So how do we know anything at all, if in fact we know anything at all?
During the Middle Ages this question boiled down to whether divine revelation trumps reason as a source of human knowledge or vice versa.
A man stumbles into a deep well and plummets a hundred feet before grasping a spindly root, stopping his fall. His grip grows weaker and weaker, and in his desperation he cries out, "Is there anybody up there?"
He looks up, and all he can see is a circle of sky. Suddenly, the clouds part and a beam of bright light shines down on him. A deep voice thunders, "I, the Lord, am here. Let go of the root, and I will save you."
The man thinks for a moment and then yells, "Is there anybody else up there?"
-- From "Plato and a Platypus Walk Into a Bar: Understanding Philosophy Through Jokes"