I. DESCARTES' THEORY OF KNOWLEDGE
is a rationalist who set out to refute radical skepticism on its
He sought an
absolute foundation for knowledge by proposing to doubt
all things and accept as knowledge (or at least as a foundation for
knowledge) only what could not be doubted. (Note that this requirement
of absolute certainty [undoubtability] was not Plato's or Aristotle's
criterion for knowledge.)
procedure is to withhold his belief from anything that is not
entirely certain and indubitable.
him to consider the possibility that instead of a benevolent God,
there is a powerful and evil demon systematically deceiving him into
thinking things to be so that are not in fact so. This leads him to conclude
as doubtable, and therefore as not knowledge,
sense experience, and all that sense experience testifies to (e.g., that
there is an external world, other people, and even that he has a
his conviction that what he takes to be waking reality is real and not a
dream (or a cosmic deception),
his memory, and
intellectual calculation (e.g., 2 + 3 = 5).
3. The one
thing Descartes finds to be absolutely certain in the midst of
radical doubt and possible deception is that thinking (especially in the
mode of doubt) exists, that he as a thinking thing exists.
This will become Descartes' foundational truth and the measure of all other truth: Cogito [I think], ergo [therefore] sum [I am].4. From there Descartes investigates, solely on the basis of dialectical
a. What must be the criterion of knowledge -- namely, a candidate
belief whose certainty is wholly evident to the reflecting mind with
the "clarity and distinctness" of the cogito's existence to itself;
b. What his essential nature must be -- namely, a thing that thinks
(including also doubts, understands, affirms, denies, wills, refuses,
imagines, and feels); and
c. What, to the contrary, must be the essential nature of the bodies to
which our senses uncertainly testify -- namely, things which are
extended in space.
goes on to extend his foundation for knowledge and show
how it can provide a basis for the general trustworthiness of sense
perception, memory, and intellectual calculation, among other things,
by offering what he believes to be proof of the existence and goodness
of an infinitely powerful, wise, and good creator of himself (as a finite
and fallible mind), a creator whose goodness would never allow his
creature to be comprehensively deceived.
6. Thus Descartes
believes he has provided a foundation, on the one
hand, for knowledge in morality and religion (in the mind's or soul's
givenness to itself) and, on the other hand, for knowledge in the natural
sciences (in the nature of physical bodies to which the senses give us
II. DESCARTES' THEORY OF ERROR
1. Error results
because we tend to jump to conclusions, make judgments
too quickly on imperfect evidence. I.e., we make mistakes because we
do not exercise our capacity to suspend judgment: we assent or
dissent before we have enough evidence.
2. We can avoid
mistakes and achieve certainty if we hold back and
assent only to those propositions which we clearly and distinctly
perceive to be true (i.e., propositions for which we have fully sufficient
3. When we
confront a statement for which there is no compelling
evidence either that it is true or that it is false (where the truth is not
perceived with sufficient clarity and distinctness), we should suspend
our judgment until we have compelling evidence.
4. We shall
unquestionably reach the truth, if only we give sufficient
attention to all the things which we perfectly understand, and separate
these from all the other cases where our apprehension is more
confused and obscure.
5. Every clear
and distinct perception must have God for its author and
thus it cannot be deceptive, because God is no deceiver.
III. SOME PROBLEMS WITH DESCARTES' METHOD
upon a standard of absolute certainty eliminates the middle
ground of reasonable evidence. It suggests that if you don't have
complete certainty you have no evidence at all.
upon absolute clarity and distinctness to the skeptical
reflecting mind eliminates consideration of any respect in which reality
transcends full and determinate representation.
to rebuild one's knowledge from the ground up because a
number of things that once seemed true have become doubtful or false,
as Descartes does, is a lot like being in a boat out on the ocean and
proposing to abandon ship in order to rebuild the boat from the keel up
just because it has developed a few leaks.
working method of radical doubt may create more problems
than he supposes. In particular, it seems to put one in a very peculiar,
abstracted state of mind where the usual clues on which we rely to
orient ourselves and make sense of things are no longer available. In
other words, it may serve to cut us off from reality rather than put us
more closely in touch with reality.
A. It disables
reliance upon methodological faith, such that knowledge
by acquaintance (whether in sense perception or in reasoned
intuition) seems no longer trustworthy.
B. It makes experience seem passive, surface only, without depth and
C. It cuts the mind (and all internal mental life) off from its sense of being
in the world, being in context, situated in a time, place, culture,
language, and in rapport with other people -- also from learning
IV. INSTEAD OF ABSOLUTE CERTAINTY AS A CRITERION
1. If absolute
certainty is not the standard or criterion of knowledge, then
what is the standard?
to knowledge are fallible. They can be wrong. To make a
claim to knowledge is to risk being wrong. To make a claim to knowledge
is like making a wager or, alternatively, like making a promise, giving one's
word, that something is so.
is always some room for doubt. The criterion is to eliminate or
answer reasonable doubt, through having and offering sufficient
evidence. (See the handout on the nature and criticism of arguments.)
What sufficient evidence is will vary with the context and type of
knowledge being claimed.
2. But that won't convince the skeptic, will it?
needs to be convinced only if
(a) he is being reasonable in his doubt,
(b) he is really interested in getting at the truth in question, and
(c) he is truly open to weighing relevant reasons.
If he is not, his opinion ceases to count in reasonable argumentation until
he meets these conditions.
V. DESCARTES' ARGUMENT FOR THE
EXISTENCE OF A NON-DECEIVING,
goal: to refute the possibility that there could be an all
powerful, demonic higher power (an "evil genius") systematically
deceiving us (with regard to the general trustworthiness of sense
perception and the reliability of reason).
A. We have a clear and distinct idea of God.
B. This is
the idea of a perfect being, an infinite substance, eternal and
unchanging, supremely intelligent and powerful, existing
independently -- a being which created ourself and everything else
[whatever else exists].
cannot arise from nothing. (I.e., everything must have a
D. A cause
must contain at least as much reality (as much perfection) as
its effect. (I.e., what is more perfect cannot arise from what is less
E. Being an
imperfect and finite (limited) being, we cannot ourself produce
this idea of a perfect being.
F. Therefore, God must exist as the being who has produced in his
creature, namely us, the idea of a perfect being (God himself.)
G. All fraud
and deceit depend upon some defect.
H. Therefore, God cannot be a deceiver.
I. The only
reason for doubting that human reason is reliable is the
possibility of a higher power deceiving us (the Evil Genius hypothesis).
J. Therefore, human reason is reliable.
Doesn't this proof assume that human reason is reliable, and
thus assume the very thesis it is trying to prove? I.e., does it not "argue in
VI. DESCARTES' IDEA OF OUR KNOWLEDGE OF THE EXTERNAL WORLD
goal: to establish a firm foundation on the basis of which
natural science can proceed to achieve an understanding of things that
will make us "masters and possessors of nature."
science seeks knowledge of the external world.
a. The external world is made up of extended things, bodies in space
-- and determinately representable in mathematical form.
b. The only basis we have of knowledge of the external world is
through sense perception.
c. Sense perception, while fallible, is on the whole reliable because
the all powerful being who created us is no deceiver.
d. But this requires that we be very circumspect in relying on the
evidence of sense perception.
Specifically we must rely only on evidence which is exactly
specifiable (ideally in mathematical form), and invariant from
person to person and under varying conditions of perception
-- in short, impersonally given.
2. Natural science must therefore be very careful and discriminating of
how it relies on sense perception. As revealed through the method
of systematic doubt, sense perception is at best a representative
appearance, within the mind, of what is outside the mind.
a. Sense perception is conceived to be a product of the causal
impact of features of things in the external world upon the sense
organs of our body.
b. This impact produces two kinds of apparent features or qualities
in our sensory impressions:
i. Impressions which more or less accurately represent the
features of bodies in the external world ( = primary qualities), and
ii. Impressions which do not correspond but which are simply
produced in us as a result of the impact of these features on
our sense organs ( = secondary qualities).
c. Secondary qualities are conceived to vary from person to person
and underdifferent conditions of perception. This makes them
unreliableindicators of the true nature of things ( = subjective).
i. Examples include color, texture, warmth, meaning, value, and
purpose -- i.e., all qualitative features.
d. Primary qualities alone are conceived to be indicators of the true
nature of things( = objective), and they are what natural science
must solely relyupon.
ii. Examples include size, shape, mass, location, and motion -- i.e.,
all quantitative features of extension.
Western Oregon University
Copyright © 1997 Western Oregon University
Direct suggestions, comments, and questions about this page to Dale Cannon.
Last Modified 5/6/01