Philosophy
Anselm's Ontological Argument for God's Existence
Quick fact
Anselm first formulated this argument in 1078 in his work Proslogion, and it has been debated by philosophers such as Thomas Aquinas, René Descartes, Immanuel Kant, and Alvin Plantinga.
Why this is interesting
What if you could prove the existence of the most perfect being simply by thinking about it—without looking at the world at all?