The Rationalist Approach of René Descartes The medieval world into which René Descartes was born in 1596 was beginning to come apart. The great synthesis that had held knowledge together under the control of the Church and the authority of Aristotle was unraveling, and many things that had seemed settled or obvious were being questioned. The stable if somewhat stifling world of his childhood—in which the Church was the keeper of all knowledge and books were written in Latin, thereby limiting access to knowledge to scholars and churchmen—had been jolted by the scientific revolution.    When he was in his twenties, Descartes had a kind of intellectual crisis. Taking seriously the questions we have been considering, he began to wonder whether there was anything in his mind that he could know with certainty. The Use of Methodic Doubt to Examine Knowledge When Descartes began his search for certain knowledge, he decided to doubt everything systematically and see whether anything remained after this process. Any knowledge that was left would have, by surviving such a test, achieved the status of certainty. Much of what he found in his mind seemed to have arrived there on the authority of someone else; he had been told many things and read others, without questioning the authority of the source. In other words, like most of us, he accepted as facts both things his teachers told him and things he read in books. He had no independent verification for this apparent knowledge; he had only the word or the authority of the source as assurance that what he thought was true was indeed true.    What about the senses? Could they be relied upon to provide knowledge? To test the reliability of his senses, Descartes took a piece of beeswax and heated it in a candle flame, watching every property of the wax change before his eyes: · Let us take, for example, this bit of wax which has just been taken from the hive. It has not yet completely lost the sweetness of the honey it contained; it still retains something of the odor of the hive from which it was collected; its color, shape, and size are apparent; it is hard and cold; it can easily be touched; and, if you knock on it, it will give out some sound … But now while I am talking I bring it close to the fire. What remains of the taste evaporates; the odor vanishes; its color changes; its shape is lost; its size increases; it becomes liquid; it grows hot; one can hardly touch it; and although it is knocked upon it will give out no sound.7 If he were to use the evidence supplied by his senses, Descartes concluded, he would have to declare that the wax after being heated was completely different from the wax before being heated. To conclude that the wax retained its identity during this transformation, Descartes realized that he had relied on his understanding, not on his senses.    As the next step in his systematic process, Descartes applied methodic doubt to his ordinary perceptions of reality, comparing them w ...

1. The Rationalist Approach of René Descartes
The medieval world into which René Descartes was born in
1596 was beginning to come apart. The great synthesis that had
held knowledge together under the control of the Church and the
authority of Aristotle was unraveling, and many things that had
seemed settled or obvious were being questioned. The stable if
somewhat stifling world of his childhood—in which the Church
was the keeper of all knowledge and books were written in
Latin, thereby limiting access to knowledge to scholars and
churchmen—had been jolted by the scientific revolution.
When he was in his twenties, Descartes had a kind of
intellectual crisis. Taking seriously the questions we have been
considering, he began to wonder whether there was anything in
his mind that he could know with certainty.
The Use of Methodic Doubt to Examine Knowledge
When Descartes began his search for certain knowledge, he
decided to doubt everything systematically and see whether
anything remained after this process. Any knowledge that was
left would have, by surviving such a test, achieved the status of
certainty. Much of what he found in his mind seemed to have
arrived there on the authority of someone else; he had been told
many things and read others, without questioning the authority
of the source. In other words, like most of us, he accepted as
facts both things his teachers told him and things he read in
books. He had no independent verification for this apparent
knowledge; he had only the word or the authority of the source
as assurance that what he thought was true was indeed true.
What about the senses? Could they be relied upon to provide
knowledge? To test the reliability of his senses, Descartes took
a piece of beeswax and heated it in a candle flame, watching
every property of the wax change before his eyes:
· Let us take, for example, this bit of wax which has just been
taken from the hive. It has not yet completely lost the sweetness
of the honey it contained; it still retains something of the odor

2. of the hive from which it was collected; its color, shape, and
size are apparent; it is hard and cold; it can easily be touched;
and, if you knock on it, it will give out some sound … But now
while I am talking I bring it close to the fire. What remains of
the taste evaporates; the odor vanishes; its color changes; its
shape is lost; its size increases; it becomes liquid; it grows hot;
one can hardly touch it; and although it is knocked upon it will
give out no sound.7
If he were to use the evidence supplied by his senses, Descartes
concluded, he would have to declare that the wax after being
heated was completely different from the wax before being
heated. To conclude that the wax retained its identity during
this transformation, Descartes realized that he had relied on his
understanding, not on his senses.
As the next step in his systematic process, Descartes applied
methodic doubt to his ordinary perceptions of reality,
comparing them with dreams and finding no clear way to
distinguish between the two. In a very vivid dream, you are sure
the events are really happening to you—until you wake up; only
then can you look back and label as a dream the experience you
had. While it is going on, a very realistic dream is virtually
indistinguishable from waking reality. Although he was
convinced that he was sitting at his writing table before the fire,
Descartes realized that he had dreamed himself in this exact
situation. While the dream was going on, it had seemed just as
verifiable as ordinary reality.
THE MAKING OF A PHILOSOPHER
René Descartes
(1596–1650)
Born in Tours, France, into a prominent family, Descartes
received a classical education from the Jesuits and at age twenty
took a law degree from the University of Poitier. He joined the
Dutch army and later the army of Bavaria. Armies didn't fight
during the winter months, so he had time to think and write.
First, he used mathematics to solve problems of military
engineering and eventually invented analytic geometry. At the

3. age of twenty-three, he “discovered the foundations of a
wonderful science,” which was published as the Discourse on
Method in 1637. Descartes was a loyal Catholic who wanted to
be the Thomas Aquinas of his day, reconciling the teachings of
the Church with the new science as Thomas had done with
Aristotle. Invited to Sweden to instruct Queen Christina in
philosophy (she sent an ambassador and a warship to fetch him),
he caught pneumonia trudging through the snow at 5 a.m. and
was dead within two weeks.
To test this, think about how you would go about proving to
yourself or to someone else that you are not dreaming right
now. Chuang-tzu (399–285 b.c.e.), the Taoist philosopher, once
had an incredibly realistic dream in which he was a butterfly,
flying luxuriously from flower to flower and enjoying the
warmth of the Sun. When he “awoke” to find himself sitting
solidly on the earth and in his usual identity as a philosopher,
he asked himself this question: Am I a Chinese philosopher who
has dreamed himself a butterfly, or am I a butterfly who now
dreams himself to be a Chinese philosopher?
Another area of knowledge Descartes examined for possible
certainty was mathematics, a field in which he, as the inventor
of analytic geometry, was intellectually very comfortable.
Surely, 2 and 2 must always equal 4, right? Descartes felt just
as certain as you do that 2 and 2 do indeed add up to 4. He
assumed, as we do, that what seems logically certain is very
reliable as knowledge. What he questioned was the ultimate
foundation for our certainty. Suppose a very powerful but very
evil deity has amused himself or herself by making all of us
believe that 2 and 2 add up to 4 when they really add up to 5, or
to the square root of 10 or to anything other than 4. The fact
that we are all secure in our agreement that 2 plus 2 equals 4
does not make it so if such a malevolent superior being has
decided to confuse us. We really have no way of knowing that
this is not the case, so even the so-called truths of mathematics
must be doubted.
Descartes went to his favorite restaurant for dinner. After

4. recommending several good dishes, the Maitre d' said, “The
duck is really excellent, Monsieur Descartes, may I bring you
the duck this evening?”
After thinking for a moment, Descartes replied, “I think
not”—and disappeared.
Author unknown
Am I a Chinese philosopher dreaming I'm a butterfly or a
butterfly dreaming I'm a Chinese philosopher, and how can I
decide?
In applying this process of systematic or methodic doubting,
Descartes realized he was rapidly eliminating almost everything
he had previously thought of as “knowledge.” Finally, however,
he came to something he felt was impossible to doubt—
something, at last, of which he could be certain. In the
following famous passage, Descartes concludes that, without
doubt, he is doubting. If he is doubting, he is thinking and must
therefore exist as a thinking thing:
HOW PHILOSOPHY WORKS: Methodic Doubt (Zero-Based
Epistemology)
You may be familiar with a budget-building method called zero-
based budgeting. Instead of carrying everything in your present
budget forward into the next year and writing justifications only
for the new things you wish to add, zero-based budgeting starts
from zero. Every item must be justified. All the things you
spent money on in the current year must be rejustified, along
with any new expenditures you'd like to make next year.
Descartes does something like this with his method of doubt. He
is unwilling to assume anything in his mind to be true, so he
casts it all out by doubting in a systematic or methodic manner.
This is a kind of zero-based epistemology because he will allow
nothing into his mind as certain knowledge unless and until he
justifies it by deducing or reasoning its certainty. Once he
deduces the Cogito and admits his existence as a certainty, he
insists that every other item be similarly justified—God, the
material world, even his own body.

5. · Even though there may be a deceiver of some sort, very
powerful and very tricky, who bends all his efforts to keep me
perpetually deceived, there can be no slightest doubt that I
exist, since he deceives me; and let him deceive me as much as
he will, he can never make me be nothing as long as I think that
I am something. Thus, after having thought well on this matter,
and after examining all things with care, I must finally conclude
and maintain that this proposition: I am, I exist, is necessarily
true every time I pronounce it or conceive it in my mind.8
When the essence of this now famous proof was rendered in
Latin, the translation of “I think, therefore I am” became
“Cogito ergo sum.” As a result, this proof is known as the
Cogito.
With the Cogito, Descartes has finally arrived at certain
knowledge, but it is unfortunately very limited knowledge.
What Descartes can be sure of is only the contents of his own
mind. In philosophy this is called solipsism, the belief that only
minds and their contents exist. Even if Descartes can be sure he
exists as a thinking thing, he still cannot trust his perceptions
that he has a body and that there is a world outside his mind;
nor can he be sure that the mathematical certainties he has are
correct. In other words, he has reasoned himself into a very
small box.
We will begin our discussion of epistemology with Cartesian
rationalism. Rene Descartes (1596-1650) was a French
mathematician who agreed with Plato and the early theologians
about the importance of reason. However, he found that his
predecessors often established their ideas upon what he took to
be a somewhat shaky and uncertain foundation. Thus, he begins
his own project by recognizing that everything he thinks he
knows could be the result of sense experience (which can
deceive us, as when we think the road is wet when in fact it is
only a trick of light) or inherited ideas (which may be true, but
also have not been verified). In other words, Descartes begins

6. his project with the somewhat revolutionary idea that we may
not know anything at all with any certainty.
Thus, Descartes decides to strip away all of his beliefs until the
only ones that remain are the ones that absolutely cannot be
doubted. Once these core beliefs are established, he reasons that
he can build all future beliefs upon these bedrock pieces of
knowledge. To do this stripping away, he uses a series of
increasingly strong metaphysical doubts. We'll discuss what
happens to his pursuit of knowledge shortly, but for now, let’s
take a look at the system he came up with to guide his inquiry:
the Cartesian Method
Discourse on Method presents the four precepts that
characterize the Cartesian Method:
1. Never accept anything as true anything that can be doubted.
Even a remote doubt is sufficient to require that a
belief/assertion be examined.
2. Divide ideas/beliefs about which one is uncertain into as
many parts as possible (i.e., divide and conquer)
3. Proceed to examine each section of knowledge/belief step-by-
step, even if these beliefs/ideas are not generally considered to
follow from one another.
4. Be exhaustive! Review all beliefs for clarity and coherence.
HisMeditations on First Philosophy details his system in action.
In this text, he claims to establish not only that he exists but,
also that God exists! Let’s see how he attempts to accomplish
this.
In Meditation One, “Concerning Those Things That Can Be
Called into Doubt,” Descartes begins by proclaiming that he is
going to question everything he knows by questioning the
founding principles of his beliefs. The first belief he doubts is
that in the infallibility of his senses. He is worried that life
could be a dream or, worse, a deception put on by an evil god.
Of course, Descartes claims to be a man of faith, and the
Christian God in whom Descartes believes would never deceive
him in this way. Still, he is questioning all his beliefs, including
those based on faith. Thus, his next step is to suppose the worst:

7. What if God is the opposite of what I am inclined to believe,
and he created life such that it is an illusion that I buy
wholeheartedly as reality? This might mean that I have no body,
and that the world as I know it does not exist. (This is similar to
what the cave dweller in Plato’s Republic realizes when he
leaves the cave, but even more extreme: Descartes is
entertaining the notion that not only might we be wrong about
the nature of ourselves and what we perceive to be real, but we
may not exist at all!)