The Blind Man and the Moon
A parable:
There were two men walking after sunset. One of them could see, and the other was blind.
The seeing man looked up to the sky and said “The Moon is very beautiful tonight.”
The blind man responded “Moon? What moon? Show me the moon. How do you know that there is a moon?”
The seeing man replied “Well I can see the moon.”
“That’s no good to me” said the blind man. “If it’s a matter of seeing then I can only take your word for it. Perhaps you are lying, or hallucinating. I want to have evidence before I believe in a moon. Real solid evidence.”
“Like what?” said the seeing man.
“Perhaps I could hear the moon?”
“No,” said the seeing man, “the moon is always silent.”
“Then perhaps I could touch the moon, or smell it or taste it?”
“No,” said the seeing man, “I don’t see how you could.”
At the end of this, they were left with a strange situation. Both of them were being reasonable; both of them refused to believe in a moon until they had examined the evidence. But the evidence came only in the form of sight, which only one of them could sense. Thus it was that two logical people came to opposite conclusions about the same subject.
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The parable illustrates something I call Noncommunicable Evidence. It is evidence which is available to one party, which is not available (or at least not directly available) to another.
Note that a person who claims access to Noncommunicable Evidence does not necessarily have such access. The one who claims to “see” may actually be blind, even if he believes his own claims. For instance, various people have claimed to have direct knowledge of the will of some God, claiming “God desires X”, despite the fact that other people also claimed such knowledge, claiming “God does not desire X”. Obviously someone has it wrong. (And of course there are others, such as myself, who don’t believe in any divine or spiritual knowledge to begin with, except as metaphorical concepts.)
Nevertheless, remember that not everyone has access to the same evidence at all times.