Kevin Vallier has a couple of posts (here and here) at Bleeding Heart Libertarians in which he attempts to establish that beliefs held by Christians are, at the minimum, reasonable. You can find some of my objections in the comments of those posts, but I thought I might take the time to discuss the idea here.

To what extent is any set of beliefs "reasonable?" Vallier lays out two criteria: (1) The belief has "epistemic credence," and (2) the belief is sufficiently rational to influence action. Let's take a brief look at what he means.

Regarding the first point, all Vallier really means is that the belief can be justified somehow. "Justification" is, itself, its own sub-discipline within philosophy, and not one with which I am overly familiar with. Thus, a full treatment of the justification problem is out-of-scope for this post, but the important thing is simply that justifications exist in support of Christianity, namely: authoritative testimony, historical account, and feelings. This doesn't mean any of these things are sufficient to win over anyone considering the merits of Christianity, it simply means that a believer has the ability to justify his belief to himself.

I note that this is a rather weak standard of "reasonableness," but it is what it is.

Regarding the second point, what Vallier means is something like this: I might believe that there are aliens living on one of Neptune's moons, intelligent lifeforms that have a rich society and culture, but who will never, ever have the technological means to make contact with people on Earth. I might even be able to develop an internally consistent justification for this belief. However, nothing about this belief will ever influence anything I do on Earth.

This second point is Vallier's weaker point, I think, since physicists often theorize about the physical conditions in and around black holes. These theories will never influence the actions of any physicist or layman here on the surface of the Earth, but they are still reasonable beliefs because they conform to our current knowledge of the universe.

Given the weakness of this second point, I think we can set it aside.

For my part, I think it is safe to say that any belief can be justified somehow. The question of reasonableness seldom comes down to whether or not a belief can be justified, but more specifically whether it can be justified in light of all the knowledge held by the believer.

In other words, I might be able to justify a belief in reincarnation, but how easily can I justify a belief in reincarnation in light of what I know about physics? How easily can I justify a belief in the Holy Trinity in light of a complete dearth of physical evidence for any sort of supreme being, much less one that has somehow managed to split himself into three equal parts that interact with human beings differently?

I guess what I'm trying to say is that justification is not a sufficient condition for reasonableness. Clinging to justifications that ultimately fail to satisfy our epistemological integrity is what illusions are all about. At a certain point, one has to draw a line. One has to come to a point where they can no longer tolerate the sound of their own bad rationalizations.

Plenty of smart, reasonable people believe in Christianity. Christianity is not really the point here. The point is that anything is reasonable if we use Vallier's definition of reasonable. That suggests to me that his definition is a bad one.