Recently I wrote about "Five criteria for a 'God Theory' that religions fail." One of philosopher L.R. Hamelin's criteria related to private knowledge.
If her theory can be tested only by private revelation, not by observations available to everyone, she unjustifiably claims private knowledge.
Someone left a comment on this post, wondering why private knowledge wasn't justifiable. This was my reply:
Here's how I see the issue of "private revelation" and "private knowledge."
Can knowledge be private? Only if we define knowledge in a way that makes it virtually (or completely) synonymous with subjective experience. But then it isn't really knowledge -- something that holds true for more than just a single experiencer.
I feel uplifted when I gaze upon a rushing mountain river in early morning sunlight. (Just did that half an hour ago, actually.) That experience happened to me. But can I call this "knowledge" and expect others to accept it as such?
Well, they can trust that I did indeed have that experience. But there's no way that I, or anyone else, can prove that I really did. Even brain scanners, if one could be hooked up to me on the riverbank, could only show broadly what is happening in my brain, not the experiential feeling associated with this.
So I think the author of that quote was claiming something defensible: a private experience is unjustifiably claimed as private knowledge. Meaning, a person's subjective experience can't be held out as actual knowledge of some objectively real aspect of the world without evidence that is more than private.
Otherwise, what are we left with? Anyone could claim anything to be true, demanding that others accept it as true. I get pulled over by a policeman for speeding. I tell him "God told me that I needed to go that fast, so speeding is part of my religious freedom." He or she should laugh at me.
Yes, satsangis and other religious believers make claims to private knowledge. All the time. So does everyone else. Whenever I say "I feel..." or "I dreamed..." I'm claiming private knowledge. But like I said, this really is a claim to a private experience, which isn't objectionable.
I can accept that you had a private experience, because I assume you have subjectivity, just as I do. However, if you want me to accept your private experience as something true about the world, you need to bring forth more than just a subjective claim.
Reading on in the book the "private knowledge" reference came from -- Jerry Coyne's "Faith vs. Fact: Why Science and Religion are Incompatible" -- I've found some passages that echo what I said.
What is true may exist without being recognized, but once it is it becomes knowledge. Similarly, knowledge isn't knowledge unless it is factual, so "private knowledge" that comes through revelation or intuition isn't really knowledge, for it's missing the crucial ingredient of verification and consensus.
..."I'm hungry," my friend tells me, and that too is seen as extrascientific knowledge. And indeed, any feeling that you have, any notion or revelation, can be seen as subjective truth or knowledge. What that means is that it's true that you feel that way.
What that doesn't mean is that the epistemic content of your feeling is true. That requires independent verification by others. Often someone claiming hunger actually eats very little, giving rise to the bromide "Your eyes are bigger than your stomach."
...As William James argued, it is the subjective and revelatory aspects of religion that gives it the most purchase: the feeling of certainty that religious claims are true. But when one has a religious experience, what is "true" is only that one has had that experience, not that its contents convey anything about reality.
To determine that, one needs a way to verify the contents of a revelation, and that means science. After all, while some Christians accept the existence of Jesus because they have mental conversations with him, Hindus have mental conversations with Shiva, and Muslims with Allah.
...I've argued that science, construed broadly as a commitment to the use of rationality, empirical observation, testability, and falsifiability, is indeed the only way to gain objective knowledge (as opposed to subjective knowledge) about the universe.