4. “I think therefore I am” – René Descartes (1596 – 1650) Descartes [wiki] began his philosophy by doubting everything in order to figure out what he could know with absolute certainty. Although he could be wrong about what he was thinking, that he was thinking was undeniable. Upon the recognition that “I think,” Descartes concluded that “I am.” On the heels of believing in himself, Descartes asked, What am I? His answer: a thinking thing (res cogitans) as opposed to a physical thing extended in three-dimensional space (res extensa). So, based on this line, Descartes knew he existed, though he wasn’t sure if he had a body. It’s a philosophical cliff-hanger; you’ll have to read Meditations to find out how it ends.
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