[this essay first appeared as comments to "Dude, where's my god?"]
A Deacon by the grace of God offers a phenomenalistic account of theism. This account, however, seems both a rational non-starter as well as unacceptably naive in itself.
Let me first accept arguendo that he has had some sort of valid subjective experience of the mystery of God.
Even so, you just can't go anywhere, at least not rationally, from such an experience: The experience is an experience of mystery. By definition, a mystery is unknown. You might get a warm fuzzy feeling, but you can't reason from a mystery to anything.
To actually reason from your experiences, your experiences have to be, at some level, non-mysterious.
He can't even put the mystery itself into words. As an engineer, I'm appalled at his abuse of language in asserting that God does not exist but that God is. I'm forgiving, though: Rather than analytical, such an assertion seems koanic, and I like koans. The only way to discuss a mystery is to assert an (apparent?) contradiction.
To get to any sort of substantive theology, however, to relate your deistic experiences to your other, prosaic, experiences, you're going to have to make some assertions about your non-mysterious experiences.
I'd like to see those non-mysterious experiences explicitly asserted, rather than slipped in as enthymemes.
About the subjective experiences themselves.
It is (to me) unproblematically rational that we reason from our subjective experiences to knowledge about objective reality. Rationality comprises—in my view—not just logic but also sensibility: agreement with our actual experience. I'm of a scientific mind, and (shared) experience is the foundation of science. Popper asserts, and I agree, that whatever we can say about science (being easier to discuss because science restricts itself to the investigation of public, intersubjective experiences) also applies to phenomenalism, the construction of our private notions about reality on the basis of our private subjective experiences. The scientific method is literally one-to-one transferable from public facts to private facts.
So, I'll grant the mode of reasoning. I'll argue, however, that the phenomenology of religion does not use that mode correctly: It does not use that mode scientifically.
There are two critical and difficult tasks in applying the scientific method: Accepting the facts as facts (in phenomenalism one's experiences as experiences), and then reasoning to an ontological interpretation.
These tasks are difficult because it is well-established in cognitive science, and well-understood by artists, detectives, scientists and maintenance engineers that one's non-conscious (preconscious and subconscious) mind does not supply one's conscious mind with "raw" experience from which we consciously draw conclusions about objective reality.
Our non-conscious minds, rather, supply us with a naive ontological interpretation of our "raw" experiential data. We must apply conscious discipline to strip away the naive non-conscious ontological interpretation to get at the facts or experiences as experiences. Only then, when one has "seen clearly", can one even begin to apply conscious reason to one's experiences.
Of course, our naive ontology, honed by half a billion years of evolution, works well under ordinary circumstances: Just because an ontological interpretation is naive doesn't necessarily mean it's wrong. But as soon as we get even a little bit away from ordinary circumstance—even to the extent of observing a pencil apparently bent by refraction—our naive ontology becomes suspect.
Every substantial scientific advance has come from a scientist identifying and stripping away the naive ontology of some phenomenon, and seeing the phenomenon for itself. After that, reasoning to a better conscious ontological interpretation, while still difficult, becomes possible.
So yes, I'll grant in theory that subjective experiences possibly could justify belief in God. But it is not enough to simply assert, "I've experienced the mystery of God." The inclusion of a naive ontology in such a statement seems blatantly obvious to me. I'm not challenging, the experience, nor the idea one that can reason from your experience to the truth; I'm arguing, rather, that the standard religious interpretation of those experiences is unacceptably naive.