philosophical truths in the way one proves a mathematical 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 more real 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.”