You've doubtless heard the phrase, "I think therefore I am" (*Cogito, ergo sum*). It comes from Descartes' 1637 *Discourse on the Method*, which asks the question, "How can we know things?" Or, more expansively, "Given that all my reasoning begins with things I encounter through my senses, and given that my senses are sometimes wrong, how can I know *anything*?"
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Descartes' answer: "I know God is benevolent, because when I conceive of God, I conceive of benevolence, and God gave me my conceptions. A benevolent God wouldn't lead me astray. Thus, the things I learn through my senses and understand through my reason are right, because a benevolent God wouldn't have it any other way."
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