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preliminaries, she dives into the problems she has with Descartes’s mind/
08
body dualism. Her writing is urgent and pointed:
09
10
How can the soul of a man determine the spirits of his body
11
so as to produce voluntary actions (given that the soul is only a
12
thinking substance)? For it seems that all determination of
13
movement is made by the pushing of a thing moved, either that
14
it is pushed by the thing which moves it or it is affected by the
15
quality or shape of the surface of that thing. For the first two
16
conditions, touching is necessary, for the third extension. For
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touching, you exclude entirely the notion that you have of the
18
soul; extension seems to me incompatible with an immaterial
19
thing. This is why I ask you to give a definition of the soul more
20
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
23
mind and body act on each other, fine. But how, exactly? What precisely
24
happens?
25
It’s not simply a matter of “We don’t know this part of the story, but
26
we’ll figure it out eventually.” Elisabeth was presumably not a physicalist,
27
someone who believes that the world is made purely of physical stuff. Not
28
many people were in 1643. She was a pious Christian, and most likely had
29
no trouble believing there was more to life than the immediately apparent
30
world. But she was also scrupulously honest, and could not understand how
31
an immaterial mind was supposed to push around the material body. When
32
something pushes something else, the two things need to be located at the
33
same place. But the mind isn’t “located” anywhere— it’s not part of the
34
physical plane. Your mind has a thought, such as “I’ve got it— Cogito, ergo
S35
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-
02
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
05
somewhat patronizing. He wanted to remain in the princess’s favor, but at
06
first he didn’t take her question all that seriously, offering a halfhearted
07
suggestion that “mind” was somewhat like “heaviness,” though not really.
08
His argument was the following (roughly paraphrased):
09
10
• We want to know how an immaterial substance such as the
11
soul can influence the motion of a physical object like the
12
body.
13
• Well, “heaviness” is an immaterial quality, not a physical ob-
14
ject itself. And yet we often speak as if it has an effect on what
15
happens to physical objects—“I couldn’t lift that package
16
because it was too heavy.” That is, we attribute causal pow-
17
ers to it.
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• Of course, he quickly notes, mind is not exactly like that,
19
because mind actually is a separate kind of substance. Never-
20
theless, perhaps the way the mind influences the body is
21
somehow analogous to the way we say heaviness influences
22
objects, even though one is a true substance and the other
23
is not.
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25
If you’re confused, you should be, since Descartes’s story makes no sense.
26
Ironically, though, it’s close to correct. To a poetic naturalist, “mind” is
27
simply a way of talking about the behavior of certain collections of physical
28
matter, just as “heaviness” is. The problem is that Descartes is nobody’s
29
naturalist. His burden was to explain how something nonphysical could
30
influence something physical, and he proffered an explanation that utterly
31
failed to do so.
32
Elisabeth was not impressed. In her subsequent letters she continued to
33
press him on the issue, explaining that she knew perfectly well what heavi-
34
ness was, but couldn’t fathom how it was supposed to help her understand
35S
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-
01
soning.
02
Descartes never offered a satisfactory answer. He believed that the
03
mind’s relationship to the body was not like that of a captain to his ship,
04
with the mind pushing around the material object; rather, the two were
05
“tightly joined” and “mingled together.” And that mingling occurred, he
06
hypothesized, in a very particular anatomical location: the pineal gland, a
07
tiny part of the vertebrate brain that (we now know) produces the hormone
08
melatonin, responsible for our sleep rhythms. He focused on that specific
09
organ because it seemed to be the only part of the human brain that was
10
unified rather than split bicamerally, and he believed that the mind only
11
experienced one thought at a time. Descartes suggested that the pineal
12
gland was a physical object that could be moved both by the “animal spirits”
13
of the body, and by the immaterial soul itself, serving to mediate influences
14
between the two.
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25
26
An illustration of the role of the pineal gland,
27
from Descartes’s Treatise of Man. (Illustration
28
by René Descartes)
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30
The suggestion that the pineal gland se
rves as “principal seat of the soul”
31
never really caught on, even among thinkers who were otherwise sympa-
32
thetic to Cartesian dualism. People continued to try to understand how the
33
mind and body could interact. Nicolas Malebranche, a French philosopher
34
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.
02
As Isaac Newton later noted in a discussion of vision, “To determine by
03
what modes or actions light produceth in our minds the phantasm of co-
04
lour is not so easie.”
05
•
06
07
How an immaterial soul might interact with the physical body remains a
08
challenging question for dualists even today, and indeed it has grown enor-
09
mously more difficult to see how it might be addressed. While Elisabeth
10
pointed out some of the difficulties with the idea, she didn’t offer an incon-
11
trovertible argument that souls and bodies cannot interact in any possible
12
way. She simply noted a crucial difficulty with the dualistic worldview: it’s
13
hard to see how something immaterial could affect the motion of some-
14
thing material. Religious believers will sometimes point to an aspect of
15
naturalism that hasn’t yet been fully explicated, such as the origin of the
16
universe or the nature of consciousness, and insist that naturalism is there-
17
fore defeated; such arguments are rightly derided as “God of the gaps” rea-
18
soning, finding evidence for the divine in the gaps in our physical
19
understanding. Likewise, the inability of Descartes and his successors to
20
explain how souls and bodies interact doesn’t undermine dualism once and
21
for all; to pretend otherwise would be indulging in “naturalism of the gaps.”
22
It does highlight the difficulties that dualism must face. Today, those
23
difficulties are larger than anything Descartes would have imagined. Mod-
24
ern science knows a lot more about the behavior of matter than seventeenth-
25
century science did. The Core Theory of contemporary physics describes
26
the atoms and forces that constitute our brains and bodies in exquisite de-
27
tail, in terms of a rigid and unforgiving set of formal equations that leaves
28
no wiggle room for intervention by nonmaterial influences. The way we
29
talk about immaterial souls, meanwhile, has not risen to that level of so-
30
phistication. To imagine that the soul pushes around the electrons and pro-
31
tons and neutrons in our bodies in a way that we haven’t yet detected is
32
certainly conceivable, but it implies that modern physics is profoundly
33
wrong in a way that has so far eluded every controlled experiment ever per-
34
formed. How should we modify the Core Theory equation (shown in the
35S
Appendix) to allow for the soul to influence the particles in our body? It’s
36N
a substantial hurdle to leap.
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For the moment, Elisabeth’s questions remain unanswered. Twentieth-
01
century British philosopher Gilbert Ryle criticized what he called “the
02
dogma of the Ghost in the Machine.” As Ryle saw it, thinking of the mind
03
as a separate kind of thing from the body was one big mistake, not just in
04
how the mind works but in what it fundamentally is. We certainly don’t
05
have a comprehensive understanding of how matter in motion gives rise to
06
thought and feeling. But from what we do understand, that seems like a
07
much simpler task than making sense of how the mind could be a com-
08
pletely distinct category of existence.
09
Another strategy for the would-be dualist is to give up on straightfor-
10
ward Cartesian “substance dualism,” in which mind and matter are two
11
distinct substances, and go for something more subtle. Property dualism is
12
the idea that there’s only one kind of stuff— matter— but it has both phys-
13
ical properties and mental properties. We can imagine how Princess Elisa-
14
beth might have reacted to this idea: “So how do the mental properties
15
affect the physical ones?” We’ll tackle this question in greater depth, but it’s
16
not hard to see how the move to property dualism merely pushes the issue
17
back a step rather than actually resolving it.
18
19
•
20
Besides her insistent questioning on the mind/ body interaction question,
21
Elisabeth had a profound influence on Descartes’s later work. They corre-
22
sponded about technical scientific issues, as this paragraph of hers demon-
23
strates:
24
25
I believe that you will justly retract the opinion you have of
26
my understanding once you find out that I do not understand
27
how quicksilver is formed, both so full of agitation and so heavy,
28
contrary to the definition you have given of heaviness. And also
29
when the body E, in the figure on page 255, presses it when it is
30
above, why does it resist this contrary force when it is below, any
31
more than air does in leaving a ship which it has been pressing?
32
33
Most importantly, she forcefully argued to Descartes that he was too
34
aloof and disinterested in his moral and ethical philosophy, and needed to
S35
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
02
Elisabeth, was entitled The Passions of the Soul, and can be thought of as a
03
response to her prompting.
04
Elisabeth wa
s a devoted Christian of the late Reformation, not a
05
modern- day naturalist. It is her attitudes and methodology, not her beliefs,
06
that make her a hero for this book. She was not content to posit an attrac-
07
tive picture of the world, such as mind/ body dualism, and move on from
08
there without further questioning. How would it work? How does this
09
move that? How would we know? Good questions to be asking, no matter
10
how you ultimately view the fundamental nature of reality.
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14
15
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20
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04
Death Is the End
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08
09
10
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12
O
13
ne of the most impressive properties of the Core Theory of the
14
physics underlying everyday life is its rigidity. We specify a par-
15
ticular physical situation, such as a configuration of atoms and
16
ions in a neuron in your brain, and the theory predicts with magnificent
17
accuracy how that situation will evolve. At the microscopic scale, quantum
18
mechanics implies that individual measurement outcomes are expressed in
19
probabilities rather than certainties, but those probabilities are unambigu-
20
ously fixed by the theory, and when we aggregate many particles the overall
21
behavior becomes fantastically predictable (at least in principle, to a La-
22
place’s Demon– level intellect). There are no vague or unspecified pieces
23
waiting to be filled in; the equations predict how matter and energy behave
24
in any given situation, whether it’s the Earth revolving around the sun, or
25
electrochemical impulses cascading through your central nervous system.
26
This rigidity makes the modern version of Princess Elisabeth’s question
27
enormously more pressing than it had been in the seventeenth century.
28
Whether you are a physicalist who believes that there is nothing to us other
29
than the particles of the Core Theory, or someone who thinks that there is
The Big Picture Page 37