Philosophy 4610
Lecture Notes
Descartes: “The passions of the soul”
Last time, we considered Descartes’ argument for a real distinction between mind and
body. According to Descartes, the mind and the body are two different things; in fact,
they are two different kinds of things, defined by completely different attributes. For the
mind is defined, as we saw, by thinking and by the thoughts that it thinks. But body is
defined by the attribute of extension. For Descartes, the person is both body and mind,
both extended matter and thinking soul. But having shown that the body and the mind
are different and distinct, the problem Descartes now faces is the problem of getting them
back together. How does the mind connect with the body, and how does the body
connect with the mind?
It is clear that we need to say something about the relationship of the body and the mind,
on Descartes’ picture. As we have remarked, the mind is defined by its thoughts. But
there are two very general types of thoughts, and both seem to involve both the mind and
the body in some way. First, there are what Descartes calls actions. By “actions,”
Descartes means what we might call “volitions,” desires to do something, wants, and
intentions. Suppose I want an ice cream cone. Having this volition or action will cause
me to do something: in this case, to get up from my chair and walk to the ice cream shop.
Something will happen in the physical world – that is, my legs (physical bodies) will
move – because of something I thought. So we can think of actions, typically, as
thoughts in the mind or soul that cause something to happen in the body.
Again, there are the thoughts that Descartes calls “passions”, thoughts that are passive in
the sense that they just happen to us. This includes our perceptions or impressions of the
world around us. For instance, suppose I see the ice cream shop. There are light waves,
in the physical world, coming in to my physical eyes. But this is just a physical process,
until the signal reaches my mind. When the signal reaches my mind, I actually see the
ice cream shop: I am conscious of it and I have the thought that it is there. We can think
of passions, then, as typically thoughts in the mind or soul that are caused by something
happening in the body.
For Descartes, then, there must be causation both ways: things happening with the body
cause things to happen in the mind, and things happening in the mind cause things to
happen in the body. There is both physical to mental causation – as for instance when I
see the ice cream shop -- and mental to physical causation – as for instance when I go to
get an ice cream cone. Descartes accordingly faces the problem of how this works: how
do physical happenings and events in the body cause thoughts to occur, and how do
mental thoughts cause physical actions to occur? Descartes knew enough about anatomy
to know that nerve impulses from the nerves that run through our body – both the nerves
that perceive pain and sensation and the ones that cause motion -- terminate in the brain.
He thought, accordingly, that the place where the body “connects up” to the mind must
be in the brain somewhere. Even though the mind, being indissolvable, is in some sense
connected to the entire body, there must be – Descartes thought – a particular place at
which the two connect and at which the soul or mind acts particularly. Descartes chose
the pineal gland as this place, for a couple of reasons. First, it was one of the only parts
of the brain that had no obvious function that was known at Descartes’ time, so he
reasoned that it might well have the function of communicating with the non-physical
mind. Second, most parts of the brain are doubled (there are two cortical hemispheres,
for instance), but the pineal gland is single. So Descartes thought this must be the special
place, the “common sense” where mind and body affect one another.
This suggests the kind of story he tells at the end of the reading for today:
Thus, for example, if we see some animal approaching us, the light reflected from
its body forms two images, one in each of our eyes; and these images form two
others, by means of the optic nerves, on the internal surface of the brain facing its
cavities. Then, by means of the spirits that fill these cavities, the images radiate
toward the little gland which the spirits surround: the movement forming each
point of one of the images tends towards the same point on the gland as the
movement forming the corresponding point of the other image, which represents
the same part of the animal. In this way, the two images in the brain form only
one image on the gland, which acts directly upon the soul and makes it see the
shape of the animal ….
If, in addition, this shape is very strange and terrifying – that is, if it has a close
relation to things which have previously been harmful to the body – this arouses
the passion of anxiety in the soul, and then that of courage or perhaps fear and
terror, depending upon the particular temperament of the body or the strength of
the soul, and upon whether we have protected ourselves previously by defence or
by flight against the harmful things to which the present impression is related.
Thus in certain persons these factors dispose their brain in such a way that some
of the spirits reflected from the image formed on the gland proceed from there to
the nerves which serve to turn the back and move the legs in order to flee.” (p.
23)
The images produced by the animal in my eyes, turn into images in my brain. Somehow,
these two images come together, and they are channeled to the pineal gland. Now,
something else happens, something upon which everything turns. The images go from
being mere pictures to being experiences: somehow, as they enter the mind, I am
conscious of the animal, I understand and perceive it. Now, if I am also afrain of the
animal, my mind originates another thought: and this goes out from the pineal gland into
the body, causing the body to move to flee. Both the mind and the body have been
involved, together, in causing my reaction. Without both working together, we would not
be able to live in the world as we indeed can.
This dualist picture of the mind and brain might seem to be attractive in many ways. We
saw how it followed from Descartes’ starting point of doubting everything, and finding
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that the certainty of the “I” as a thinking thing is the only point from which we can start.
It offers the hope of explaining what otherwise would be a deep mystery: how anything
like consciousness or intelligence can occur in a world that otherwise seems devoid of it.
But there are also lots of problems with the dualist view, and we can see some of these
problems by reflecting on the story it tells about causality.
To see some of these problems, consider the following principle
Causal closure of the physical: Every physical event that occurs is completely explained
by other physical events.
This principle is quite plausible. Suppose I throw a rock through the window. Now:
why did the window break? It broke because of the rock, flying towards it. This
completely explains why it broke. It seems obvious that every physical event that occurs
in the world is caused by another physical event. Physical events occur, after all, in
accordance with the laws of physics, laws that are strict and have no exceptions. It seems
that if a physical event ever occurred that could not be explained by other physical
events, this would have to be a kind of miracle: something that does not follow the laws
of physics that otherwise hold everywhere.
But now consider the example we consdired before: my going to get an ice cream cone.
Surely, this is a physical event. It involves physical matter, in particular my legs, moving
in a particular kind of way. And as Descartes himself admits, this is caused to happen by
other physical events: by the nerve impulses that cause my muscles to contract, etc. In
fact, we now understand a great deal more about the causation of this kind of action than
Descartes did. We know the impulses that lead my legs to move come from my brain,
and we know roughly what area they come from and how they originate in electrical
impulses. These electrical impulses are themselves caused by other electrical impulses,
which ultimately are caused by perceptions of my sense organs. We know, at least in
outline, how this entire story goes. But this entire story of nerves and electrical impulses
is a physical story. It never refers to, or needs to refer to, something that is not physical.
If this physical story is true, then everything about my going to get an ice cream cone can
indeed be explained completely by other physical events. There is no need to postulate
non-physical mind which is causing this to happen.
The problem, then, is that the Cartesian dualist, in order to defend his theory, must deny
the causal closure of the physical. He must think that there are physical events – such
as my legs moving to go toward the ice cream shop – that cannot be explained in terms of
other physical events that cause them. Instead, for the Cartesian dualist, these events
must ultimately have to be explained by non-physical events, things that happen in the
non-physical mind. So if the Cartesian dualist is right, then the causal closure of the
physical is false. There are some events that cannot be explained in physical terms, no
matter how much we find out. So the Cartesian dualist must not only deny that any
particular physical explanation we give is correct, but he must deny that there is any
possible physical explanation at all. No matter how much we find out, scientifically,
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about the brain and the body, no matter how fully we understand the sequence of causes
that leads from physical perception to physical action, this story will leave something out.
Another possibility for the Cartesian dualist might be to agree with the causal closure of
the physical. Every event, including actions, can be explained in physical terms: but the
mind still exists and is distinct from the body. This is the position known as epiphenomenalism: on which there is causation from the body and brain to the mind (for
instance when we perceive or are conscious of something), but not causation from the
mind to the body. Someone who holds epiphenomenalism can indeed agree that all
physical events, including actions, have a physical explanation: but he thinks that the
mind exists as well, and has various thoughts and perceptions.
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