What of the soul, then? An explanation was required not least of how something 'spiritual' could start a mechanical process."
"It's a strange thought, actually."
"What is?"
"I decide to lift my arm--and then, well, the arm lifts itself. Or I decide to run for a bus, and the next second my legs are moving. Or I'm thinking about something sad, and suddenly I'm crying. So there must be some mysterious connection between body and consciousness."
"That was exactly the problem that set Descartes's thoughts going. Like Plato, he was convinced that there was a sharp division between 'spirit' and 'matter.' But as to how the mind influences the body--or the soul the body--Plato could not provide an answer."
"Neither have I, so I am looking forward to hearing what Descartes's theory was."|Q墨-shu-蠅ang|
"Let us follow his own line of reasoning."
Albert pointed to the book that lay on the table between them.
"In his Discourse on Method, Descartes raises the question of the method the philosopher must use to solve a philosophical problem. Science already had its new method..."
"So you said."
"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 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?"