That was the question I was asked: how would you prove to a blind man, that photography exists?
I knew what he was getting at. We had been discussing psychics. He was a firm believer in psychic powers, had had psychic experiences, and regularly visited a psychic. His point was, since I had not experienced psychic powers, I would never be able to believe in what he ‘knew’ to be true. You could never prove to a blind man that photography exists, and likewise no one would ever be able to demonstrate to me that psychic powers were real.
It took me about ten seconds to think of a way to show he was wrong.