Descartes reasoning in a nutshell

rene descartes

“Descartes maintains that we cannot accept anything as being true unless we can clearly and
distinctly perceive it. To achieve this can require the breaking down of a compound problem into as
many single factors as possible. Then we can take our point of departure in the simplest idea of all.
You could say that every single thought must be weighed and measured, rather in the way Galileo
wanted everything to be measured and everything immeasurable to be made measurable. Descartes
believed that philosophy should go from the simple to the complex. Only then would it be possible to
construct a new insight. And finally it would be necessary to ensure by constant enumeration and
control that nothing was left out. Then, a philosophical conclusion would be within reach.”
“It sounds almost like a math test.”
“Yes. Descartes was a mathematician; he is considered the father of analytical geometry, and he
made important contributions to the science of algebra. Descartes wanted to use the ‘mathematical
method’ even for philosophizing. He set out to prove philosophical truths in the way one proves amathematical theorem. In other words, he wanted to use exactly the same instrument that we use when
we work with figures, namely, reason, since only reason can give us certainty. It is far from certain
that we can rely on our senses. We have already noted Descartes’s affinity with Plato, who also
observed that mathematics and numerical ratio give us more certainty than the evidence of our
senses.”
“But can one solve philosophical problems that way?”
“We had better go back to Descartes’s own reasoning. His aim is to reach certainty about the nature
of life, and he starts by maintaining that at first one should doubt everything. He didn’t want to build
on sand, you see.”
“No, because if the foundations give way, the whole house collapses.”
“As you so neatly put it, my child. Now, Descartes did not think it reasonable to doubt everything,
but he thought it was possible in principle to doubt everything. For one thing, it is by no means certain
that we advance our philosophical quest by reading Plato or Aristotle. It may increase our knowledge
of history but not of the world. It was important for Descartes to rid himself of all handed down, or
received, learning before beginning his own philosophical construction.”
“He wanted to clear all the rubble off the site before starting to build his new house ...”
“Thank you. He wanted to use only fresh new materials in order to be sure that his new thought
construction would hold. But Descartes’s doubts went even deeper. We cannot even trust what our
senses tell us, he said. Maybe they are deceiving us.”
“How come?”
“When we dream, we feel we are experiencing reality. What separates our waking feelings from
our dream feelings?
“ ‘When I consider this carefully, I find not a single property which with certainty separates the
waking state from the dream,’ writes Descartes. And he goes on: ‘How can you be certain that your
whole life is not a dream?’ “
“Jeppe thought he had only been dreaming when he had slept in the Baron’s bed.”
“And when he was lying in the Baron’s bed, he thought his life as a poor peasant was only a dream.
So in the same way, Descartes ends up doubting absolutely everything. Many philosophers before him
had reached the end of the road at that very point.”
“So they didn’t get very far.”
“But Descartes tried to work forward from this zero point. He doubted everything, and that was the
only thing he was certain of. But now something struck him: one thing had to be true, and that was that
he doubted. When he doubted, he had to be thinking, and because he was thinking, it had to be certain
that he was a thinking being. Or, as he himself expressed it: Cogito, ergo sum.”
“Which means?”
“I think, therefore I am.”
“I’m not surprised he realized that.”
“Fair enough. But notice the intuitive certainty with which he suddenly perceives himself as a
thinking being. Perhaps you now recall what Plato said, that what we grasp with our reason is morereal than what we grasp with our senses. That’s the way it was for Descartes. He perceived not only
that he was a thinking /, he realized at the same time that this thinking / was more real than the
material world which we perceive with our senses. And he went on. He was by no means through
with his philosophical quest.”
“What came next?”
“Descartes now asked himself if there was anything more he could perceive with the same intuitive
certainty.
He came to the conclusion that in his mind he had a clear and distinct idea of a perfect entity. This
was an idea he had always had, and it was thus self-evident to Descartes that such an idea could not
possibly have come from himself. The idea of a perfect entity cannot have originated from one who
was himself imperfect, he claimed. Therefore the idea of a perfect entity must have originated from
that perfect entity itself, or in other words, from God. That God exists was therefore just as self-
evident for Descartes as that a thinking being must exist.”
“Now he was jumping to a conclusion. He was more cautious to begin with.”
“You’re right. Many people have called that his weak spot. But you say ‘conclusion.’ Actually it
was not a question of proof. Descartes only meant that we all possess the idea of a perfect entity, and
that inherent in that idea is the fact that this perfect entity must exist. Because a perfect entity wouldn’t
be perfect if it didn’t exist. Neither would we possess the idea of a perfect entity if there were no
perfect entity. For we are imperfect, so the idea of perfection cannot come from us. According to
Descartes, the idea of God is innate, it is stamped on us from birth ‘like the artisan’s mark stamped on
his product.’ “
“Yes, but just because I possess the idea of a crocophant doesn’t mean that the crocophant exists.”
“Descartes would have said that it is not inherent in the concept of a crocophant that it exists. On
the other hand, it is inherent in the concept of a perfect entity that such an entity exists. According to
Descartes, this is just as certain as it is inherent in the idea of a circle that all points of the circle are
equidistant from the center. You cannot have a circle that does not conform to this law. Nor can you
have a perfect entity that lacks its most important property, namely, existence.”
“That’s an odd way of thinking.”
“It is a decidedly rationalistic way of thinking. Descartes believed like Socrates and Plato that
there is a connection between reason and being. The more self-evident a thing is to one’s reason, the
more certain it is that it exists.”
“So far he has gotten to the fact that he is a thinking person and that there exists a perfect entity.”