The proof of
the existence of material things
Let us now turn to Meditation VI. Do material things exist? Well,
they exist as the subject matter of pure mathematics -- and thus as
objects of the understanding. That material things exist is also suggested
by the imagination. The imagination is the application of the cognitive
faculty to a body which is intimately present to it, and which therefore
exists. (Rubin Pg. 40) The example of the pentagon and the chilliagon
distinguish the intellect from the imagination. You should try the
experiment of producing a mental image of a pentagon and then a chiliagon.
The pentagon (with its five sides) has few enough sides so that we can
form a distinct mental image of it. The chiliagon (with a thousand sides)
has too many sides for us to form a distinct mental image of it. The idea
of the pentagon, since it is a mental image, belongs to the imagination.
On the other hand, while we have a clear and distinct idea of the
chiliagon, that idea is not an image. The idea of the chiliagon is thus
not of the imagination. Rather, it is a creature of the understanding.
Descartes then argues that the imagination is not part of his essence.
(Rubin Pg. 41) (Here we are getting a bit more about the self -- its
essence is the understanding which grasps clear and distinct truths.) The
nature of the imagination leads to an argument by inference to the best
explanation for the existence of bodies. An inference to the best
explanation says that if there is one explanation of a phenomena which is
more likely than other competing explanations, this provides evidence that
that explanation is true. Here Descartes says: "...it is easy to see how
I get mental images if we suppose that my body exists. And, since I don't
have in mind any other plausible explanation of my ability to have mental
images, I conjecture that physical objects probably do exist. But this
conjecture is only probable."
So, there were going to be three proofs for the existence of external
bodies -- one from the understanding, one from imagination and one from
the senses. We looked at the one from the understanding -- insofar as
material bodies are objects of pure mathematics it is clear that they
exist; one from the imagination -- insofar as I have these images, the
best explanation of them is that they are caused by external objects; and
finally Descartes turns to the senses, since they presumably have to do
with the causes of these images. (Rubin Pg. 42)
from the senses.
Now we will consider the proof from the senses. On Pg. 42 Descartes
says, he will (1) "go back over all the things which I previously took to
be perceived by the senses, and recognized to be true, and my reasons for
thinking this." (2) Next he will set out his reasons for calling these
things into doubt. and (3) He will consider what he should now believe
|TEXT MAP: THE PROOF OF
THE EXISTENCE OF EXTERNAL OBJECTS FROM THE SENSES||(1) goes from 42 to 43|| (2) from 43 to 44 and
||(3) from 44 to 46 in
the paragraph which ends "...of pure mathematics.|
In (1) Descartes begins
with a list of things which he took to exist -- "heads, hands and feet,
and other limbs making up my body, which I regarded as part of myself, or
even perhaps as my whole self. Second this body is situated among other
bodies, which could effect his body in various favorable or unfavorable
ways, the favorable ones being indicated by pleasure and the unfavorable
by pain. In addition, Descartes had sensations within him of hunger,
thirst, and other such appetites, and physical propensities towards
emotions, such as cheerfulness, sadness and anger. Considering the bodies
outside him, he had tactile, and visual qualities which allowed him to
distinguish, the sky the earth, the seas and other bodies.
He also thought that while his ideas of such things were the only
immediate objects of sensory awareness, it was not unreasonable of him to
think that these were caused by objects which were distinct from him. For
the ideas came to him without his consent, and there could be no sensory
awareness of an object unless it was present to him, nor could he avoid
being aware of it if it was present. And these sensory ideas were much
more alive and vivid that ideas which he took from his memory. He also
had the notion that the ideas resembled these things. The senses preceded
the use of reason and the ideas of reason were less vivid than those
provided by the senses and derived from them. This led him to the
empiricist axiom -- that there is nothing in the intellect which did not
previously come from the senses. (Pg. 43) He also argues that he had good
reason to hold that his body was special in that it was his. There were
various things about his body which were taught to him by nature -- e.g.
that a tugging sensation in the stomach should tell him that he should eat
-- this had to be taught be nature because there is no obvious connection
between cause and effect.
(2) Then on Pg. 43 (last
paragraph) he gives the reasons why he came to doubt these things.
- Towers seen at a distance.
- Pain in limbs which are not there undermined his faith in the internal
- The dream hypothesis -- Pg. 114
- The hypothesis that my nature might lead me to error.
(3) Now as 3 starts we get a
surprise -- a proof for the real distinction of the mind and the body!
What is this doing here?
Next we get the distinction between reason or understanding which is
Descartes essence, and imagination and sensory perception which are
faculties which belong to him, but which are not part of his essence. He
distinguished between modes and substances of thinking and extended
On Pg. 45 we get the start of what we need for the proof from the
senses of the existence of external objects. First Descartes
distinguishes between a faculty of passive and a faculty of active
perception. The passive faculty receives the images, while the active
one produces them. He then considers the possibility that the active
faculty of perception could be in him. He rejects this because it
presupposes no intellectual act on his part, and the ideas in question are
produced without his cooperation and often even against his will. So,
the only alternative is that another substance distinct from him which
contains either formally or eminently those ideas. How does Descartes
proceed to argue from here that material substances must be the cause of
his sensory ideas?
Pg. 46 Material objects do not exist exactly as I perceive them -- but
one can distinguish here between those properties which are the objects of
pure mathematics and those which are confused.
Pg. 46 What nature teaches me. I have a body. I am intermingled with
my body -- here we get the not like a sailor in a ship metaphor.
Pg. 47 I am taught by nature that various other bodies exist in the
vicinity of my body. These bodies possess differences corresponding to my
differing perception, even if they do not resemble them.
Pg. 47 The things which I really was not taught by nature.
Pg. 48 This leads to rationalism and a rejection of empiricism.
Pg. 48-9 The issue of false judgment arises from the fact that
Descartes has gotten to the point where he is discriminating between true
and false beliefs about external objects. Thus at about 83 he is telling
us that while feelings of heat and pain result from being near the fire,
there is no reason for him to believe that there is anything in the fire
which resembles heat and pain. (So we are wrong in thinking that ideas of
sensible or secondary qualities resemble the qualities in the object).
Another example is to conclude that the void exists because nothing is
perceived between two objects. And the point of these example is that:
"But I mistreat them as reliable touchstones for immediate judgment about
the essential nature of bodies located outside of us; yet this is an area
where they provide only obscure information." So, it appears, this is an
application of the theory of error in MED. IV.
Now we turn to cases where nature presents objects for me to seek out
and avoid, and the internal sensations where I have detected errors.
First we have the poison case. Nature drives one towards what is normally
a good thing. The fact that it is bad in this case would require greater
knowledge than one has any reason to expect that one would have. So, in
this case nature does not urge us towards something bad.
But there are cases where nature does urge us towards something, and it
turns out to be the wrong course to take. Those who are ill may desire
food which (presumably) they know is bad for them. Here we get the
analogy with the clock, and the clock not telling time as much according
to the laws of nature as something which does tell time. Here Descartes
makes the distinction between two concepts of nature, one in the things
themselves, another imposed by me.
Descartes then admits that in the case of the body suffering from
dropsy, the term nature is not used as an extraneous label. In respect to
the composite of mind and body, there is a real error of nature here,
namely that it is thirsty at a time when drink will cause it harm. How is
it, then Descartes asks, that the goodness of God prevents us from being
deceived in this case? (Pg. 119)
Descartes first observation is to make the real distinction between the
mind and the body again, this time in terms of the simplicity argument.
Descartes second observation that the mind is not affected by all parts
of the body but by the brain or a small part of the brain (the pineal
gland). He continues: "Every time this part of the brain is in a given
state, it presents the same signals to the mind, even though the other
parts of the body may be in a different condition at that time." This
makes error possible.
Descartes third observation is that any part of the body which is moved
by some other part some distance away, can be moved by an intermediate
Descartes fourth observation is that any given movement occurring in
that part of the brain that immediately effects the mind produces just one
corresponding sensation, and thus the best system that could be divised is
that it produce that one sensation which of all possible sensations, is
most especially and most frequently conducive to the preservation of man.