Knowledge Is Not Ultimately Sense Knowledge
Classic Philosophical Questions Part 5 - Knowledge
René Descartes, from the Meditations
Kem Stone - 11 October 2007
To represent the rationalist viewpoint in epistemology, the editors have chosen Descartes’ Meditations I and II, in
which Descartes argues that we cannot be certain of anything other than the proposition, “I think, therefore I am”
and that the mind can be more clearly and distinctly perceived than corporeal objects.  I have always enjoyed
these particular meditations, finding their insights clever and quite valuable in some aspects, particularly in regard
to methodological doubt.  It is not until the third meditation that I begin to disagree with Descartes, so although I
ultimately reject the Cartesian position, I will not be offering much criticism in this particular exposition.

Descartes begins his meditations by reflecting on how many of his previously held beliefs have turned out to be
false, and that he will now endeavour to strip his mind bare of all assumptions and work from the ground up to see
if any indubitable knowledge remains.  “But in as much as reason already persuades me that I ought no less
carefully to withhold my assent from matters which are not entirely certain and indubitable than from those which
appear to me manifestly to be false, if I am able to find in each one some reason to doubt, this will suffice to justify
my rejecting the whole” (248).  This is the process of methodological doubt.  In order to rid himself of all false
opinions, he must immediately reject any belief whatsoever that is subject to doubt, even if that belief is likely to be

First and foremost, any beliefs which he has accepted that have been formed through the senses are subject to
doubt, as the senses are sometimes deceptive, and therefore can not be trusted on all occasions.  Even so,
Descartes does not believe it can be reasonably doubted that he is where he seems to be, dressed and seated by
the fire with paper in hand and so forth.  Yet even these beliefs are not immune to doubt, as he has often dreamed
that he was dressed and seated by the fire when in actuality he was undressed and lying in bed.  It may certainly
seem that he is not dreaming, but he is deceived into believing he is awake even when he is dreaming.  “I remind
myself that on many occasions I have in sleep been deceived by similar illusions, and in dwelling carefully on this
reflection I see so manifestly that there are no certain indications by which we may clearly distinguish wakefulness
from sleep that I am lost in astonishment” (248).  Therefore we cannot trust the senses because we can never be
completely certain that we are not dreaming.

Yet it would still seem that we can be certain of the existence of corporeal objects, as even the objects in dreams
must be based on something with actual existence, in the same manner as painted representations.  Furthermore,
corporeal objects have certain aspects such as figure, extension, quantity or magnitude, that belong to the sciences
of Arithmetic and Geometry, which seem to contain some measure of certainty.  Whether one is awake or asleep,
the sum of two and three will be five, and a square can never have more than four sides.  Yet if Descartes is, as he
believes, the creation of an all-powerful God, he can not even be certain of these matters.  “How do I know that
He has not brought it to pass that there is no earth, no heaven, no extended body, no magnitude, no place, and
that nevertheless they seem to me to exist just exactly as I now see them…how do I know that I am not deceived
every time that I add two and three, or count the sides of a square, or judge of things yet simpler?” (249).

But Descartes, who subscribes to the Judeo-Christian conception of God as an all-powerful, infinitely good being,
does not believe God would deceive him into holding false beliefs, as he sees deception as an inherent evil and
God being omnipotent would not need nor desire to use evil to achieve any of his ends.  Therefore Descartes
imagines that an evil demon of great power has employed all his energies to the purpose of deceiving him.  The
heavens and the earth, every corporeal object, even down to his own body, he will consider a mere illusion
brought about by the influence of this demon.  “I shall remain obstinately attached to this idea, and if by this means
it is not in my power to arrive at the knowledge of any truth, I may at least do what is in my power and with firm
purpose avoid giving credence to any false thing, or being imposed upon by this arch deceiver, however powerful
and deceptive he may be” (250).

The “evil demon” scenario can be taken as the essence of Descartes’ argument against empiricism, which holds
that knowledge comes
only through the senses.  According to Descartes, we can never be certain of the
knowledge that comes to us through the senses because it may have been placed there by an evil demon who
wishes to trick us into believing things exist which do not exist, or things are true which are not true.  This
hypothesis is one that can never be completely refuted, as although none of us believe we are really being tricked
in such a manner by an evil demon, we can never know for certain whether it is not the case that the evil demon
has deceived us into believing we are not being deceived.

In the second meditation, Descartes returns to the idea that an evil demon is engaged in deceiving him regarding all
of his beliefs, and considers whether there is one single belief he that is
not subject to doubt.  He can not be
certain of the existence of a God or even of the deceiver, because he could be generating his own beliefs.  
Regarding his own existence, he has already denied that he has a body and senses, but here he pauses.  Even
without body and senses, Descartes says, he must still be something.  “I was persuaded that there were no minds,
nor any bodies: was I not then likewise persuaded that I did not exist?  Not at all; of a surety I myself did exist
since I persuaded myself of something…So that after having reflected well and carefully examined all things, we
must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I
pronounce it, or that I mentally conceive it” (251).  Descartes has discovered at last one belief that is not subject
to doubt, the belief in his own existence.

From there he must determine what exactly he is.  He is a thing with hands, arms, and so on which constitute his
body.  He is also a thing that walks and feels and takes nourishment, which he attributes to the soul.  But upon
careful consideration, keeping in mind that a demon may be deceiving him, he finds that of the things that pertain to
the body, he does not really possess any one of them.  As to the attributes of the soul, he cannot walk or feel or
take nutrition without a body, so these do not belong to him either.  But as for thinking, “I find here that thought is
an attributable that belongs to me; it alone cannot be separated from me.  I am, I exist, that is certain.  But how
often?  Just when I think: for it might possibly be the case if I ceased entirely to think, that I should likewise cease
altogether to exist” (252).  Descartes now knows that he exists, and he exists as a thing which thinks.

The question now becomes what is a thing which thinks.  As a thinking being, Descartes also possesses the power
of the many attributes of thought: affirming, denying, willing, refusing, doubting and understanding among them.  He
also possesses the power of imagination, as even if everything he imagines is false, it cannot be denied that he
imagines.  Finally, he can attribute sensation to himself as well, as even if every phenomenon that comes to him
through the senses is illusory, it still
seems to him that he senses them.  In this sense, sensation is the same as

Descartes now turns to the somewhat counter-intuitive consequences of this line of reasoning.  If he can only be
certain of his own existence as a thinking being, then the mind is more easily knowable than the objects of the
mind.  Yet it seems that the objects of imagination are far clearer and more distinctly known than the imagination
itself.  It seems that corporeal objects, whose existence are highly dubious, are more easily known than the mind,
though its existence is certain.

To challenge the common-sense view, Descartes considers an object that we would believe to be quite distinctly
comprehended, such as a piece of wax.  He enumerates its properties: it has the odour of flowers, a definite size,
colour, and figure, it is hard and cold, and it makes a sound when struck with the finger.  Yet when the wax is held
to the fire, these properties change.  The smell evaporates, the colour and figure changes, its size increases, and as
a liquid no sound is emitted when it is struck.  We know that it is the same wax, but how do we know?  “What
then did I know so distinctly in this piece of wax?  It could certainly be nothing of all that the senses brought to my
notice, since all these things which fall under taste, smell, sight, touch, and hearing are found to be changed, and
yet the same wax remains” (254).

He considers whether he knows it is the same wax not from its particular properties, but simply that it is a body
which shortly before had appeared under these forms now appears under others.  Yet if he abstracts all of the
qualities of the wax, all that remains is an extended thing with a flexible figure.  Yet its figure is not so easily
conceived, as flexibility is more than simply an ability to pass from a square to a triangular figure and so on, and
the imagination is incapable of encompassing the infinitude of all its possible forms.  The same applies to the
extension, as the wax will become larger and larger as it is heated, and can receive more variations in its extension
than can be imagined.

What follows from this is that “perception is neither an act of vision, nor of touch, nor of imagination, and has
never been such although it may have appeared formerly to be so, but only an intuition of the mind” (255).  
Objects then, according to Descartes, are not known through the senses but through intuitions of the mind.  To
illustrate this point further, Descartes considers that if we knew objects by vision alone, he could not claim to
know that there are men walking outside.  If they were merely hats and coats that covered automatic machines, it
would look exactly the same.  It is by intuition alone that he knows they are men and not machines.

Finally, what is most abundantly clear is that the wax cannot be perceived without the human mind.  “For if I judge
that the wax is or exists from the fact that I see it, it certainly follows much more clearly that I am or that I exist
from the fact that I see it.  For it may be that what I see is not really wax, it may also be that I do not possess eyes
with which to see anything; but it cannot be that when I see, or…when I think I see, that I myself who think am
nought” (256).  We therefore return to the claim of
cogito ergo sum, having seen that the existence of the mind
actually is clearer to the understanding than any corporeal objects that we know of through the mind.

I do not have much to say in reaction to Descartes’ first two meditations.  I would remark that as much of a
sceptic as I am, and as dearly as I hold to the opinion that nothing can be known for certain, the
cogito does point
the way to one certain thing: the existence of thought.  Descartes believes he can be certain of his own existence,
but I do not believe the existence of an isolated ego is certain.  There could be thought without a thinker—the ego
itself merely another illusion.  Yet this one indubitable proposition is hardly remarkable when examined closely: all
that can be proven by thinking is the existence of thinking itself.  And because nothing else can be known for
certain merely by the process of thought alone, this circular proof is basically all that rationalism amounts to.