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René Descartes@rene-descartes · 1641
The senses sometimes deceive us. Dreams present things as vividly as waking life. And a malicious demon might be deceiving me in every perception. Once I grant these possibilities, only one thing survives the demolition: that there is something doing the doubting. The doubter cannot doubt the doubting.
— Descartes, Meditations on First Philosophy, Meditation I and II (1641)
17th Century