Disagreement is an interesting phenomenon. Why do people disagree? When two people disagree, does that mean that neither person is right? Or, at the very least, should they recognize that the other person could be right? Should they both give up their beliefs? In this post, we’ll look at religious disagreement. Some skeptics argue that since people from different religions have different religious beliefs, we have reason to doubt that any religion is true. What can we say about this argument?
Equal Weight Theory
Believe it or not, there’s a well-developed theory in epistemology that argues that disagreement among epistemic peers is pretty good reason to doubt that a claim is true. Before we get into the argument, we first need to understand the term ‘epistemic peer.’ That will play a fairly large part in our assessment, so let’s get clear on what it means.
Imagine two twin brothers, James and John, that have both grown up to be excellent mathematicians. They’ve gone to the same schools, had the same teachers, and now teach at the same institution. They are peers in every respect. And imagine that they disagree on the outcome of some mathematical equation. Equal Weight Theory says that since James and John disagree, they are each forced to give up their own belief that their calculation is correct. Why? Because they are epistemic peers.
To get a little more formal, in “The Epistemic Significance of Disagreement,” Thomas Kelly says that two people are epistemic peers if they meet the following two conditions:
(ii) they are equals with respect to general epistemic virtues such as intelligence, thoughtfulness, and freedom from bias.
In our scenario, James and John meet (i) and (ii) above. So they are epistemic peers. But why should anyone think that mere disagreement between epistemic peers is reason to doubt? Let’s now turn to the argument from Equal Weight Theory.
Equal Weight Theory
Here is a standard formulation of the argument from Equal Weight Theory (EW):
(2) No such reason is available when the disagreeing parties are epistemic peers and have access to the same evidence.
(3) Therefore, one should give equal weight to the opinion of an epistemic peer and to one’s own opinion in cases of epistemic disagreement.
On the face of it, this seems like a pretty nice little argument. It’s difficult to see why we should reject the premises (if at all). I’ll admit that EW is at least initially plausible. There’s something to the argument.
EW and Religious Disagreement
Let’s now look at how EW can be used in an argument against Christianity.
(5) One should give equal weight to all the religious claims in (4) because they come from epistemic peers.
(6) Given (5), one should be agnostic about which religious claim is correct.
(7) So, belief in any particular religion is unjustified.
The argument above isn’t technically valid, but it could easily be made so. Don’t worry about that. It’s clear that premise (5) requires Equal Weight Theory. If EW is false, (5) is also false. Next we’ll look at two ways that reasonable Christians can respond to this argument.
I’ll quickly lay out two responses to this argument and then expound on them. The first response is to question the alleged epistemic symmetry between Christians and non-Christians. This response says that it’s actually unclear that non-Christians are our epistemic peers. The second response is to deny Equal Weight Theory altogether. (Note: you can be cool like me and deny both.) We’ll take each in turn.
Response 1: Denying Epistemic Peerhood
For reference, premise (4) states that all religious believers are epistemic peers. Christians, Muslims, Jews, etc. are all equal with respect to their familiarity of the evidence, they are equally free from bias, they are all equally thoughtful and intelligent, and so on. If we deny (4), we are saying that non-Christians aren’t like us with respect to all these virtues, that perhaps Christians have access to evidence non-Christians don’t, or some combination. Is this a viable option? Yes.
The Christian story involves the witness of the Holy Spirit. We Christians come to know the great truths of the Gospel through the work and testimony of the Holy Spirit. Non-believers reject this witness. So in very real way, if Christianity is true, then Christians and non-Christians don’t have access to the same kind of evidence. The Holy Spirit doesn’t force himself on non-believers. (There’s also the question of sin and its damages.) The upshot is that establishing epistemic peerhood between Christians and non-Christians requires establishing the falsehood of Christianity. That is no easy feat.
Maybe you think this is cheating. It’s too easy, perhaps even lazy, to appeal to characters in a Holy Book to save Christianity from failure. Fair enough–a few responses. First, the doctrine of the Holy Spirit has been around since the beginning of Christianity. This isn’t something being introduced to save Christianity–it’s more like a lesson in Christian theology. Second, appealing to the work of the Holy Spirit isn’t required to be skeptical of (4). It can be doubted for other reasons. For example, John DePoe has argued that, “due to the private nature of religious experiences (and their counterfeits), we are not able to compare the evidential quality of different supposed religious experiences.”
Moreover, epistemic symmetry is incredibly difficult to establish. Why think that any two religious people are perfectly symmetrical in every relevant epistemological way? Why think they are perfectly equally smart, that they have access to the same kind of evidence, or that one of them isn’t suffering a cognitive defect like confirmation bias? Moreover, a number of philosophers view intuitions (or seemings) as a kind of evidence. If that’s right, then clashing intuitions show that the two parties do not have access to the same evidence (otherwise they’d have identical intuitions). These questions are all very difficult to answer. Even a low bar of success for epistemic peerhood seems practically impossible to meet.
Being skeptical of (4) is a reasonable option for the Christian; it’s actually quite difficult to prove that any two people are epistemically symmetrical. 
Response 2: Denying Equal Weight Theory
Suppose you think, for whatever reason, that all religious believers are epistemic peers. There’s still an option here, which is to simply deny the thesis of Equal Weight Theory. For reference, that’s premise (5) in the above argument, which states that every religious claim must be given “equal weight.” Obviously, this premise doesn’t work unless we already accept that all religious believers are epistemic peers. For our purposes, we’ll assume that this is the case (even though that is far from obvious). How might we respond to the premise from Equal Weight Theory?
First we’ll look at some counterexamples to Equal Weight Theory. Most philosophers agree that the past is real. It wasn’t created 5 minutes ago with the appearance of age. But suppose that instead of this world, we lived in a different reality where philosophers were split on this question. In this world of make-believe, half of the philosophers believe the past is real, and the other half believe the past is not real. According to EW, the proper thing to do is to give up belief in the reality of the past. But is that reasonable? Many, including me, would say no.
But maybe you’re not convinced. Maybe these smart philosophers would have access to arguments that we haven’t considered (otherwise why would they be skeptical of the past?). But that’s an interesting point. It’s not the fact that people disagree that should cause us to doubt, but that there might be good arguments. Hence, doubt is really about the evidence, not about the existence of people that disagree. Let that sink in a second. It’s not the existence of people that disagree, but the existence of good arguments that should move us. This shows that EW is false.
Taking it a step further, suppose that some philosopher, call him Ben, is sitting isolated on an island somewhere thinking about the problem of evil. He is maximally informed on the argument–he knows all of the arguments for and all of the arguments against. And suppose he’s come to the conclusion that the problem of evil fails. But then, in our story, he learns that other philosophers outside of his island, that are just as informed as him, have reached the opposite conclusion. What should Ben do at this point? Well, it’s not as if he’s learned about some good argument for the problem of evil and that’s what’s causing him to doubt; Ben is maximally informed on the argument. So why should he doubt? Surely it can’t be the mere existence of philosophers that disagree.
Now, he might think that the fact other philosophers disagree is evidence that he has done a poor job in his assessment. But if that’s the case, then he should doubt his status as an epistemic peer. Alternatively, he might think it’s evidence that they, the other philosophers, have done a poor job in their assessment. In which case he should again doubt that these other philosophers are his epistemic peers with respect to the problem of evil. For Ben, determining which of these scenarios is true is nearly impossible. This is just more reason why epistemic symmetry is very difficult to prove.
We’ve come now to the strongest objection to EW which is that EW suffers from a kind of incoherence. Suppose instead of the problem of evil, Ben has been thinking about the truth of Equal Weight Theory. He’s analyzed the evidence for and against and has come out believing that EW is false (apparently, Ben is a smart guy). Now suppose he learns that another philosopher exists, call him Zach, that’s analyzed the same evidence and has come to the conclusion that EW is true. This fact (the fact of disagreement) shouldn’t move Ben at all. Why? He’s convinced EW is false. But interestingly, Zach is now forced to give up belief in EW. As a proponent of EW, Zach believes that disagreement among epistemic peers is reason to give up belief. So to be consistent, in light of Ben’s disagreement, Zach must now give up belief in EW.
But wait, couldn’t Zach just deny the epistemic peerhood of Ben? That’s right, he could! Let’s say he does that. Zach, a committed Equal Weight Theorist, denies that anyone that disagrees with him about EW is an epistemic peer, including Ben. But, and here’s where it gets really interesting, Ben disagrees. Ben is convinced that he and Zach are epistemic peers. But now we have more disagreement! What can Zach do at this point? Well, since he still endorses EW, to remain consistent, Zach must give up belief that Ben is not an epistemic peer. This option no longer being available to Zach implies that he must lessen his credence in EW or give it up altogether. 
Note that Ben’s position is unaffected by all this since he rejects EW. It follows that belief in EW suffers a kind of incoherence that nonbelief doesn’t. So long as there is disagreement about the truth of EW and the epistemic peerhood of two given people, one’s confidence in EW can’t be very high.  This is one of the strongest reasons to reject the argument. 
In this post we’ve looked closely at an argument against Christianity from religious disagreement. We saw that a particular version of the argument is based on Equal Weight Theory, the idea that disagreement among epistemic peers is reason to doubt that a claim is true. We then looked at two responses to the argument. The first was to deny epistemic peerhood between Christians and non-Christians. The second was to deny Equal Weight Theory altogether. I argued that both are reasonable options for Christians.
Here’s a challenge to the reader: think about the problem of religious diversity and ask yourself whether the version you are imagining depends on something like Equal Weight Theory. If it does, then this post does a lot of damage to that argument. If it doesn’t, please leave a comment–I’d love to take a look at it! 
I’m not convinced epistemic peers MUST give up their beliefs even if they are epistemic peers. For example, if we can show how one of our epistemic peers is mistaken in some way, then we have an undefeated reason to keep our belief.
I’m no proponent to the equal weights view, but it does seem that to maintain a proper degree of intellectual virtue one must suspend belief of lines view in order to listen to the opposing argument with proper open-mindedness?