I’m an evidentialist: I believe that that which is rational to believe is that which is justified by reason and evidence*. Justifications can't be infinite; they are ultimately founded upon that which we can perceive and remember. I don’t think that all of our perceptions and memories are reliable, but considering all of the exceptions is neither in scope nor required. For today, all that one must understand about my epistemology is that perception and memory can be directly justified (aka properly basic).
Here's a simple and familiar example of what I mean. I look at the kitchen table and see two boxes on it. The belief that there are two boxes on the table is directly justified by my seeing them. When I say that that belief is directly justified, I mean that I don't ordinarily need any additional evidence to know that there are a couple of boxes on the table; my perception is enough. I bet that you, like pretty much all humans, form rational beliefs like this all the time.
Now, I have to be open to information that could change my mind about that belief. Perhaps there is one box on the table and a mirror that makes it look like there is a second one, too. Upon learning that that that was the case, I’d have a defeater for my belief that would force me to change my mind. Quite simply, reason dictates that it's not possible to rationally hold both beliefs: (1) that there are two boxes on the table and (2) that there is one box plus a mirror that merely makes it look like there are two. But barring any such tricks or problems with my vision, I can know that there are two boxes on the table without needing any additional evidence or information. That belief can then serve as evidence for subsequent beliefs. If my son tells me that he was alone playing with some toy boxes in the kitchen a few seconds ago**, I can conclude with the rational belief that he probably left them there, and so on. Our perceptions can be directly justified and serve as foundations for rationally held beliefs.
But Johnston thinks that there is more to be perceived than that of which we normally think when we consider the familiar human senses of vision, hearing, vibration, temperature, etc. Johnston thinks that we can also include alongside those perceptions a way to perceive God and/or the Holy Spirit commonly known as revelation. In his words:
"All epistemology is based upon faith: the skeptic has faith in reason and perception; the theist has faith in revelation and reason . . . While the skeptic believes that perception is the only reliable source of data for his reason to consider, the theist does not say that it is only the senses which supply reliable data. Paul of Tarsus writes, "Eye has not seen nor has ear heard the wonders God has in store for those who love him." As I have suggested before, it is just as "rational" to accept sources of data other than the senses as it is not to accept them . . . There are many realms of knowledge, each with its own standard of proof. Science uses observation & the empirical guided by reason; law uses evidence (including witnesses) guided by reason; history uses the record guided by reason; theology uses revelation guided by reason."
I think that Johnston has work to do to make the case that revelation can be directly justified the way that other sense perception can, but I haven’t made the case that sensory perception can be directly justified today, and I’m not going to get into it at this moment (though this paper by Christian philosopher, James Sennett, is the bomb), so it would be unfair of me to demand that Johnston do so now. Rather, for the sake of argument, I’m going to accept that he may be right about that. It’s equally fine if Johnston thinks that accepting revelation is merely a matter of faith, as he has suggested. What’s important is that we both accept reason, as he admitted above. Remember that reason provides us with an epistemic duty to reject a belief when a defeater for that belief is identified. I intend to present a defeater based on reason for Johnston’s claim that revelation can lead to directly justified beliefs.
Let’s return to those boxes on the kitchen table, a belief that was, for me, directly justified by visual perception. Now imagine that you look at the table and see three boxes, instead. What if three others say that they see four, five, and six boxes on the table, and two others see none at all? There are no smoke and mirrors operative, and all seven of us are healthy, neurologically normal human beings.
Breathe this thought experiment deeply in and really imagine that you look and see three boxes. What are you going to conclude? Do you believe what your eyes are telling you, knowing what I and the others are or aren’t seeing? Or do you have enough doubt about your initial belief as to lead you to reject it and concede that something fishy is going on, something fishy enough to require you to refrain from making any rational claims about what’s actually on the table?
It seems rather obvious to me that it would be the height of arrogance to insist, against the knowledge of what one’s epistemic peers are perceiving differently, that what one, personally, is perceiving, forms a rational belief.
What if the person seeing six boxes says that she prefers a world where there are six boxes on the table because she needs them in which to wrap six presents. Do preferences or conveniences make beliefs rational?
The humble thing to do in this situation is the rational thing to do, and that is to recognize that something about this situation is undermining the ability to perceive what’s on the table. None of us seven people can, without additional evidence or reason, rationally form any beliefs about how many boxes are on the table let alone whether any boxes are on the table at all.
Notice that I’m not saying that your perception of three boxes is false. (I'm not making a de facto objection). You may be the right one among us. The two who see none may be right. Or maybe none of us is right. I’m saying that forming a rational belief about what's on the table based upon our vision isn't even possible. (I'm making a de jure objection).
And so it is with revelation. People born in India or Iran are Johnston’s epistemic peers, yet they almost exclusively have and/or believe in revelations about multiple gods in the former country and a different but no less mutually exclusive god in the latter. If you were an ancient Greek, you might well have had a theophany of Zeus or Apollo. And what about me and countless others like me? I was once a Christian who tried, genuinely tried, yet my "relationship with god was always a one-way street. I’ve never had any inkling of any revelation of any god, whatsoever^.
What must Johnston conclude about this state of affairs? Is it epistemically acceptable for him to claim that belief founded upon revelation is rational? Can Johnston successfully argue that he and certain other Christians are somehow epistemically superior to the rest of humanity without resorting to special pleading?
One thing that Johnston can't do is ignore this defeater by claiming that it's based upon a disanalogy in that the truth regarding how many (if any) boxes are on a table is normally amenable to an examination of empirical evidence while the truth regarding revelation and God are not. Why not? First, there is no disanalogy: the reason that the 7 observers are in trouble is that there is no way to answer their question with empirical evidence because none is available to them. They're stuck that way, just as are those who claim vastly different and mutually exclusive revelations. Second, that objection is about evidence, but the defeater posed by the analogy is entirely about reason.
Isn't it time for Johnston to admit that his belief in revelation, and Christian revelation in particular, is irrational? Claiming that these beliefs are based on faith doesn't somehow solve that problem; it's synonymous with it. Alternatively, he must defeat the rationality defeater I have presented, or provide other evidence or argumentation indicating why revelation is rational and true.
But I don't see how he can.
*Please notice that I'm not just talking about scientific evidence, here. The kind of evidence a historian might accept, or a judge in a court of law, are both included in evidentialism, where the strength of the belief is apportioned to the strength of the relevant evidence. Accordingly, my epistemology does not amount to scientism.
**I'm actually quite sympathetic to the idea that testimony can also be directly justified in certain situations, just as sense perception can.
^A reminder is required here: I don't conclude on that basis that revelation isn't rational or that god probably doesn't exist.