philosophy is his thesis that mind and body are really distinct–a
thesis now called "mind-body dualism." He reaches this conclusion by
arguing that the nature of the mind (that is, a thinking, non-extended
thing) is completely different from that of the body (that is, an
extended, non-thinking thing), and therefore it is possible for one to
exist without the other. This argument gives rise to the famous
problem of mind-body causal interaction still debated today: how can
the mind cause some of our bodily limbs to move (for example, raising
one's hand to ask a question), and how can the body's sense organs
cause sensations in the mind when their natures are completely
different? This article examines these issues as well as Descartes'
own response to this problem through his brief remarks on how the mind
is united with the body to form a human being. This will show how
these issues arise because of a misconception about Descartes' theory
of mind-body union, and how the correct conception of their union
avoids this version of the problem. The article begins with an
examination of the term "real distinction" and of Descartes' probable
motivations for maintaining his dualist thesis.
1. What is a Real Distinction?
It is important to note that for Descartes "real distinction" is a
technical term denoting the distinction between two or more substances
(see Principles, part I, section 60). A substance is something that
does not require any other creature to exist—it can exist with only
the help of God's concurrence—whereas, a mode is a quality or
affection of that substance (see Principles part I, section 5).
Accordingly, a mode requires a substance to exist and not just the
concurrence of God. Being sphere shaped is a mode of an extended
substance. For example, a sphere requires an object extended in three
dimensions in order to exist: an unextended sphere cannot be conceived
without contradiction. But a substance can be understood to exist
alone without requiring any other creature to exist. For example, a
stone can exist all by itself. That is, its existence is not dependent
upon the existence of minds or other bodies; and, a stone can exist
without being any particular size or shape. This indicates for
Descartes that God, if he chose, could create a world constituted by
this stone all by itself, showing further that it is a substance
"really distinct" from everything else except God. Hence, the thesis
that mind and body are really distinct just means that each could
exist all by itself without any other creature, including each other,
if God chose to do it. However, this does not mean that these
substances do exist separately. Whether or not they actually exist
apart is another issue entirely.
2. Why a Real Distinction?
A question one might ask is: what's the point of arguing that mind and
body could each exist without the other? What's the payoff for going
through all the trouble and enduring all the problems to which it
gives rise? For Descartes the payoff is twofold. The first is
religious in nature in that it provides a rational basis for a hope in
the soul's immortality [because Descartes presumes that the mind and
soul are more or less the same thing]. The second is more
scientifically oriented, for the complete absence of mentality from
the nature of physical things is central to making way for Descartes'
version of the new, mechanistic physics. This section investigates
both of these motivating factors.
a. The Religious Motivation
In his Letter to the Sorbonne published at the beginning of his
seminal work, Meditations on First Philosophy, Descartes states that
his purpose in showing that the human mind or soul is really distinct
from the body is to refute those "irreligious people" who only have
faith in mathematics and will not believe in the soul's immortality
without a mathematical demonstration of it. Descartes goes on to
explain how, because of this, these people will not pursue moral
virtue without the prospect of an afterlife with rewards for virtue
and punishments for vice. But, since all the arguments in the
Meditations—including the real distinction arguments— are for
Descartes absolutely certain on a par with geometrical demonstrations,
he believes that these people will be obliged to accept them. Hence,
irreligious people will be forced to believe in the prospect of an
afterlife. However, recall that Descartes' conclusion is only that the
mind or soul can exist without the body. He stops short of
demonstrating that the soul is actually immortal. Indeed, in the
Synopsis to the Mediations, Descartes claims only to have shown that
the decay of the body does not logically or metaphysically imply the
destruction of the mind: further argumentation is required for the
conclusion that the mind actually survives the body's destruction.
This would involve both "an account of the whole of physics" and an
argument showing that God cannot annihilate the mind. Yet, even though
the real distinction argument does not go this far, it does, according
to Descartes, provide a sufficient foundation for religion, since the
hope for an afterlife now has a rational basis and is no longer a mere
article of faith.
b. The Scientific Motivation
The other motive for arguing that mind and body could each exist
without the other is more scientifically oriented, stemming from
Descartes' intended replacement of final causal explanations in
physics thought to be favored by late scholastic-Aristotelian
philosophers with mechanistic explanations based on the model of
geometry. Although the credit for setting the stage for this
scholastic-Aristotelian philosophy dominant at Descartes' time should
go to Thomas Aquinas (because of his initial, thorough interpretation
and appropriation of Aristotle's philosophy), it is also important to
bear in mind that other thinkers working within this Aristotelian
framework such as Duns Scotus, William of Ockham, and Francisco
Suarez, diverged from the Thomistic position on a variety of important
issues. Indeed, by Descartes' time, scholastic positions divergent
from Thomism became so widespread and subtle in their differences that
sorting them out was quite difficult. Notwithstanding this convoluted
array of positions, Descartes understood one thesis to stand at the
heart of the entire tradition: the doctrine that everything ultimately
behaved for the sake of some end or goal. Though these "final causes,"
as they were called, were not the only sorts of causes recognized by
scholastic thinkers, it is sufficient for present purposes to
recognize that Descartes believed scholastic natural philosophers used
them as principles for physical explanations. For this reason, a brief
look at how final causes were supposed to work is in order.
Descartes understood all scholastics to maintain that everything was
thought to have a final cause that is the ultimate end or goal for the
sake of which the rest of the organism was organized. This principle
of organization became known as a thing's "substantial form," because
it was this principle that explained why some hunk of matter was
arranged in such and such a way so as to be some species of substance.
For example, in the case of a bird, say, the swallow, the substantial
form of swallowness was thought to organize matter for the sake of
being a swallow species of substance. Accordingly, any dispositions a
swallow might have, such as the disposition for making nests, would
then also be explained by means of this ultimate goal of being a
swallow; that is, swallows are disposed for making nests for the sake
of being a swallow species of substance. This explanatory scheme was
also thought to work for plants and inanimate natural objects.
A criticism of the traditional employment of substantial forms and
their concomitant final causes in physics is found in the Sixth
Replies where Descartes examines how the quality of gravity was used
to explain a body's downward motion:
But what makes it especially clear that my idea of gravity was
taken largely from the idea I had of the mind is the fact that I
thought that gravity carried bodies toward the centre of the earth as
if it had some knowledge of the centre within itself (AT VII 442: CSM
II 298).
On this pre-Newtonian account, a characteristic goal of all bodies was
to reach its proper place, namely, the center of the earth. So, the
answer to the question, "Why do stones fall downward?" would be,
"Because they are striving to achieve their goal of reaching the
center of the earth." According to Descartes, this implies that the
stone must have knowledge of this goal, know the means to attain it,
and know where the center of the earth is located. But, how can a
stone know anything? Surely only minds can have knowledge. Yet, since
stones are inanimate bodies without minds, it follows that they cannot
know anything at all—let alone anything about the center of the earth.
Descartes continues on to make the following point:
But later on I made the observations which led me to make a
careful distinction between the idea of the mind and the ideas of body
and corporeal motion; and I found that all those other ideas of . . .
'substantial forms' which I had previously held were ones which I had
put together or constructed from those basic ideas (AT VII 442-3: CSM
II 298).
Here, Descartes is claiming that the concept of a substantial form as
part of the entirely physical world stems from a confusion of the
ideas of mind and body. This confusion led people to mistakenly
ascribe mental properties like knowledge to entirely non-mental things
like stones, plants, and, yes, even non-human animals. The real
distinction of mind and body can then also be used to alleviate this
confusion and its resultant mistakes by showing that bodies exist and
move as they do without mentality, and as such principles of mental
causation such as goals, purposes (that is, final causes), and
knowledge have no role to play in the explanation of physical
phenomena. So the real distinction of mind and body also serves the
more scientifically oriented end of eliminating any element of
mentality from the idea of body. In this way, a clear understanding of
the geometrical nature of bodies can be achieved and better
explanations obtained.
3. The Real Distinction Argument
Descartes formulates this argument in many different ways, which has
led many scholars to believe there are several different real
distinction arguments. However, it is more accurate to consider these
formulations as different versions of one and the same argument. The
fundamental premise of each is identical: each has the fundamental
premise that the natures of mind and body are completely different
from one another.
The First Version
The first version is found in this excerpt from the Sixth Meditation:
[O]n the one hand I have a clear and distinct idea of myself, in
so far as I am simply a thinking, non-extended thing [that is, a
mind], and on the other hand I have a distinct idea of body, in so far
as this is simply an extended, non-thinking thing. And accordingly, it
is certain that I am really distinct from my body, and can exist
without it (AT VII 78: CSM II 54).
Notice that the argument is given from the first person perspective
(as are the entire Meditations). This "I" is, of course, Descartes
insofar as he is a thinking thing or mind, and the argument is
intended to work for any "I" or mind. So, for present purposes, it is
safe to generalize the argument by replacing "I" with "mind" in the
relevant places:
1. I have a clear and distinct idea of the mind as a thinking,
non-extended thing.
2. I have a clear and distinct idea of body as an extended,
non-thinking thing.
3. Therefore, the mind is really distinct from the body and can
exist without it.
At first glance it may seem that, without justification, Descartes is
bluntly asserting that he conceives of mind and body as two completely
different things, and that from his conception, he is inferring that
he (or any mind) can exist without the body. But this is no blunt,
unjustified assertion. Much more is at work here: most notably what is
at work is his doctrine of clear and distinct ideas and their
veridical guarantee. Indeed the truth of his intellectual perception
of the natures of mind and body is supposed to be guaranteed by the
fact that this perception is "clear and distinct." Since the
justification for these two premises rests squarely on the veridical
guarantee of whatever is "clearly and distinctly" perceived, a brief
side trip explaining this doctrine is in order.
Descartes explains what he means by a "clear and distinct idea" in his
work Principles of Philosophy at part I, section 45. Here he likens a
clear intellectual perception to a clear visual perception. So, just
as someone might have a sharply focused visual perception of
something, an idea is clear when it is in sharp intellectual focus.
Moreover, an idea is distinct when, in addition to being clear, all
other ideas not belonging to it are completely excluded from it.
Hence, Descartes is claiming in both premises that his idea of the
mind and his idea of the body exclude all other ideas that do not
belong to them, including each other, and all that remains is what can
be clearly understood of each. As a result, he clearly and distinctly
understands the mind all by itself, separately from the body, and the
body all by itself, separately from the mind.
According to Descartes, his ability to clearly and distinctly
understand them separately from one another implies that each can
exist alone without the other. This is because "[e]xistence is
contained in the idea or concept of every single thing, since we
cannot conceive of anything except as existing. Possible or contingent
existence is contained in the concept of a limited thing…" (AT VII
166: CSM II 117). Descartes, then, clearly and distinctly perceives
the mind as possibly existing all by itself, and the body as possibly
existing all by itself. But couldn't Descartes somehow be mistaken
about his clear and distinct ideas? Given the existence of so many
non-thinking bodies like stones, there is no question that bodies can
exist without minds. So, even if he could be mistaken about what he
clearly and distinctly understands, there is other evidence in support
of premise 2. But can minds exist without bodies? Can thinking occur
without a brain? If the answer to this question is "no," the first
premise would be false and, therefore, Descartes would be mistaken
about one of his clear and distinct perceptions. Indeed, since we have
no experience of minds actually existing without bodies as we do of
bodies actually existing without minds, the argument will stand only
if Descartes' clear and distinct understanding of the mind's nature
somehow guarantees the truth of premise 1; but, at this point, it is
not evident whether Descartes' "clear and distinct" perception
guarantees the truth of anything.
However, in the Fourth Meditation, Descartes goes to great lengths to
guarantee the truth of whatever is clearly and distinctly understood.
This veridical guarantee is based on the theses that God exists and
that he cannot be a deceiver. These arguments, though very
interesting, are numerous and complex, and so they will not be
discussed here. Suffice it to say that since Descartes believes he has
established God's inability to deceive with absolute, geometrical
certainty, he would have to consider anything contradicting this
conclusion to be false. Moreover, Descartes claims that he cannot help
but believe clear and distinct ideas to be true. However, if God put a
clear and distinct idea in him that was false, then he could not help
but believe a falsehood to be true and, to make matters worse, he
would never be able to discover the mistake. Since God would be the
author of this false clear and distinct idea, he would be the source
of the error and would, therefore, be a deceiver, which must be false.
Hence, all clear and distinct ideas must be true, because it is
impossible for them to be false given God's non-deceiving nature.
That said, the clarity and distinctness of Descartes' understanding of
mind and body guarantees the truth of premise 1. Hence, both "clear
and distinct" premises are not blunt, unjustified assertions of what
he believes but have very strong rational support from within
Descartes' system. However, if it turns out that God does not exist or
that he can be a deceiver, then all bets are off. There would then no
longer be any veridical guarantee of what is clearly and distinctly
understood and, as a result, the first premise could be false.
Consequently, premise 1 would not bar the possibility of minds
requiring brains to exist and, therefore, this premise would not be
absolutely certain as Descartes supposed. In the end, the conclusion
is established with absolute certainty only when considered from
within Descartes' own epistemological framework but loses its force if
that framework turns out to be false or when evaluated from outside of
it.
These guaranteed truths express some very important points about
Descartes' conception of mind and body. Notice that mind and body are
defined as complete opposites. This means that the ideas of mind and
body represent two natures that have absolutely nothing in common.
And, it is this complete diversity that establishes the possibility of
their independent existence. But, how can Descartes make a legitimate
inference from his independent understanding of mind and body as
completely different things to their independent existence? To answer
this question, recall that every idea of limited or finite things
contains the idea of possible or contingent existence, and so
Descartes is conceiving mind and body as possibly existing all by
themselves without any other creature. Since there is no doubt about
this possibility for Descartes and given the fact that God is all
powerful, it follows that God could bring into existence a mind
without a body and vice versa just as Descartes clearly and distinctly
understands them. Hence, the power of God makes Descartes' perceived
logical possibility of minds existing without bodies into a
metaphysical possibility. As a result, minds without bodies and bodies
without minds would require nothing besides God's concurrence to exist
and, therefore, they are two really distinct substances.
The Second Version
The argument just examined is formulated in a different way later in
the Sixth Meditation:
[T]here is a great difference between the mind and the body,
inasmuch as the body is by its very nature always divisible, while the
mind is utterly indivisible. For when I consider the mind, or myself
in so far as I am merely a thinking thing, I am unable to distinguish
any parts within myself; I understand myself to be something quite
single and complete….By contrast, there is no corporeal or extended
thing that I can think of which in my thought I cannot easily divide
into parts; and this very fact makes me understand that it is
divisible. This one argument would be enough to show me that the mind
is completely different from the body…. (AT VII 86-87: CSM II 59).
This argument can be reformulated as follows, replacing "mind" for "I"
as in the first version:
1. I understand the mind to be indivisible by its very nature.
2. I understand body to be divisible by its very nature.
3. Therefore, the mind is completely different from the body.
Notice the conclusion that mind and body are really distinct is not
explicitly stated but can be inferred from 3. What is interesting
about this formulation is how Descartes reaches his conclusion. He
does not assert a clear and distinct understanding of these two
natures as completely different but instead makes his point based on a
particular property of each. However, this is not just any property
but a property each has "by its very nature." Something's nature is
just what it is to be that kind of thing, and so the term "nature" is
here being used as synonymous with "essence." On this account,
extension constitutes the nature or essence of bodily kinds of things;
while thinking constitutes the nature or essence of mental kinds of
things. So, here Descartes is arguing that a property of what it is to
be a body, or extended thing, is to be divisible, while a property of
what it is to be a mind or thinking thing is to be indivisible.
Descartes' line of reasoning in support of these claims about the
respective natures of mind and body runs as follows. First, it is easy
to see that bodies are divisible. Just take any body, say a pencil or
a piece of paper, and break it or cut it in half. Now you have two
bodies instead of one. Second, based on this line of reasoning, it is
easy to see why Descartes believed his nature or mind to be
indivisible: if a mind or an "I" could be divided, then two minds or
"I's" would result; but since this "I" just is my self, this would be
the same as claiming that the division of my mind results in two
selves, which is absurd. Therefore, the body is essentially divisible
and the mind is essentially indivisible: but how does this lead to the
conclusion that they are completely different?
Here it should be noted that a difference in just any non-essential
property would have only shown that mind and body are not exactly the
same. But this is a much weaker claim than Descartes' conclusion that
they are completely different. For two things could have the same
nature, for example, extension, but have other, changeable properties
or modes distinguishing them. Hence, these two things would be
different in some respect, for example, in shape, but not completely
different, since both would still be extended kinds of things.
Consequently, Descartes needs their complete diversity to claim that
he has completely independent conceptions of each and, in turn, that
mind and body can exist independently of one another.
Descartes can reach this stronger conclusion because these essential
properties are contradictories. On the one hand, Descartes argues that
the mind is indivisible because he cannot perceive himself as having
any parts. On the other hand, the body is divisible because he cannot
think of a body except as having parts. Hence, if mind and body had
the same nature, it would be a nature both with and without parts. Yet
such a thing is unintelligible: how could something both be separable
into parts and yet not separable into parts? The answer is that it
can't, and so mind and body cannot be one and the same but two
completely different natures. Notice that, as with the first version,
mind and body are here being defined as opposites. This implies that
divisible body can be understood without indivisible mind and vice
versa. Accordingly each can be understood as existing all by itself:
they are two really distinct substances.
However, unlike the first version, Descartes does not invoke the
doctrine of clear and distinct ideas to justify his premises. If he
had, this version, like the first, would be absolutely certain from
within Descartes' own epistemological system. But if removed from this
apparatus, it is possible that Descartes is mistaken about the
indivisibility of the mind, because the possibility of the mind
requiring a brain to exist would still be viable. This would mean
that, since extension is part of the nature of mind, it would, being
an extended thing, be composed of parts and, therefore, it would be
divisible. As a result, Descartes could not legitimately reach the
conclusion that mind and body are completely different. This would
also mean that the further, implicit conclusion that mind and body are
really distinct could not be reached either. In the end, the main
difficulty with Descartes' real distinction argument is that he has
not adequately eliminated the possibility of minds being extended
things like brains.
4. The Mind-Body Problem
The real distinction of mind and body based on their completely
diverse natures is the root of the famous mind-body problem: how can
these two substances with completely different natures causally
interact so as to give rise to a human being capable of having
voluntary bodily motions and sensations? Although several versions of
this problem have arisen over the years, this section will be
exclusively devoted to the version of it Descartes confronted as
expressed by Pierre Gassendi, the author of the Fifth Objections, and
Descartes' correspondent, Princess Elizabeth of Bohemia. Their concern
arises from the claim at the heart of the real distinction argument
that mind and body are completely different or opposite things.
The complete diversity of their respective natures has serious
consequences for the kinds of modes each can possess. For instance, in
the Second Meditation, Descartes argues that he is nothing but a
thinking thing or mind, that is, Descartes argues that he is a "thing
that doubts, understands, affirms, denies, is willing, is unwilling,
and also imagines and has sensory perceptions" (AT VII 28: CSM II 19).
It makes no sense to ascribe such modes to entirely extended,
non-thinking things like stones, and therefore, only minds can have
these kinds of modes. Conversely, it makes no sense to ascribe modes
of size, shape, quantity and motion to non-extended, thinking things.
For example, the concept of an unextended shape is unintelligible.
Therefore, a mind cannot be understood to be shaped or in motion, nor
can a body understand or sense anything. Human beings, however, are
supposed to be combinations of mind and body such that the mind's
choices can cause modes of motion in the body, and motions in certain
bodily organs, such as the eye, cause modes of sensation in the mind.
The mind's ability to cause motion in the body will be addressed
first. Take for example a voluntary choice, or willing, to raise one's
hand in class to ask a question. The arm moving upward is the effect
while the choice to raise it is the cause. But willing is a mode of
the non-extended mind alone, whereas the arm's motion is a mode of the
extended body alone: how can the non-extended mind bring about this
extended effect? It is this problem of voluntary bodily motion or the
so-called problem of "mind to body causation" that so troubled
Gassendi and Elizabeth. The crux of their concern was that in order
for one thing to cause motion in another, they must come into contact
with one another as, for example, in the game of pool the cue ball
must be in motion and come into contact with the eight-ball in order
for the latter to be set in motion. The problem is that, in the case
of voluntarily bodily movements, contact between mind and body would
be impossible given the mind's non-extended nature. This is because
contact must be between two surfaces, but surface is a mode of body,
as stated at Principles of Philosophy part II, section 15.
Accordingly, the mind does not have a surface that can come into
contact with the body and cause it to move. So, it seems that if mind
and body are completely different, there is no intelligible
explanation of voluntary bodily movement.
Although Gassendi and Elizabeth limited themselves to the problem of
voluntary bodily movement, a similar problem arises for sensations, or
the so-called problem of "body to mind causation." For instance, a
visual sensation of a tree is a mode of the mind alone. The cause of
this mode would be explained by the motion of various imperceptible
bodies causing parts of the eye to move, then movements in the optic
nerve, which in turn cause various "animal spirits" to move in the
brain and finally result in the sensory idea of the tree in the mind.
But how can the movement of the "animal spirits," which were thought
to be very fine bodies, bring about the existence of a sensory idea
when the mind is incapable of receiving modes of motion given its
non-extended nature? Again, since the mind is incapable of having
motion and a surface, no intelligible explanation of sensations seems
possible either. Therefore, the completely different natures of mind
and body seem to render their causal interaction impossible.
The consequences of this problem are very serious for Descartes,
because it undermines his claim to have a clear and distinct
understanding of the mind without the body. For humans do have
sensations and voluntarily move some of their bodily limbs and, if
Gassendi and Elizabeth are correct, this requires a surface and
contact. Since the mind must have a surface and a capacity for motion,
the mind must also be extended and, therefore, mind and body are not
completely different. This means the "clear and distinct" ideas of
mind and body, as mutually exclusive natures, must be false in order
for mind-body causal interaction to occur. Hence, Descartes has not
adequately established that mind and body are two really distinct
substances.
5. Descartes' Response to the Mind-Body Problem
Despite the obviousness of this problem, and the amount of attention
given to it, Descartes himself never took this issue very seriously.
His response to Gassendi is a telling example:
These questions presuppose amongst other things an explanation of
the union between the soul and the body, which I have not yet dealt
with at all. But I will say, for your benefit at least, that the whole
problem contained in such questions arises simply from a supposition
that is false and cannot in any way be proved, namely that, if the
soul and the body are two substances whose nature is different, this
prevents them from being able to act on each other (AT VII 213: CSM II
275).
So, Descartes' response to the mind-body problem is twofold. First,
Descartes contends that a response to this question presupposes an
explanation of the union between the mind (or soul) and the body.
Second, Descartes claims that the question itself stems from the false
presupposition that two substances with completely different natures
cannot act on each other. Further examination of these two points will
occur in reverse order.
Descartes' principles of causation put forward in the Third Meditation
lie at the heart of this second presupposition. The relevant portion
of this discussion is when Descartes argues that the less real cannot
cause something that is more real, because the less real does not have
enough reality to bring about something more real than itself. This
principle applies on the general level of substances and modes. On
this account, an infinite substance, that is, God, is the most real
thing because only he requires nothing else in order to exist;
created, finite substances are next most real, because they require
only God's creative and conservative activity in order to exist; and
finally, modes are the least real, because they require a created
substance and an infinite substance in order to exist. So, on this
principle, a mode cannot cause the existence of a substance since
modes are less real than finite substances. Similarly, a created,
finite substance cannot cause the existence of an infinite substance.
But a finite substance can cause the existence of another finite
substance or a mode (since modes are less real than substances).
Hence, Descartes' point could be that the completely diverse natures
of mind and body do not violate this causal principle, since both are
finite substances causing modes to exist in some other finite
substance. This indicates further that the "activity" of the mind on
the body does not require contact and motion, thereby suggesting that
mind and body do not bear a mechanistic causal relation to each other.
More will be said about this below.
The first presupposition concerns an explanation of how the mind is
united with the body. Descartes' remarks about this issue are
scattered across both his published works and his private
correspondence. These texts indicate that Descartes did not maintain
that voluntary bodily movements and sensation arise because of the
causal interaction of mind and body by contact and motion. Rather, he
maintains a version of the form-matter theory of soul-body union
endorsed by some of his scholastic-Aristotelian predecessors and
contemporaries. Although a close analysis of the texts in question
cannot be conducted here, a brief summary of how this theory works for
Descartes can be provided.
Before providing this summary, however, it is important to disclaim
that this scholastic-Aristotelian interpretation is a minority
position amongst Descartes scholars. The traditional view maintains
that Descartes' human being is composed of two substances that
causally interact in a mechanistic fashion. This traditional view led
some of Descartes' successors, such as Malebranche and Leibniz (who
also believed in the real distinction of mind and body), to devise
metaphysical systems wherein mind and body do not causally interact
despite appearances to the contrary. Other philosophers considered the
mind-body problem to be insurmountable, thereby denying their real
distinction: they claim that everything is either extended (as is
common nowadays) or mental (as George Berkeley argued in the 18th
century). Indeed, this traditional, mechanistic interpretation of
Descartes is so deeply ingrained in the minds of philosophers today,
that most do not even bother to argue for it. However, a notable
exception is Marleen Rozemond, who argues for the incompatibility of
Descartes' metaphysics with any scholastic-Aristotelian version of
mind or soul-body union. Those interested in closely examining her
arguments should consult her book Descartes's Dualism. A book arguing
in favor of the scholastic-Aristotelian interpretation is entitled
Descartes and the Metaphysics of Human Nature; Chapter 5 specifically
addresses Rozemond's concerns.
Two major stumbling blocks Rozemond raises for the
scholastic-Aristotelian interpretation concern the mind's status as a
substantial form and the extent to which Descartes can maintain a form
of the human body. However, recall that Descartes rejects substantial
forms because of their final causal component. Descartes' argument was
based on the fact (as he understood it) that the scholastics were
ascribing mental properties to entirely non-mental things like stones.
Since the mind is an entirely mental thing, these arguments just do
not apply to it. Hence, Descartes' particular rejection of substantial
forms does not necessarily imply that Descartes did not view the mind
as a substantial form. Indeed, as Paul Hoffman noted:
Descartes really rejects the attempt to use the human soul as a model
for explanations in the entirely physical world. This makes it
possible that Descartes considered the human mind to be the only
substantial form. At first glance this may seem ad hoc but it is also
important to notice that rejecting the existence of substantial forms
with the exception of the mind or rational soul was not uncommon
amongst Descartes' contemporaries.
Although the mind's status as a substantial form may seem at risk
because of its meager explicit textual support, Descartes suggests
that the mind a "substantial form" twice in a draft of open letter to
his enemy Voetius:
Yet, if the soul is recognized as merely a substantial form, while
other such forms consist in the configuration and motion of parts,
this very privileged status it has compared with other forms shows
that its nature is quite different from theirs (AT III 503: CSMK
207-208).
Descartes then remarks "this is confirmed by the example of the soul,
which is the true substantial form of man" (AT III 508: CSMK 208).
Although other passages do not make this claim explicitly, they do
imply (in some sense) that the mind is a substantial form. For
instance, Descartes claims in a letter to Mesland dated 9 February
1645, that the soul is "substantially united" with the human body (AT
IV 166: CSMK 243). This "substantial union" was a technical term
amongst the scholastics denoting the union between a substantial form
and matter to form a complete substance. Consequently, there is some
reason for believing that the human mind is the only substantial form
left standing in Descartes' metaphysics.
Another major stumbling block recognized by Rozemond is the extent to
which, if any, Descartes' metaphysics can maintain a principle for
organizing extension into a human body. This was a point of some
controversy amongst the scholastics themselves. Philosophers
maintaining a Thomistic position argued that the human soul is the
human body's principle of organization. While others, maintaining a
basically Scotistic position, argued that some other form besides the
human soul is the form of the body. This "form of corporeity"
organizes matter for the sake of being a human body but does not
result in a full-fledged human being. Rather it makes a body with the
potential for union with the human soul. The soul then actualizes this
potential resulting in a complete human being. If Descartes did hold a
fundamentally scholastic theory of mind-body union, then is it more
Thomistic or Scotistic? Since intellect and will are the only
faculties of the mind, it does not have the faculty for organizing
matter for being a human body. So, if Descartes' theory is scholastic,
it must be most in line with some version of the Scotistic theory.
Rozemond argues that Descartes' rejection of all other substantial
forms (except the human mind or soul) precludes this kind of theory
since he cannot appeal to the doctrine of substantial forms like the
Scotists.
Although Descartes argues that bodies, in the general sense, are
constituted by extension, he also maintains that species of bodies are
determined by the configuration and motion of their parts. This
doctrine of "configuration and motion of parts" serves the same
purpose as the doctrine of substantial forms with regards to entirely
physical things. But the main difference between the two is that
Descartes' doctrine does not employ final causes. Recall that
substantial forms organize matter for the purpose of being a species
of thing. The purpose of a human body endowed with only the form of
corporeity is union with the soul. Hence, the organization of matter
into a human body is an effect that is explained by the final cause or
purpose of being disposed for union. But, on Descartes' account, the
explanatory order would be reversed: a human body's disposition for
union is an effect resulting from the configuration and motion of
parts. So, even though Descartes does not have recourse to substantial
forms, he still has recourse to the configuration of matter and to the
dispositions to which it gives rise, including "all the dispositions
required to preserve that union" (AT IV 166: CSMK 243). Hence, on this
account, Descartes gets what he needs, namely, Descartes gets a body
properly configured for potential union with the mind, but without
recourse to the scholastic notion of substantial forms with their
final causal component.
Another feature of this basically Scotistic position is that the soul
and the body were considered incomplete substances themselves, while
their union results in one, complete substance. Surely Descartes
maintains that mind and body are two substances but in what sense, if
any, can they be considered incomplete? Descartes answers this
question in the Fourth Replies. He argues that a substance may be
complete insofar as it is a substance but incomplete insofar as it is
referred to some other substance together with which it forms yet some
third substance. This can be applied to mind and body as follows: the
mind insofar as it is a thinking thing is a complete substance, while
the body insofar as it is an extended thing is a complete substance,
but each taken individually is only an incomplete human being.
This account is repeated in the following excerpt from a letter to
Regius dated December 1641:
For there you said that the body and the soul, in relation to the
whole human being, are incomplete substances; and it follows from
their being incomplete that what they constitute is a being through
itself (that is, an ens per se; AT III 460: CSMK 200).
The technical sense of the term "being through itself" was intended to
capture the fact that human beings do not require any other creature
but only God's concurrence to exist. Accordingly, a being through
itself, or ens per se, is a substance. Also notice that the claim in
the letter to Regius that two incomplete substances together
constitute a being through itself is reminiscent of Descartes' remarks
in the Fourth Replies. This affinity between the two texts indicates
that the union of mind and body results in one complete substance or
being through itself. This just means that mind and body are the
metaphysical parts (mind and body are incomplete substances in this
respect) that constitute one, whole human being, which is a complete
substance in its own right. Hence, a human being is not the result of
two substances causally interacting by means of contact and motion, as
Gassendi and Elizabeth supposed, but rather they bear a relation of
act and potency that results in one, whole and complete substantial
human being.
This sheds some light on why Descartes thought that an account of
mind-body union would put Gassendi's and Elizabeth's concerns to rest:
they misconceived the union of mind and body as a mechanical relation
when in fact it is a relation of act and potency. This avoids
Gassendi's and Elizabeth's version of this problem. This aversion is
accomplished by the fact that modes of voluntary motion (and
sensations, by extrapolation) should be ascribed to a whole human
being and not to the mind or the body taken individually. This is made
apparent in a 21 May 1643 letter to Elizabeth where Descartes
distinguishes between various "primitive notions." The most general
are the notions of being, number, duration, and so on, which apply to
all conceivable things. He then goes on to distinguish the notions of
mind and body:
Then, as regards body in particular, we have only the notion of
extension, which entails the notions of shape and motion; and as
regards the soul on its own, we have only the notion of thought, which
includes the perceptions of the intellect and the inclinations of the
will (AT III 665: CSMK 218).
Here body and soul (or mind) are primitive notions and the notions of
their respective modes are the notions "entailed by" or "included in"
these primitives. Descartes then discusses the primitive notion of
mind-body union:
Lastly, as regards the soul and the body together, we have only
the notion of their union, on which depends our notion of the soul's
power to move the body, and the body's power to act on the soul and
cause its sensations and passions (AT III 665: CSMK 218).
In light of the immediately preceding lines, this indicates that
voluntary bodily movements and sensations are not modes of the body
alone, or the mind alone, but rather are modes of "the soul and the
body together." This is at least partially confirmed in the following
lines from Principles, part I, article 48:
But we also experience within ourselves certain other things,
which must not be referred either to the mind alone or to the body
alone. These arises, as will be made clear in the appropriate place,
from the close and intimate union of our mind with the body. This list
includes, first, appetites like hunger and thirds; secondly, the
emotions or passions . . . (AT VIIIA 23: CSM I 209).
These texts indicate that the mind or soul is united with the body so
as to give rise to another whole complete substance composed of these
two metaphysical parts. And, moreover, this composite substance now
has the capacity for having modes of its own, namely, modes of
voluntary bodily movement and sensation, which neither the mind nor
the body can have individually. So, voluntary bodily movements are not
modes of the body alone caused by the mind, nor are sensations modes
of the mind alone caused by the body. Rather, both are modes of a
whole and complete human being. On this account, it makes no sense to
ask how the non-extended mind can come into contact with the body to
cause these modes. To ask this would be to get off on the wrong foot
entirely, since contact between these two completely diverse
substances is not required for these modes to exist. Rather all that
is necessary is for the mind to actualize the potential in a properly
disposed human body to form one, whole, human being to whom is
attributed modes of voluntary movement and sensation.
Although the scholastic-Aristotelian interpretation avoids the
traditional causal interaction problem based on the requirements of
contact and motion, it does run up against another version of that
problem, namely, a problem of formal causation. This is a problem
facing any scholastic-Aristotelian theory of mind or soul-body union
where the soul is understood to be an immaterial substantial form.
Recall that the immaterial mind or soul as substantial form is suppose
to act on a properly disposed human body in order to result in a
full-fledged human being. The problem of formal causal interaction is:
how can an immaterial soul assubstantial form act on the potential in
a material thing? Can any sense be made of the claim that a
non-extended or immaterial things acts on anything? Descartes noticed
in a letter to Regius (AT III 493: CSMK 206) that the scholastics did
not try to answer this question and so he and Regius need not either.
The likely explanation of their silence is that the act-potency
relation was considered absolutely fundamental to
scholastic-Aristotelian philosophy and, therefore, it required no
further explanation. So, in the end, even if Descartes' theory is as
described here, it does not evade all the causal problems associated
with uniting immaterial souls or mind to their respective bodies. ,
However, if this proposed account is true, it helps to cast Descartes'
philosophy in a new light and to redirect the attention of scholars to
the formal causal problems involved.
6. References and Further Reading
Primary Sources
* Descartes, Rene, Ouevres de Descartes, 11 vols., eds. Charles
Adam and Paul Tannery, Paris: Vrin, 1974-1989.
o This is still the standard edition of all of Descartes'
works and correspondence in their original languages. Cited in the
text as AT, volume, page.
* Descartes, Rene, The Philosophical Writings of Descartes, 3
vols., trans. John Cottingham, Robert Stoothoff, Dugald Murdoch and
Anthony Kenny, Cambridge: Cambridge University Press, 1984-1991
o This is the standard English translation of Descartes
philosophical works and correspondence. Cited in the text as CSM or
CSMK, volume, page.
Secondary Sources
* Broughton, Janet and Mattern, Ruth, "Reinterpreting Descartes on
the Notion of the Union of Mind and Body," Journal of the History of
Philosophy 16 (1978), 23-32.
o A reinterpretation of the notion of mind-body union in the
correspondence with Elizabeth, which addresses Radner's interpretation
of it. See below.
* Garber, Daniel, "Understanding Interaction: What Descartes
Should Have Told Elizabeth," Southern Journal of Philosophy, Supp. 21
(1983), 15-32.
o Article addressing the issues of the primitive notions and
how this theory should be used to explain mind-body causal interaction
to Elizabeth.
* Hoffman, Paul, "The Unity of Descartes' Man," The Philosophical
Review 95 (1986), 339-369.
o Article arguing that Descartes' theory of mind-body union
is more in line with scholastic-Aristotelian theories of soul-body
union than previously supposed.
* Kenny, Anthony, Descartes: A Study of His Philosophy, New York:
Random House, 1968. See especially chapters 4 and 10.
o These chapters provide classic interpretations of the real
distinction between mind and body and the mind-body problem.
* Mattern, Ruth, "Descartes' Correspondence with Elizabeth
Concerning both the Union and Distinction of Mind and Body" in
Descartes: Critical and Interpretive Essays, ed. Michael Hooker,
Baltimore: John Hopkins University Press, 1978, 212-222.
o Short essay examining Descartes' correspondence with
Elizabeth on this issue and how it was supposed to direct her to a
correct understanding of mind-body causal interaction.
* Radner, Daisie, "Descartes' Notion of the Union of Mind and
Body," Journal of the History of Philosophy 9 (1971), 159-170.
o This is the first article in Anglo-American scholarship to
address the issue of mind-body union. It addresses several texts,
including the letter to Elizabeth enumerating the primitive notions.
* Rozemond, Marleen, Descartes's Dualism, Cambridge: Harvard
University Press, 1998.
o This book argues for a particular understanding of the
real distinction between mind and body that would preclude Hoffman's
scholastic-Aristotelian account of their union.
* Skirry, Justin, Descartes and the Metaphysics of Human Nature,
London and New York: Thoemmes-Continuum Press, 2005.
o This book takes issue with Rozemond's account of the
mind-body union through a close re-examination of fundamental features
of Descartes' metaphysics and by building on certain features of
Hoffman's account.
* Voss, Stephen, "Descartes: The End of Anthropology" in Reason,
Will and Sensation, ed. John Cottingham, Oxford: Clarendon Press,
1994.
o This essay provides a close textual analysis of Descartes'
account of the union of mind and body on the supposition that he
maintained a Platonic rather than scholastic-Aristotelian theory of
mind-body union.
* Williams, Bernard, Descartes: The Project of Pure Enquiry,
Sussex: Harvester Press, 1978. See especially chapter 4.
o This is another classic account of the mind-body relation
in Descartes.
* Wilson, Margaret, Descartes, London and Boston: Routledge and
Kegan Paul, 1978.
o Provides classic accounts of the real distinction argument
and issues concerning mind-body causal interaction.
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