s a devoted Christian of the late Reformation, not a
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modern- day naturalist. It is her attitudes and methodology, not her beliefs,
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that make her a hero for this book. She was not content to posit an attrac-
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tive picture of the world, such as mind/ body dualism, and move on from
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there without further questioning. How would it work? How does this
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move that? How would we know? Good questions to be asking, no matter
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how you ultimately view the fundamental nature of reality.
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Death Is the End
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ne of the most impressive properties of the Core Theory of the
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physics underlying everyday life is its rigidity. We specify a par-
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ticular physical situation, such as a configuration of atoms and
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ions in a neuron in your brain, and the theory predicts with magnificent
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accuracy how that situation will evolve. At the microscopic scale, quantum
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mechanics implies that individual measurement outcomes are expressed in
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probabilities rather than certainties, but those probabilities are unambigu-
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ously fixed by the theory, and when we aggregate many particles the overall
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behavior becomes fantastically predictable (at least in principle, to a La-
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place’s Demon– level intellect). There are no vague or unspecified pieces
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waiting to be filled in; the equations predict how matter and energy behave
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in any given situation, whether it’s the Earth revolving around the sun, or
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electrochemical impulses cascading through your central nervous system.
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This rigidity makes the modern version of Princess Elisabeth’s question
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enormously more pressing than it had been in the seventeenth century.
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Whether you are a physicalist who believes that there is nothing to us other
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than the particles of the Core Theory, or someone who thinks that there is