[Music] What am I? A thinking thing, that's what René Descartes believed. But how did he get there?
Descartes asked, "What, if anything, can I know for certain? " He decided he couldn't rely on any evidence acquired from his senses, since they sometimes misled him. A straight stick can look bent in water.
In the past, he'd mistaken the shape of objects in the distance and so on. Worse still, whilst sleeping, he sometimes dreamt he'd woken up. So how, then, could he be sure he wasn't dreaming now?
But hang on, surely 2 + 3 equals 5, even in a dream. Descartes, a mathematician, wouldn't get that wrong, would he? Even here, Descartes realized he couldn't claim absolute certainty; for what if an evil demon was in control of his thoughts, manipulating them so that every time he added numbers together, he made a basic error?
Where would that leave him? There would be nothing he could be sure of—just a whirlpool of doubt. Descartes' life belt was the realization that even if such a demon existed, it couldn't deceive him about his own existence.
Every thought, no matter how unreliable, proved he existed as a thinking thing. He could be more sure of that even than that he had a body. This is his famous cogito argument: "I think, therefore I am.
" Cogito ergo sum.
