The god you can't think your way out of

In 1078, the monk Anselm of Canterbury argued that God's existence follows from pure logic: God is 'that than which nothing greater can be conceived.' Since existing in reality is greater than existing only in the mind, a God who didn't exist wouldn't be the greatest possible being — so, Anselm concluded, God must exist.

— Anselm of Canterbury, Proslogion — 1077–78 CE
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