Here are three quotes from Adam Elga’s paper Reflection and Disagreement, which I think are broadly indicative of how Adam intends to understand the Equal Weight View of disagreement.
When you count an advisor as an epistemic peer, you should give her conclusions the same weight as your own.
[T]he equal-weight view entails that one should weigh equally the opinions of those one counts as peers, even if there are many such people.
It [i.e., the Equal Weight View] says that one should defer to an advisor in proportion to one’s prior conditional probability that the advisor would be correct.
Let’s focus on the last of these, though I think you can make the same point about all of the quotes. Consider the following situation.
Prior to thinking about a question, S thinks it is just as likely that she and T, her peer, will come to the right answer. S gets evidence E, and considers whether p. She concludes that p is indeed true. Her friend T reaches the same conclusion, on the same evidence. This is a horrible mistake on both their parts. The evidence in fact strongly supports ¬p, and p is indeed false. Given the Equal Weight View, what should S do?
A literal reading of the last quote says that she should believe p. After all, there are two people, S and T, and her prior judgment was that each of them was equally likely to be right. So she should ‘defer’ to the average position between the two of them. But since they agree, that means she should do what they both say, i.e. believe p.
But this seems crazy. It was, by hypothesis, irrational for S to believe p on the basis of E in the first place. A literal-minded reading of the Equal Weight View suggests that she can ‘launder’ her irrational beliefs, and have them come out as something she should believe, by simply considering herself an advisor.
Let’s note an even stranger consequence of this way of taking the Equal Weight View. Assume S finds out that T did not in fact make this judgment. That’s because T simply hasn’t considered the question of whether p is true. The only one of her ‘peers’ who has considered that question, on the basis of E, is S herself. Again, a literal minded reading of the Equal Weight View suggests that she now should believe what she actually believes. But that’s wrong; her belief is both false and irrational, and she shouldn’t hold it.
I actually don’t think this is a deep problem for the Equal Weight View. As my repeated references to ‘a literal-minded reading’ of the view have suggested, it seems that the objection here is based on a misinterpretation of what was intended. But I think it’s interesting to note for two reasons. One is that the misinterpretation isn’t so bizarre that it shouldn’t be expressly addressed by proponents of the Equal Weight View. The other is that it isn’t obvious what the right interpretation is. I can think of two very different ways out of the problem here.
One way out, the one I suggest for proponents of the Equal Weight View in Do Judgments Screen Evidence, is to restrict the principle to agents who are making rational decisions. The Equal Weight View then doesn’t have anything to say about agents who start making an irrational decision themselves.
The other way out is to stress an analogy with other modals in consequents of conditionals. So Humeans sometimes say things like “If you desire an end, you should desire the means to it.” That sounds false in some cases. If I desire to rob a bank, I shouldn’t desire the means to rob a bank – I should change my desires. But there presumably is a true reading of the means-end conditional.
One way to make that conditional true is to take the ‘should’ to have wide scope, and read the conditional as “You should make this conditional true: if you desire the end, you desire the means.” Perhaps the Equal Weight View is best framed the following way. You should make this conditional true: “If the average of your peers’ judgment is J, your judgment is J.” If you don’t have any peers, this conditional is trivial, so the Equal Weight View doesn’t rule anything out, or ratify any choice.
Another way to make the means-end conditional true is to take the modal in the consequent to be somehow or other restricted by the antecedent. (Similar moves are suggested by Thony Gillies in papers like these two.) I don’t quite know how to fill out the details of this, so I’ll leave it for another day.
So I think there are three things that Equal Weight View theorists could do to avoid the problem I started with. I don’t know which of them is best though.