Cogito ergo sum

The Latin phrase Cogito ergo sum, or "I think, therefore I am", comes from the philosophy of Rene Descartes.

In his book Discourse on Method, Descartes attempted to build up an entire philosophical system from scratch. He began with the premise of doubting everything, but determined the one thing that a doubter could not doubt was his or her own existence. Thus the formulation, "I think, therefore I am", was the starting point of his philosophy.

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