## 1. Disagreement and Belief




To a certain extent, it may seem that there are just three doxastic
attitudes to adopt regarding the truth of a claim: believe it's
true, believe it's false (i.e., disbelieve it), and suspend
judgment on it. In the most straightforward sense, two individuals
disagree about a proposition when they adopt different doxastic
attitudes toward the same proposition (i.e., one believes it and one
disbelieves it, or one believes it and one suspends judgment). But of
course there are levels of confidence one can have regarding a
proposition as well. We may agree that global warming is occurring but
you may be much more confident than I am. It can be useful to use
'disagreement' to cover any difference in levels of
confidence: if \(X\) has one level of confidence regarding belief
\(B\)'s truth while \(Y\) has a different level of confidence,
then they "disagree" about \(B\)--even if this is a
slightly artificial sense of 'disagree'. These levels of
confidence, or degrees of belief, are often represented as point
values on a 0-1 scale (inclusive), with larger values indicating
greater degrees of confidence that the proposition is true. Even if
somewhat artificial, such representations allow for more precision in
discussing cases.




We are contrasting disagreements about belief from disagreements about
matters of taste. Our focus is on disagreements where there is a fact
of the matter, or at least the participants are reasonable in
believing that there is such a fact.


## 2. Belief-Disagreement vs. Action-Disagreement




Suppose Jop and Dop are college students who are dating. They disagree
about two matters: whether it's harder to get top grades in
economics classes or philosophy classes, and whether they should move
in together this summer. The first disagreement is over *the truth
of a claim*: is the claim (or belief) 'It is harder to get
top grades in economics classes compared to philosophy classes'
true or not? The second disagreement is over *an action*:
should we move in together or not (the action = moving in together)?
Call the first kind of disagreement *belief-disagreement*; call
the second kind *action-disagreement*.




The latter is very different from the former. Laksha is a doctor faced
with a tough decision regarding one of her patients. She needs to
figure out whether it's best, all things considered, to just
continue with the medications she has been prescribing or stop them
and go with surgery. She confers closely with some of her
colleagues. Some of them say surgery is the way to go, others say she
should continue with medications and see what happens, but no one has
a firm opinion: all the doctors agree that it's a close call,
all things considered. Laksha realizes that as far as anyone can tell
it really is a tie.




In this situation Laksha should probably suspend judgment on each of
the two claims 'Surgery is the best overall option for this
patient' and 'Medication is the best overall option for
this patient'. When asked 'Which option is best?'
she should suspend judgment.




That's all well and good, but she still has to *do*
something. She can't just refuse to treat the patient. Even if
she continues to investigate the case for days and days, in effect she
has made the decision to not do surgery. She has made a choice even if
she dithers.




The point is this: when it comes to *belief-disagreements*,
there are three broad options with respect to a specific claim:
believe it, disbelieve it, and suspend judgment on it. (And of course
there are a great many levels of confidence to take as well.) But when
it comes to *action-disagreements*, there are just two options
with respect to an action \(X\): do \(X\), don't do
\(X\). Suspending judgment just doesn't exist when it comes to
an action. Or, to put it a different way, suspending judgment on
whether to do \(X\) does exist but is pretty much the same thing as
not doing \(X\), since in both cases you don't do \(X\) (Feldman
2006c).




Thus, there are disagreements over *what to believe* and
*what to do*. Despite this distinction, we can achieve some
simplicity and uniformity by construing disagreements over what to do
as disagreements over what to believe. We do it this way: if we
disagree over whether to do action \(X\), we are disagreeing over the
truth of the claim 'We should do \(X\)' (or 'I
should do \(X\)' or '\(X\) is the best thing for us to
do'; no, these aren't all equivalent). This translation of
action-disagreements into claim-disagreements makes it easy for us to
construe *all* disagreements as disagreements about what to
believe, where the belief may or may not concern an action. Keep in
mind, though, that this "translation" doesn't mean
that action-disagreements are just like belief-disagreements that
don't involve actions: the former still requires a choice on
what one is actually going to do.




With those points in mind, we can formulate the primary questions
about the epistemology of disagreement.




However, it is worth noting that *agreement* also has
epistemological implications. If learning that a large number and
percentage of your epistemic peers or superiors disagree with you
should probably make you lower your confidence in your belief, then
learning that those same individuals agree with you should probably
make you raise your confidence in your belief--provided they have
greater confidence in it than you did before you found out about their
agreement.




In posing the questions we start with a single individual who realizes
that one or more other people disagree/agree with her regarding one of
her beliefs. We can formulate the questions with regard to just
disagreement or to agreement and disagreement; we also have the choice
of focusing on just agreement/disagreement or going with levels of
confidence.




Here are the primary epistemological questions for just disagreement
and no levels of confidence:



> 
> **Response Question**: Suppose you realize that some people
> disagree with your belief \(B\). How must you respond to the
> realization in order for that *response* to be epistemically
> rational (or perhaps wise)?
> 
> 
> 
> **Belief Question**: Suppose you realize that some people disagree with
> your belief \(B\). How must you respond to the realization in order
> for your subsequent *position* on \(B\) to be epistemically
> rational?
> 
> 
> 




Here are the questions for agreement/disagreement plus levels of
conviction:



> 
> **Response Question\***: Suppose you realize that some people have a
> confidence level in \(B\) that is different from yours. How must you
> respond to the realization in order for that *response* to be
> epistemically rational (or perhaps wise)?
> 
> 
> 
> **Belief Question\***: Suppose you realize that some people have a
> confidence level in \(B\) that is different from yours. How must you
> respond to the realization in order for your subsequent
> *position* on \(B\) to be epistemically rational?
> 
> 
> 


## 3. Response to Disagreement vs. Subsequent Level of Confidence




A person can start out with a belief that is irrational, obtain some
new relevant evidence concerning that belief, respond to that new
evidence in a completely reasonable way, and yet end up with an
irrational belief. This fact is particularly important when it comes
to posing the central questions regarding the epistemology of
disagreement (Christensen 2011).




Suppose Bub's belief that Japan is a totalitarian state, belief
\(J\), is based on a poor reading of the evidence and a raging,
irrational bias that rules his views on this topic. He has let his
bias ruin his thinking through his evidence properly.




Then he gets some new information: some Japanese police have been
caught on film beating government protesters. After hearing this, Bub
retains his old confidence level in \(J\).




We take it that when Bub learns about the police, he has not acquired
some new information that should make him think 'Wait a minute;
maybe I'm wrong about Japan'. He shouldn't lose
confidence in his belief \(J\) merely because he learned some facts
that do not cast any doubt on his belief!




The lesson of this story is this: *Bub's action of
maintaining his confidence in his belief as a result of his new
knowledge is reasonable even though his retained belief itself is
unreasonable*. Bub's assessment of the *original*
evidence concerning \(J\) was irrational, but his reaction to the
*new* information was rational; his subsequent belief in \(J\)
was (still) irrational (because although the video gives a little
support to \(J\), it's not much). The question, 'Is Bub
being rational after he got his new knowledge?' has two
reasonable interpretations: 'Is his retained belief in \(J\)
rational after his acquisition of the new knowledge?'
vs. 'Is his response to the new knowledge rational?'




On the one hand, "rationality demands" that upon his
acquisition of new knowledge Bub drop his belief \(J\) that Japan is a
totalitarian state: after all, his overall evidence for it is very
weak. On the other hand, "rationality demands" that upon
his acquisition of new knowledge Bub keep his belief \(J\) *given
that that acquisition--which is the only thing that's
happened to him--gives him no reason to doubt* \(J\). This
situation still might strike you as odd. After all, we're saying
that Bub is being rational in keeping an irrational belief! But no:
that's not what we're saying. The statement 'Bub is
being rational' is ambiguous: is it saying that Bub's
retained belief \(J\) is rational or is it saying that Bub's
retaining of that belief was rational? The statement can take on
either meaning, and the two meanings end up with different verdicts:
the *retained belief* is irrational but the *retaining*
of the belief is rational. In the first case, a state is being
evaluated, in the second, an action is being evaluated.




Consider a more mundane case. Jack hears a bump in the night and
irrationally thinks there is an intruder in his house (he has long had
three cats and two dogs, so he should know by now that bumps are
usually caused by his pets; further, he has been a house owner long
enough to know full well that old houses like his make all sorts of
odd noises at night, pets or no). Jack has irrational belief \(B\):
there is an intruder upstairs or there is an intruder downstairs. Then
after searching upstairs he learns that there is no intruder upstairs.
Clearly, the reasonable thing for him to do is infer that there is an
intruder downstairs--that's the epistemically reasonable
*cognitive move* to make in response to the new information,
given--despite the fact that the new belief 'There is an
intruder downstairs' is irrational in an evidential sense.




These two stories show that one's action of retaining
one's belief--that intellectual action--can be
epistemically fine even though the retained belief is not. And, more
importantly, we have to distinguish two questions about the
acquisition of new information (which need not have anything at all to
do with disagreement):


* After you acquire some new information relevant to a certain
belief \(B\) of yours, what should your new level of confidence in
\(B\) be in order for *your new level of confidence regarding*
\(B\) to be rational?
* After you acquire some new information relevant to a certain belief
\(B\) of yours, what should your new level of confidence in \(B\) be
in order for *your response to the new information* to be
rational?




The latter question concerns an *intellectual action* (an
intellectual response to the acquisition of new information), whereas
the former question concerns the *subsequent level of
confidence* itself, the new confidence level you end up with,
which comes about partially as a causal result of the intellectual
action. As we have seen with the Japan and intruder stories the
epistemic reasonableness of the one is partially independent of that
of the other.


## 4. Disagreement with Superiors, Inferiors, Peers, and Unknowns




A child has belief \(B\) that Hell is a real place located in the
center of the earth. You disagree. This is a case in which you
disagree with someone who you recognize to be your *epistemic
inferior* on the question of whether \(B\) is true. You believe
that Babe Ruth was the greatest baseball player ever. Then you find
out that a sportswriter who has written several books on the history
of baseball disagrees, saying that so-and-so was the greatest ever. In
this case, you realize that you're disagreeing with
an *epistemic superior* on the matter, since you know that
you're just an amateur when it comes to baseball. In a third
case, you disagree with your sister regarding the name of the town
your family visited on vacation when you were children. You know from
long experience that your memory is about as reliable as hers on
matters like this one; this is a disagreement with a
recognized *epistemic peer*.




There are several ways to define the terms 'superior',
'inferior', and 'peer' (Elga, 2007; see section 5 below).




You can make judgments about how likely someone is compared to you
when it comes to answering 'Is belief \(B\) true?'
correctly. If you think she is more likely (e.g., you suppose that
the odds that she will answer it correctly are about 90% whereas your
odds are just around 80%), then you think she is your *likelihood
superior* on that question; if you think she is less likely, then
you think she is your *likelihood inferior* on that question;
if you think she is about equally likely, then you think she is
your *likelihood peer* on that question. Another way to
describe these distinctions is by referencing the epistemic position
of the various parties. One's epistemic position describes how
well-placed they are, epistemically speaking, with respect to a given
proposition. The better one's epistemic position, the more
likely one is to be correct.




There are many factors that help determine one's epistemic
position, or how likely one is to answer 'Is belief \(B\)
true?' correctly. Here are the main ones (Frances 2014):


* cognitive ability had while answering the question
* evidence brought to bear in answering the question
* relevant background knowledge
* time devoted to answering the question
* distractions encountered in answering the question
* relevant biases
* attentiveness when answering the question
* intellectual virtues possessed




Call these *Disagreement Factors*. Presumably, what determines
that \(X\) is more likely than \(Y\) to answer 'Is \(B\)
true?' correctly are the differences in the Disagreement Factors
for \(X\) and \(Y\).




For any given case of disagreement between just two people, the odds
are that they will not be equivalent on all Disagreement Factors:
\(X\) will surpass \(Y\) on some factors and \(Y\) will surpass \(X\)
on other factors. If you are convinced that a certain person is
clearly lacking compared to you on many Disagreement Factors when it
comes to answering the question 'Is \(B\) true?' then
you'll probably say that you are more likely than she is to
answer the question correctly provided you are not lacking compared to
her on other Disagreement Factors. If you are convinced that a certain
person definitely surpasses you on many Disagreement Factors when it
comes to answering 'Is \(B\) true?' then you'll
probably say that you are less likely than she is to answer the
question correctly provided you have no advantage over her when it
comes to answering 'Is \(B\) true?'. If you think the two
of you differ in Disagreement Factors but the differences do not add
up to one person having a net advantage (so you think any differences
cancel out), then you'll think you are peers on that
question.




Notice that in this peer case you need not think that the two of you
are equal on each Disagreement Factor. On occasion, a philosopher will
define 'epistemic peer' so that \(X\) and \(Y\) are peers
on belief \(B\) if and only if they are equal on *all*
Disagreement Factors. If \(X\) and \(Y\) are equal on all
Disagreement Factors, then they will be equally likely to judge \(B\)
correctly, but the reverse does not hold. Deficiencies of a peer in
one area may be accounted for by advantages in other areas with the
final result being that the two individuals are in an equivalently
good epistemic position despite the existence of some inequalities
regarding particular disagreement factors.




In order to understand the alternative definitions of
'superior', 'inferior', and
'peer', we will look at two cases of disagreement (Frances
2014).




Suppose I believe \(B\), that global warming is happening. Suppose I
also believe \(P\), that Taylor is my peer regarding \(B\) in this
sense: I think we are equally likely to judge \(B\) correctly. I have
this opinion of Taylor because I figure that she knows about as well
as I do the basic facts about expert consensus, she understands and
respects that consensus about as much as I do, and she based her
opinion of \(B\) on those facts. (I know she has some opinion on \(B\)
but I have yet to actually hear her voice it.) Thus, I think she is
my *likelihood peer* on \(B\).




But in another sense I don't think she is my peer on
\(B\). After all, if someone asked me 'Suppose you find out
later today that Taylor sincerely thinks \(B\) is false. What do you
think are the odds that you'll be right and she'll be
wrong about \(B\)?' I would reply with 'Over 95%!' I
would answer that way because I'm *very* confident in
\(B\)'s truth and if I find out that Taylor disagrees with that
idea, then I will be quite confident that she's wrong and
I'm right. So in that sense I think I have a *definite
epistemic advantage over her*: given how confident I am in \(B\),
I think that if it turns out we disagree over \(B\), there is a 95%
chance I'm right and she's wrong. Of course, given that I
think that we are equally likely to judge \(B\) correctly and
I'm very confident in \(B\), I'm also very confident that
she will judge \(B\) to be true; so when I'm asked to think
about the possibility that Taylor thinks \(B\) is false, I think
I'm being asked to consider a very unlikely scenario. But the
important point here is this: if I have the view that if it turns out
that she really thinks \(B\) is false then the odds that I'm
right and she's wrong are 95%, then in some sense my view is
that she's not "fully" my peer on \(B\), as I think
that when it comes to the possibility of disagreement I'm very
confident that I will be in the right and she won't be.




Now consider another case. Suppose Janice and Danny are the same age
and take all the same math and science classes through high school.
They are both moderately good at math. In fact, they almost always get
the same grades in math. On many occasions they come up with different
answers for homework problems. As far as they have been able to
determine, in those cases 40% of the time Janice has been right, 40%
of the time Danny has been right, and 20% of the time they have both
been wrong. Suppose they both know this interesting fact about their
track records! Now they are in college together. Danny believes, on
the basis of their track records, that on the next math problem they
happen to disagree about, the probability that Janice's answer
is right equals the probability that his answer is right--unless
there is some reason to think one of them has some advantage in this
particular case (e.g., Danny has had a lot more time to work on it, or
some other significant discrepancy in Disagreement Factors). Suppose
further that on the next typical math problem they work on Danny
thinks that neither of them has any advantage over the other this time
around. And then Danny finds out that Janice got an answer different
from his.




In this math case Danny first comes to think that \(B\) (his answer)
is true. But he also thinks that if he were to discover that Janice
thinks \(B\) is false, the probability that he is right and Jan is
wrong are equal to the probability that he is wrong and Janice is
right. That's very different from the global warming case in
which I thought that if I were to discover that Taylor thinks \(B\) is
false, the probability that I'm right and she's wrong are
19 times the probability that I'm wrong and she's right
(95% is 19 times 5%).




Let's say that I think you're my *conditional peer*
on \(B\) if and only if before I find out your view on \(B\) but after
I have come to believe \(B\) I think that *if* it turns out
that you disbelieve \(B\), *then* the chance that I'm
right about \(B\) is equal to the chance that you're right about
\(B\). So although I think Taylor is my likelihood peer on the global
warming belief, I don't think she is my conditional peer on that
belief. I think she is my conditional inferior on that matter. But in
the math case Danny thinks Janice is his likelihood peer *and*
his conditional peer on the relevant belief.




So, central to answering the Response Question and the Belief
Question is the following:



> 
> **Better Position Question**: Are the people who disagree
> with \(B\) in a *better epistemic position* to correctly judge
> the truth-value of the belief than the people who agree with
> \(B\)?




Put in terms of levels of confidence we get the following:



> 
> **Better Position Question\***: Are the people who have a
> confidence level in \(B\) that is different from yours in a *better
> epistemic position* to correctly judge the truth-value of the
> belief than the people who have the same confidence level as
> yours?




The Better Position Question is often not very easy to answer. For
the majority of cases of disagreement, with \(X\) realizing she disagrees
with \(Y\), \(X\) will not have much evidence to think \(Y\) is her peer, superior,
or inferior when it comes to correctly judging \(B\). For instance, if I am
discussing with a neighbor whether our property taxes will be
increasing next year, and I discover that she disagrees with me, I may
have very little idea how we measure up on the Disagreement Factors. I
may know that I have more raw intelligence than she has, but I probably
have no idea how much she knows about local politics, how much she has
thought about the issue before, etc. I will have little basis for
thinking I'm her superior, inferior, or peer. We can call these
the *unknown* cases. Thus, when you discover that you disagree
with someone over \(B\), you need not think, or have reason to think, that
she is your peer, your superior, or your inferior when it comes to
judging \(B\).




A related question is whether there is any important difference
between cases where you are justified in believing your interlocutor
is your peer and cases where you may be justified in believing that
your interlocutor is not your peer but lack any reason to think that
you, or your interlocutor, are in the better epistemic
position. Peerhood is rare, if not entirely a fictional idealization,
yet in many real-world cases of disagreement we are not justified in
making a judgment regarding which party is better positioned to answer
the question at hand. The question here is whether different answers
to the Response Question and the Belief Question are to be given in
these two cases. Plausibly, the answer is no. An analogy may help. It
is quite rare for two people to have the very same weight. So for any
two people it is quite unlikely that they are 'weight
peers'. That said, in many cases it may be entirely unclear
which party weighs more than the other party, even if they agree that
it is unreasonable to believe they weigh the exact same
amount. Rational decisions about what to do where the weight of the
party matters do not seem to differ in cases where there are
'weight peers' and cases where the parties simply lack a
good reason to believe either party weighs more. Similarly, it seems
that the answers to the Response Question and the Belief Question will
not differ in cases of peer disagreement and cases where the parties
simply lack any good reason to believe that either party is
epistemically better positioned on the matter.




Another challenge in answering the Better Position Question occurs
when you are a novice about some topic and you are trying to determine
who the experts on the topic are. This is what Goldman terms the
'novice/expert problem' (Goldman 2001). While novices
ought to turn to experts for intellectual guidance, a novice in some
domain seems ill-equipped to even determine who the experts in that
domain are. Hardwig (1985, 1991) claims that such novice reliance on
an expert must necessarily be blind, and thus exhibit an unjustified
trust. In contrast, Goldman explores five potential evidential sources
for reasonably determining someone to be an expert in a domain:


1. Arguments presented by the contending experts to support their own
views and critique their rivals' views.
2. Agreement from additional putative experts on one side or other of the
subject in question.
3. Appraisals by "meta-experts" of the experts'
expertise (including appraisals reflected in formal credentials earned
by the experts).
4. Evidence of the experts' interests and biases vis-a-vis the
question at issue.
5. Evidence of the experts' past
"track-records". (Goldman 2001, 93.)




The vast majority of the literature on the epistemic significance of
disagreement, however, concerns recognized peer disagreement (for
disagreement with superiors, see Frances 2013). We turn now to this
issue.


## 5. Peer Disagreements




Before we begin our discussion of peer disagreements it is important
to set aside a number of cases. Epistemic peers with respect to \(P\)
are in an equally good epistemic position with respect to \(P\). Peers
about \(P\) can both be in a very good epistemic position with respect
to \(P\), or they could both be in a particularly bad epistemic
position with respect to \(P\). Put differently, two fools could be
peers. However, disagreement between fool peers has not been of
particular epistemic interest in the literature. The literature on
peer disagreement has instead focused on disagreement between
competent epistemic peers, where competent peers with respect to \(P\)
are in a good epistemic position with respect to \(P\)--they are
likely to be correct about \(P\). Our discussion of peer disagreement
will be restricted to *competent* peer disagreement. In the
literature on peer disagreements, four main views have emerged: the
Equal Weight View, the Steadfast View, the Justificationist View, and
the Total Evidence View.


### 5.1 The Equal Weight View




The Equal Weight View is perhaps the most prominently discussed view
on the epistemic significance of disagreement. Competitor views of
peer disagreements are best understood as a rejection of various
aspects of the Equal Weight View, so it is a fitting place to begin
our examination. As we see it, the Equal Weight View is a combination
of three claims:



> 
> 
> *Defeat*: Learning that a peer disagrees with you about \(P\)
> gives you a reason to believe you are mistaken about \(P\).
> 
> 
> 
> *Equal Weight*: The reason to think you are mistaken about
> \(P\) coming from your peer's opinion about \(P\) is just as
> strong as the reason to think you are correct about \(P\) coming from
> your opinion about \(P\).
> 
> 
> 
> *Independence*: Reasons to discount your peer's opinion
> about \(P\) must be independent of the disagreement itself.
> 
> 
> 




Defenses of the Equal Weight View in varying degrees can be found in
Bogardus 2009, Christensen 2007, Elga 2007, Feldman 2006, and Matheson
2015a. Perhaps the best way to understand the Equal Weight View comes
from exploring the motivation that has been given for the view. We can
distinguish between three broad kinds of support that have been given
for the view: examining central cases, theoretical considerations, and
the use of analogies. The central case that has been used to motivate
the Equal Weight View is Christensen's Restaurant Check
Case.



> 
> *The Restaurant Check Case*. Suppose that five of us go out to
> dinner. It's time to pay the check, so the question we're
> interested in is how much we each owe. We can all see the bill total
> clearly, we all agree to give a 20 percent tip, and we further agree
> to split the whole cost evenly, not worrying over who asked for
> imported water, or skipped desert, or drank more of the wine. I do the
> math in my head and become highly confident that our shares are $43
> each. Meanwhile, my friend does the math in her head and becomes
> highly confident that our shares are $45 each. (Christensen 2007,
> 193.)




Understood as a case of peer disagreement, where the friends have a
track record of being equally good at such calculation, and where
neither party has a reason to believe that on this occasion either
party is especially sharp or dull, Christensen claims that upon
learning of the disagreement regarding the shares he should become
significantly less confident that the shares are $43 and significantly
more confident that they are $45. In fact, he claims that these
competitor propositions ought to be given roughly equal credence.




The Restaurant Check Case supports *Defeat* since in learning
of his peer's belief, Christensen becomes less justified in his
belief. His decrease in justification is seen by the fact that he must
lower his confidence to be in a justified position on the issue.
Learning of the disagreement gives him reason to revise and an
opportunity for epistemic improvement. Further, the Restaurant Check
Case supports *Equal Weight*, since the reason Christensen
gains to believe he is mistaken is quite strong. Since he should be
equally confident that the shares are $45 as that they are $43, his
reasons equally support these claims. Giving the peer opinions equal
weight has typically been understood to require 'splitting the
difference' between the peer opinions, at least when the two
peer opinions exhaust one's evidence about the opinions on the
matter. Splitting the difference is a kind of doxastic compromise
that calls for the peers to meet in the middle. So, if one peer
believes \(P\) and one peer disbelieves \(P\), giving the peer
opinions equal weight would call for each peer to suspend judgment
about \(P\). Applied to the richer doxastic picture that includes
degrees of belief, if one peer as a 0.7 degree of belief that \(P\)
and the other has a 0.3 degree of belief that \(P\), giving the peer
opinions equal weight will call for each peer to adopt a 0.5 degree of
belief that \(P\). It is important to note that what gets
'split' is the peer attitudes, not the content of the
relevant propositions. For instance, in the Restaurant Check Case,
splitting the difference does not require believing that the shares
are $44. Perhaps it is obvious that the shares are not an even amount.
Splitting the difference is only with respect to the disparate
doxastic attitudes concerning any one proposition (the disputed target
proposition). The content of the propositions believed by the parties
are not where the compromise occurs. Finally, the Restaurant Check
Case supports *Independence*. The reasons that Christensen
could have to discount his peer's belief about the shares could
include that he had a little too much to drink tonight, that he is
especially tired, that Christensen double checked but his friend
didn't, etc., but could not include that the shares actually are
$43, that Christensen disagrees, etc.




Theoretical support for the Equal Weight View comes from first
thinking about ordinary cases of testimony. Learning that a reliable
inquirer has come to believe a proposition gives you a reason to
believe that proposition as well. The existence of such a reason does
not seem to depend upon whether you already have a belief about that
proposition. Such testimonial evidence is some evidence to believe the
proposition regardless of whether you agree, disagree, or have never
considered the proposition. This helps motivate *Defeat*, since
a reason to believe the proposition when you disbelieve it amounts to
a reason to believe that you have made a mistake regarding that
proposition. Similar considerations apply to more fine-grained degrees
of confidence. Testimonial evidence that a reliable inquirer has
adopted a 0.8 degree of belief that \(P\) gives you a reason to adopt
a 0.8 degree of belief toward \(P\), and this seems to hold regardless
of whether you already have a level of confidence that \(P\).



*Equal Weight* is also motivated by considerations regarding
testimonial evidence. The weight of a piece of testimonial evidence is
proportional to the epistemic position of the testifier (or what the
hearer's evidence supports about the epistemic position of the
testifier). So, if you have reason to believe that Jai's
epistemic position with respect to \(P\) is inferior to Mai's,
then discovering that Jai believes \(P\) will be a weaker reason to
believe \(P\) than discovering that Mai believes \(P\). However, in
cases of peer disagreement, both parties are in an equally good
epistemic position, so it would follow that their opinions on the
matter should be given equal weight.




Finally, *Independence* has been theoretically motivated by
examining what kind of reasoning its denial would permit. In
particular, a denial of independence has been thought to permit a
problematic kind of question-begging by allowing one to use
one's own reasoning to come to the conclusion that their peer is
mistaken. Something seems wrong with the following line of reasoning,
"My peer believes not-\(P\), but I concluded \(P\), so my peer
is wrong" or "I thought \(S\) was my peer, but \(S\)
thinks not-\(P\), and I think \(P\), so \(S\) is not my peer after
all" (see Christensen (2011). Independence forbids both of these
ways of blocking the reason to believe that you are mistaken from the
discovery of the disagreement.




The Equal Weight View has also been motivated by way of analogies. Of
particular prominence are analogies to thermometers. Thermometers take
in pieces of information as inputs and given certain temperature
verdicts as outputs. Humans are a kind of cognitive machine that takes
in various kinds of information as inputs and give doxastic attitudes
as outputs. In this way, humans and thermometers are
analogous. Support for the Equal Weight View has come from examining
what it would be rational to believe in a case of peer thermometer
disagreement. Suppose that you and I know we have equally reliable
thermometers and while investigating the temperature of the room we
are in discover that our thermometers give different outputs (yours
reads '75' and mine reads '72'). What is it
rational for us to believe about the room temperature? It seems it
would be irrational for me to continue believing it was 72 simply
because that was the output of the thermometer that I was
holding. Similarly, it seems irrational for me to believe that your
thermometer is malfunctioning simply because my thermometer gave a
different output. It seems that I would need some information
independent from this 'disagreement' to discount your
thermometer. So, it appears that I have been given a reason to believe
that the room's temperature is not 72 by learning of your
thermometer, that this reason is as strong as my reason to believe it
is 72, and that this reason is only defeated by independent
considerations. If the analogy holds, then we have reason to accept
each of the three theses of the Equal Weight View.




The Equal Weight View is not the only game in town when it comes to
the epistemic significance of disagreement. In what follows we will
examine the competitor views of disagreement highlighting where and
why they depart from the Equal Weight View.


### 5.2 The Steadfast View




On the spectrum of views on the epistemic significance of
disagreement, the Equal Weight View and the Steadfast View lie on
opposite ends. While the Equal Weight View is quite conciliatory, the
Steadfast View maintains that sticking to one's guns in a case
of peer disagreement can be rational. That is, discovering a peer
disagreement does not mandate any doxastic change. While the Equal
Weight View may be seen to emphasize intellectual humility, the
Steadfast View emphasizes having the courage of your convictions.
Different motivations for Steadfast Views can be seen to reject
distinct aspects of the Equal Weight View. We have organized the
various motivations for the Steadfast View according to which aspect
of the Equal Weight View it (at least primarily) rejects.


#### 5.2.1 Denying Defeat



*Defeat* has been rejected by defenders of the Steadfast View
in a number of ways. First, *Defeat* has been denied with an
appeal to private evidence. Peter van Inwagen (1996) has defended the
Steadfast View by maintaining that in cases of peer disagreement one
can appeal to having an incommunicable insight or special evidence
that the other party lacks. The basic idea is that if I have access to
a special body of evidence that my peer lacks access to, then
realizing that my peer disagrees with me need not give me a reason to
think that I've made any mistake. After all, my peer
doesn't have everything that I have to work with regarding an
evaluation of \(P\) and it can be reasonable to think that if the peer
were to be aware of everything that I am aware of, she would also
share my opinion on the matter. Further, some evidence is undoubtedly
private. While I can tell my peer about my intuitions or my
experiences, I cannot give him my intuitions or experiences. Given our
limitations, peers can never fully share their evidence. However, if
the evidence isn't fully shared, then my peer evaluating his
evidence one way needn't show that I have mis-evaluated my
evidence. Our evidence is importantly different. While van
Inwagen's claims may entail that the two disagreeing parties are
not actually peers due to their evidential differences, these
consideration may be used to resist *Defeat* at least on looser
conceptions of peerhood that do not require evidential equality.




A related argument is made by Huemer (2011), who argues for an
agent-centered account of evidence. On this account, an experience
being *your own* evidentially counts for more than someone
else's experience. So, with this conception of evidence in hand
there will be an important evidential asymmetry even in cases where
both parties share all their evidence.




Defenders of the Equal Weight View have noted that these
considerations cut both ways (see Feldman 2006). For
instance, while you may not be able to fully share your evidence with
your peer, these same considerations motivate that your peer similarly
cannot fully share his or her evidence with you. So, the symmetry that
motivated the Equal Weight View may still obtain since both parties
have private evidence. A relevant asymmetry only obtains if one has
special reason to believe that their body of private evidence is
privileged over their peer's, and the mere fact that it is
one's own would not do this. Feldman's Dean on the Quad
case can also help make this clear.



> 
> *Dean on the Quad*. 
> Suppose you and I are standing by the window looking out on the
> quad. We think we have comparable vision and we know each other to be
> honest. I seem to see what looks to me like the dean standing out in
> the middle of the quad. (Assume that this is not something odd.
> He's out there a fair amount.) I believe that the dean is
> standing on the quad. Meanwhile, you seem to see nothing of the kind
> there. You think that no one, and thus not the dean, is standing in
> the middle of the quad. We disagree. Prior to our saying anything,
> each of us believes reasonably. Then I say something about the
> dean's being on the quad, and we find out about our
> situation. (2007, 207-208.)




Feldman takes this case to be one where both parties should
significantly conciliate even though it is clear that both possess
private evidence. While both parties can report about their
experience, neither party can give their experience to the other. The
experiential evidence possessed by each party is private. So, if
conciliation is still called for, we have reason to question the
significance of private evidence.




Second, *Defeat* has been denied by focusing on how things seem
to the subject. Plantinga (2000a) has argued that there is a sense of
justification that is simply doing the best that one can. Plantinga
notes that despite all the controlled variables an important asymmetry
remains even in cases of peer disagreement. In cases where I believe
\(P\) and I discover that my peer disbelieves \(P\), often \(P\) will
continue to seem true to me. That is, there is an important
phenomenological difference between the two peers--different
things seem true to them. Plantinga claims that given that we are
fallible epistemic creatures some amount of epistemic risk is
inevitable, and given this, we can do no better than believe in
accordance with what seems true to us. So, applied to cases of peer
disagreement, even upon learning that my peer disbelieves \(P\), so
long as \(P\) continues to seem true to me, it is rational for me to
continue to believe. Any reaction to the disagreement will contain
some epistemic risk, so I might as well go with how things seem to
me. A similar defense of Steadfast Views which emphasizes the
phenomenology of the subject can be found in Henderson et
al. 2017.




While an individual may not be to blame for continuing to believe as
things seem to them, defenders of the Equal Weight View have claimed
that the notion of epistemic justification at issue here is distinct. Sometimes doing the best one can is insufficient, and
while some epistemic risk is inevitable, it does not follow that the
options are equally risky. While your belief may still seem true to
you having discovered the disagreement, other things that seem true to
you are relevant as well. For instance, it will seem to you that your
interlocutor is an epistemic peer (that they are in an equally good
epistemic position on the matter) and that they disagree with you.
Those additional seeming states have epistemological import. In
particular, they give you reason to doubt that the truth about the
disputed belief is as it seems to you. The mere fact that your belief
continues to seem true to you is unable to save its justificatory
status. Consider the Muller-Lyer illusion:



![The Muller-Lyer Illusion is a visual illusion where two lines of the same length appear to be of different lengths. Line A has outward pointing arrows at each end of the line, whereas line B has inward pointing arrows at the end of the line. This has the effect of making line B look longer than line A.](figure1.png)



To most, line \(B\) seems to be longer, but a careful measurement
reveals that \(A\) and \(B\) are of equal lengths. Despite knowing of
the illusion, however, line \(B\) continues to seem longer to many.
Nevertheless, given that it also seems that a reliable measuring
indicates that the lines are of equal length, one is not justified in
believing that \(B\) is longer, despite it continuing to seem that
way. This result holds even when we appreciate our fallibility and
the fallibility of measuring instruments. A parallel account appears
to apply to cases of peer disagreement. Even if your original belief
continues to seem true to you, you have become aware of information
that significantly questions that seeming state. Further, we can
imagine a scenario where \(P\) seems true to me and I subsequently
discover 10,000 peers and superiors on the issue that disagree with me
about \(P\). Nevertheless, when I contemplate \(P\), it still seems
true to me. In such a case, sticking to my guns about \(P\) seems to
neither be doing the best that I can nor the reasonable thing to
do.




Third, Defeat has been denied by denying that peer opinions about
\(P\) are evidence that pertains to \(P\). Kelly (2005) distinguishes
the following three claims:


1. Proposition \(P\) is true.
2. Body of evidence \(E\) is good evidence that
\(P\) is true.
3. A competent peer believes \(P\) on the basis
of \(E\).




Kelly (2005) argues that while 3 is evidence for 2 it is not evidence
for 1. If 3 is not evidence for 1, then in learning 3 (by discovering
the peer disagreement) one does not gain any evidence relevant to the
disputed proposition. If learning of the peer disagreement
doesn't affect one's evidence relevant to the disputed
proposition, then such a discovery makes no change for which doxastic
attitude is justified for the peers to take toward the target
proposition. On this view, the discovery of peer disagreement makes no
difference for what you should believe about the disputed
proposition.




Why think that 3 is not evidence for 1? Kelly (2005) cites several
reasons. First, when people cite their justification for their
beliefs, they do not typically cite things like 3. We typically treat
the fact that someone believes a proposition as *the result of*
the evidence for that proposition, not as *another piece of*
evidence for that proposition. Second, since people form beliefs on
the basis of a body of evidence, to count their belief as yet another
piece of evidence would amount to double-counting that original body
of evidence. On this line of thought, one's belief that \(P\)
serves as something like a place-holder for the evidence upon which
one formed the belief. So, to count both the belief and the original
evidence would be to double-count the original evidence, and
double-counting is not a legitimate way of counting.




Defenders of the Equal Weight View have responded by claiming that the
impropriety in citing one's own belief as evidence for the
proposition believed can be explained in ways that do not require that
one's belief is not in fact evidence. For instance, it could be
that conversational maxims would be violated since the fact that one
believes the proposition is already understood to be the case by the
other party. Alternatively, citing one's own belief as evidence
may exhibit hubris in a way that many would want to avoid. Finally, it
seems clear that someone else's belief that \(P\) can be
evidence for \(P\), so denying that the subject's belief can be
evidence for the subject entails a kind of relativity of evidence that
some reject. Regarding the double-counting, it has been argued that
the fact that a reliable evidential evaluator has evaluated a body of
evidence to support a proposition is a new piece of evidence, one that
at least enhances the support between the body of evidence and the
target proposition. For instance, that a forensic expert evaluates the
relevant forensic evidence to support the defendant's guilt
appears to be an additional piece of evidence in favor of the
defendant's guilt, rather than a mere repetition of that initial
forensic evidence.




Finally, *Defeat* has been denied by appealing to epistemic
permissiveness. The Equal Weight View, and *Defeat* in
particular, has been thought to rely on the Uniqueness Thesis.



> 
> **Uniqueness Thesis**: For any body of evidence, \(E\),
> and proposition, \(P\), \(E\) justifies at most one competitor
> doxastic attitude toward \(P\).




If a body of evidence can only support one doxastic attitude between
belief, disbelief, and suspension of judgment with respect to \(P\),
and two people who share their evidence disagree about \(P\), then one
of them must have an unjustified attitude. So, if the Uniqueness
Thesis is true, there is a straightforward route
to *Defeat*. However, if evidence is permissive, allowing for
multiple distinct justified attitudes toward the same proposition,
then discovering that someone has evaluated your shared evidence
differently than you have need not give you any reason to think that
you have made a mistake. If evidence is permissive, then you may both
have justified responses to the shared evidence even though you
disagree. So, another way to motivate the Steadfast View is to endorse
evidential permissiveness. For reasons to reject or doubt the
Uniqueness Thesis, see Ballantyne and Coffman 2011, Conee 2009,
Frances 2014, Goldman 2010, Kelly 2010, Kopec 2015, Raleigh 2017,
Rosen 2001, and Rosa 2012.




Defenses of the Equal Weight View either defend the Uniqueness Thesis
(see Dogramici and Horowitz 2016, Greco and Hedden 2016, Matheson
2011, White 2005, White 2013) or argue that the Equal Weight View is
not actually committed to evidential uniqueness (see Christensen 2009,
Christensen 2016, Cohen 2013, Lee 2003, Levinstein 2017, Peels and
Booth 2014, and Henderson et al 2017).


#### 5.2.2 Denying Equal Weight




The Steadfast View has also been motivated by denying *Equal
Weight*. If your peer's opinion about \(P\) does not count
for as much as your own opinion, then you may not need to make any
doxastic conciliation. While most find it implausible that your own
opinion can count for more merely because it is your own, a related
and more plausible defense comes from appealing to self-trust. Enoch
(2010), Foley (2001), Pasnau (2015), Schafer (2015), Wedgwood (2007;
2010), and Zagzebski (2012) have all appealed to self-trust in
responding to peer disagreements. Foley emphasizes the essential and
ineliminable role of first-personal reasoning. Applied to cases of
disagreement, Foley claims, "I am entitled to make what I can of
the conflict using the faculties, procedures, and opinions I have
confidence in, even if these faculties, procedures, and opinions are
the very ones being challenged by others" (2001, 79). Similarly,
Wedgwood asserts that it is rational to have a kind of egocentric
bias--a fundamental trust in one's own faculties and mental
states. On this account, while peer disagreements have a kind of
symmetry from the third-person perspective, neither party occupies
that perspective. Rather, each party to the disagreement has a
first-person perspective from which it is rational to privilege
itself. Self-trust is fundamental and the trust that one must place in
one's own faculties and states simply cannot be given to
another.




Opponents have rejected the epistemic importance of the first-person
perspective (see Bogardus 2013b and Rattan 2014). While
the first-person perspective is ineliminable, it is not infallible.
Further, there are reasons from the first-person perspective to make
doxastic conciliation. It is *my* evidence the supports that my
interlocutor is my peer and *my* evidence about what she
believes which call for doxastic change. So, conciliation can be seen
to be called for from within the first-person perspective. One
needn't, and indeed cannot, abandon one's own perspective
in dealing with disagreement. There are also worries concerning what
such an emphasis on self-trust would permit. If self-trust is relevant
in cases of peer disagreement, it is difficult to see how it is not
relevant in cases of novice-expert disagreement. However, most
maintain that when the novice learns that the expert disagrees he
should make some doxastic movement if not completely defer. So,
self-trust cannot be the ultimate deciding factor in all cases of
disagreement.


#### 5.2.3 The Right Reasons View




A final motivation for the Steadfast View comes from re-evaluating the
evidential support relations in a case of peer disagreement. It will
be helpful here to distinguish between two kinds of evidence.



> 
> 
> *First-Order Evidence*: First-order evidence for \(P\) is evidence
> that directly pertains to \(P\).
> 
> 
> 
> *Higher-Order Evidence*: Higher-order evidence for \(P\) is evidence
> about one's evidence for \(P\).
> 
> 
> 




So, the cosmological argument, the teleological argument, and the
problem of evil are all items of first-order evidence regarding
God's existence, whereas the fact that a competent evaluator of
such evidence finds it to on balance support God's existence is a
piece of higher-order evidence that God exists. That a competent
evidential evaluator has evaluated a body of evidence to support a
proposition is evidence that the body of evidence in question does in
fact support that proposition.




Applied to cases of peer disagreement, the first-order evidence is
the evidence directly pertaining to the disputed proposition, and each
peer opinion about the disputed proposition is the higher-order
evidence (it is evidence that the first-order evidence supports the
respective attitudes).




The Right Reasons View is a steadfast view of peer disagreement that
emphasizes the role of the shared first-order evidence in peer
disagreements. Following Kelly (2005) we can represent the discovery of
a peer disagreement as follows:


* At \(t\), my body of evidence consists of \(E\) (the original first-order
evidence for \(P\)).
* At \(t'\), having discovered the peer disagreement, my body of
evidence consists of the following:
	1. \(E\) (the original first-order evidence for \(P\)).
	2. The fact that I am competent and believe \(P\) on the basis of 
	\(E\).
	3. The fact that my peer is competent and believes not-\(P\) on the 
	basis of \(E\).




According to the Right Reasons View, the two pieces of higher-order
evidence (ii) and (iii) are to be accorded equal weight. Having
weighed (ii) and (iii) equally, they neutralize in my total body of
evidence at t'. However, with (ii) and (iii) neutralized, I am
left with (i) and am justified in believing what (i) supports. The
Right Reasons View then notes that what I am justified in believing at
\(t\) and what I am justified in believing at t' is exactly the
same. In both cases what I should believe is entirely a matter of what
\(E\) supports, so what matters in a case of peer disagreement is what
the first-order evidence supports. If I believed in accordance with my
evidence at \(t\), then learning of the peer disagreement does nothing
to alter what I should believe about \(P\) at \(t\_2\). Having rightly
responded to my reasons at \(t\), nothing epistemically changes
regarding what attitude I should have toward \(P\).




This argument for the Right Reasons View has been responded to in
several ways. Kelly (2010) has since rejected the argument, claiming
that when a greater proportion of one's evidence supports
suspending judgment some conciliation will be called for. Since the
higher-order evidence calls for suspending judgment regarding the
disputed proposition, there will be a conciliatory push even if the
original first order evidence still plays an important role in what
attitude is justified. Others have responded to the argument by
rejecting Kelly's original description of the case (see Matheson
2009). If my evidence at \(t\) includes not only the first-order
evidence, but also the higher-order evidence about myself (ii), then
even if the new piece of higher-order evidence gained at \(t'\),
(iii), cancels out (ii) this will still call for some doxastic
conciliation from \(t\) to \(t'\). Alternatively, (ii) and (iii) can
be seen to together call for a suspension of judgment over whether
\(E\) supports \(P\). Some have argued that a justified suspension of
judgment over whether your evidence supports \(P\) has it that your
total evidence supports a suspension of judgment toward \(P\) (see
Feldman 2006 and Matheson 2015a). See Lasonen-Aarnio 2014 for an
alternative view of the impact of higher-order evidence.




A more recent defense of the Right Reasons View is found in
Titelbaum 2015. Titelbaum argues for the Fixed Point Thesis -
that mistakes about rationality are mistakes of rationality. In other
words, it is always a rational mistake to have a false belief about
rationality. So, on this view a false belief about what attitude is
rational does not 'trickle down' to affect the rationality
of the lower-level belief. Given this, if an individual's initial
response to the evidence is rational, no amount of misleading
higher-order evidence affects the rationality of that belief. A correct
response to the first-order evidence remains correct regardless of what
higher-order evidence is added.




A remaining problem for the Right Reasons View is its verdicts in
paradigm cases of peer disagreement. Many have the strong intuition
that conciliation is the Restaurant Check Case regardless of whether
you correctly evaluated the first-order evidence.


### 5.3 The Justificationist View




On the spectrum of views of the epistemic significance of
disagreement, the Justificationist View lies somewhere in between the
Equal Weight View and the Steadfast View. In defending the
Justificationist View, Jennifer Lackey agrees with the Equal Weight
View's verdicts in cases like the Restaurant Check Case, but
thinks that not all cases should be handled in this way. Along these
lines she gives the following:



> 
> *Elementary Math*. Harry and I, who have been colleagues for
> the past six years, were drinking coffee at Starbucks and trying to
> determine how many people from our department will be attending the
> upcoming APA. I, reasoning aloud, say, 'Well, Mark and Mary are
> going on Wednesday, and Sam and Stacey are going on Thursday, and
> since 2+2=4, there will be four other members of our department at
> that conference.' In response, Harry asserts, 'But 2+2
> does not equal 4.' (Lackey 2010a, 283.)




In Elementary Math, Lackey finds it implausible that she should
become less confident that 2+2=4, never mind to split the difference
with her interlocutor and suspend judgment about the matter. In other
words, the claim is that the Equal Weight Views gives the wrong
verdicts in what we might call cases of 'extreme
disagreement'. What justifies treating Elementary Math
differently than the Restaurant Check Case? According to Lackey, if
prior to discovering the peer disagreement you are highly justified in
believing the soon to be disputed proposition, then upon discovering
the peer disagreement little to no conciliation is called for. So,
since Lackey is highly justified in believing that 2+2=4 prior to
talking to her colleague, not conciliation is called for, but since
Christensen was not highly justified in believing that the shares are
$43 prior to discovering the disagreement, a great deal of conciliation
is called for. According to the Justificationist View, one's
antecedent degree of justification determines the rational response to
peer disagreement. Strong antecedent justification for believing the
target proposition matters since when coupled with the discovered
disagreement you now have reasons to believe your interlocutor is not
your peer after all. In Elementary Math, Lackey should significantly
revise her views about her colleague's epistemic position
regarding elementary math. In contrast, the Restaurant Check Case calls
for no similar demotion. This difference is explained by the differing
degrees of antecedent justification.




Applied to our framework, the Justificationist View denies
*Independence*. In cases where you first-order evidence strongly
supports believing p, this fact can be used to reassess your
interlocutor's epistemic credentials. *Independence* only
permitted information from 'outside' the disagreement to
affect assessment of peerhood credentials, but here, the fact that your
interlocutor disagrees with something you are highly justified in
believing give you a reason to discount his opinion on the matter.




Lackey defends the legitimacy of such a demotion due to the
existence of personal information. In any case of peer disagreement, I
will have information about myself that I simply lack (or lack to the
same extent) regarding my interlocutor. I will always be more aware of
my alertness, sincerity, open-mindedness, and so forth, than I will be
of my interlocutor. A similar claim is defended in Benjamin 2015. This
asymmetry, when coupled with my high antecedent justification for
believing the disputed proposition makes it rational to demote my
alleged peer. Since in extreme disagreements one party is severely
malfunctioning, my personal information makes the best explanation of
this fact that it is my peer who is malfunctioning.




The Justificationist View has been criticized in several ways. Some
object that high antecedent justification for believing the target
proposition can make the relevant difference (see Christensen 2007,
Vavova 2014a, 2014b). Consider the following case:



> 
> *Lucky Lotto*. You have a ticket in a million-ticket
> lottery. Each ticket is printed with three six-digit numbers that,
> when added, yield the seven-digit number that is entered into the
> lottery. Given the odds, I am highly justified in believing that your
> ticket is a loser, but I nevertheless add the numbers on your ticket
> just for fun. Having added the numbers and comparing the sum to the
> winning number - no match - I thereby become even more
> justified in believing that you did not win. Meanwhile, you are adding
> up your numbers as well, and comparing them to the winning number. You
> then exclaim 'I won!' (Christensen 2007,
> 200.)




In this case, I have very high antecedent justification for
believing that your ticket is not a winner. Nevertheless, upon hearing
you exclaim that you won, the rational response is not to downgrade
your epistemic credentials. Even high antecedent justification can be
defeated by new information.




Others have agreed that personal information can act as symmetry
breaker giving the subject some reason to privilege their own view but
deny that such an advantage would be had in suitably idealized cases of
peer disagreement (Matheson 2015a). The use of personal information to
discount your interlocutor's opinion would not violate
*Independence*, so the defender of the Equal Weight View
needn't disagree on this score.


### 5.4 The Total Evidence View




Like the Justificationist View, the Total Evidence View lies somewhere
between the Steadfast View and the Equal Weight View. The Total
Evidence View claims that in cases of peer disagreement, one is
justified in believing what one's total evidence supports (Kelly
2010). While this might sound like something of a truism, central to
the view is an additional claim about the relation between first-order
evidence and higher-order evidence. Let's first revisit the
Equal Weight View. According to the Equal Weight View, in a peer
disagreement where one individual has a 0.7 degree of belief that
\(P\) and the other has a 0.3 degree of belief that \(P\), both peers
should split the difference and adopt a 0.5 degree of belief that
\(P\). On the Equal Weight View, then, the attitude that you are
justified in adopting toward the disputed proposition is entirely
determined by the higher-order evidence. The justified attitude is the
mean between the two peer attitudes, which ignores what their shared
first-order evidence supports. According to the Total Evidence View,
this is a mistake - the first-order evidence must also factor in
to what the peers are reasonable in believing. Such an incorporation
of the first-order evidence is what leads to the name "Total
Evidence View".




Kelly gives the following case to motivate the view:



> 
> *Bootstrapping*. At time \(t\_0\), each of us has access to a
> substantial, fairly complicated body of evidence. On the whole this
> evidence tells against hypothesis \(H\): given our evidence, the
> uniquely rational credence for us to have in \(H\) is 0.3. However, as
> it happens, both of us badly mistake the import of this evidence: you
> adopt a 0.7 degree of belief toward \(H\) while I adopt a 0.9 degree
> of belief. At time \(t\_1\), we meet and compare notes and we then
> split the difference and converge on a 0.8 degree of belief. (Kelly
> 2010, 125-126.)




While the Equal Weight View seems to be committed to the peers being
justified in adopting the 0.8 degree of belief in \(H\), Kelly finds such a
consequence implausible. After all, both peers badly misjudged the
first-order evidence! This argument can be seen as an argument against
*Independence*. In these cases, the disputed first-order
evidence can exert an 'upwards epistemic push" to mitigate
the impact of the higher-order evidence. Kelly takes Independence on
directly with the following case:



> 
> *Holocaust Denier*. I possess a great deal of evidence that the
> Holocaust occurred, and I judge it to strongly support that
> hypothesis. Having adopted a high amount of credence that the
> Holocaust occurred, I encounter an individual who denies that the
> Holocaust ever occurred (because he is grossly ignorant of the
> evidence). (Kelly 2013b, 40)



*Independence* claims that my reasons for believing \(P\) cannot
be used to discount my interlocutor's opinion about \(P\). Absent
those first-order reasons, however, Kelly doubts that there is much
left to work with the discount the interlocutor, and the drastic
conciliation that should result without a good reason to discount his
opinion is implausible.




This motivation for the Total Evidence View has been responded to in
several different ways. One route of response is deny Kelly's
assessment of the cases (Matheson 2015a). According to this response,
the individuals in Bootstrapping were both presented with powerful,
though misleading, higher-order evidence. However, misleading evidence
is evidence nevertheless. Given this, it can be argued that the
individuals still correctly responded to their total body of evidence.
For instance, we can imagine a logician working on a new proof. Suppose
that it seems to him that he has successfully completed the proof, yet
he nevertheless has made a subtle error rendering the whole thing
invalid. In such a case, the logician has significantly mis-evaluated
his first-order evidence, yet he has strong higher-order evidence that
he is good at things like this. Suppose he then shows his work to a
capable colleague who also maintains that the proof is successful. In
this case, it may seem that it is rational for the logician to believe
that the proof is successful, and perhaps be quite confident, even
though this conclusion is significantly different from what the
first-order evidence supports. According to this rejoinder, the call to
split the difference is best seen as addressing the Belief
Question.




A second route of response is to emphasize the distinction between
the Response Question and the Belief Question. According to this
response, while there may be something epistemically defective about
the final doxastic states of the individuals in Bootstrapping, they
nevertheless had the rational response to the higher-order evidence
(Christensen 2011). The fact that they each misjudged the original
evidence is an epistemic flaw that carries over to their final doxastic
attitude, but on this line of thinking the doxastic response that each
party made upon comparing notes was nevertheless rational. According to
this rejoinder, the call to split the difference is best seen as
addressing the Response Question.


### 5.5 Other Issues




Other objections to the Equal Weight View are not tied to any other
particular view of disagreement, and some apply to more than just the
Equal Weight View. In this section we briefly examine some of these
objections.


#### 5.5.1 Self-Defeat




A prominent objection to the Equal Weight View and other views that
prescribe doxastic conciliation is that such views are self-defeating.
For expressions of this objection, see Elga 2010, Frances 2010,
O'Connor 1999, Plantinga 2000a and 2000b, Taliaferro 2009,
Weatherson 2014, and Weintraub 2013. For responses, see Bogardus 2009,
Christensen 2009, Elga 2010, Graves 2013, Kornblith 2013, Littlejohn
2013, Matheson 2015b, and Pittard 2015. In brief, there is disagreement
about the epistemic significance of disagreement itself, so any view
that calls for conciliation upon the discovery of disagreement can have
it that it calls for its own rejection. For instance, a defender of the
Equal Weight View could become aware of enough individuals that are
suitably epistemically well-positioned on the epistemology of
disagreement that nevertheless deny that the Equal Weight View is
correct. Following the prescriptions of the Equal Weight View would
require this defender to abandon the view, and perhaps even accept a
competitor account. For these reasons, Plantinga (2000a) has claimed
that such views are, 'self-referentially inconsistent'
(522) and Elga (2010) has claimed that such views are
'incoherent' and 'self-undermining' (179). Such
a worry seems to apply to the Equal Weight View, the Justificationist
View, and the Total Evidence View. Since all three views prescribe
conciliation in at least some cases, they are all (at least in
principle) subject to such a result.




Defenders of these conciliatory views have responded in a number of
ways. First, some emphasize the way in which these views are
self-defeating is not a way that shows these views to be false, or
incapable of being true. 'No true sentences have
more than 5 words' may also be said to be self-defeating, but
this is a different kind of defeat. At its worst, the consequences here
for conciliatory views is that given certain contingent circumstances
they cannot be reasonably believed, but such an inability to be
reasonably believed does not demonstrate their falsity. Further, a
skeptical attitude toward the epistemic significance of disagreement
seems to fit the spirit of these views quite well (more on this
below).




Another way such a consequence has been downplayed is by comparing
it to other principles that share the same result. Along these lines,
Christensen gives the following:



> 
> *Minimal Humility*. If I have thought casually about \(P\) for
> 10 minutes, and have decided it is correct, and then find out that
> 1000 people, most of them much smarter and more familiar with the
> relevant evidence and arguments than I, have thought long and hard
> about \(P\), and have independently but unanimously decided that \(P\)
> is false, I am not justified in believing \(P\). In fact, I am
> justified in disbelieving \(P\). (2009, 763.)




The principle of Minimal Humility is quite plausible, yet there are
contingent circumstances under which it calls for its own rejection
too. If such a consequence is untenable, then it would call for the
rejection of principles beyond those endorsed by the Equal Weight View,
the Justificationist View, and the Total Evidence View.




A final response argues that these principles about disagreement are
themselves exempt from their conciliatory prescriptions. So, correctly
understood, these principles call for conciliation in ordinary
disagreements, but prescribe remaining steadfast in disagreements about
disagreements. So on this view, the true principles are not
self-defeating. Several philosophers have endorsed such a response to
the self-defeat worry. Bogardus (2009) argues that we can 'just
see' that conciliatory principles are true and this prevents them
from being self-undermining. Elga (2010) argues that conciliatory
views, properly understood, are self-exempting since fundamental
principles must be dogmatic about their own correctness. Pittard (2015)
argues that remaining resolute in conciliationism is no more
non-deferential than being conciliatory about conciliationism. The
reasoning here is that to conciliate about one's conciliatory
principles would be deferential about one's belief or credence,
but steadfast about one's reasoning. So, once we appreciate the
distinct levels of belief/credence and reasoning, either response to a
disagreement about the significance of disagreement will require being
steadfast at one level. This, argues Pittard, makes remaining steadfast
about conciliationism unproblematic.




While such responses would avoid the self-defeat charge, some see it
guilty of arbitrariness (see Pittard 2015, Blessenohl 2015).


#### 5.5.2 Formal issues




A further set of issues regarding the Equal Weight View come from
considerations within formal epistemology. Fitelson and Jelhe (2009)
argue that there are difficulties in making precise the Equal Weight
View along Bayesian lines. In particular, they argue that the most
intuitive understandings of the Equal Weight View have untenable
consequences. Gardiner (2014) and Wilson (2010) each raise an
objection that Equal Weight View (at least as typically understood)
violates the principle of commutativity of evidence. If we imagine an
individual encountering a number of disagreeing peers sequentially,
then which doxastic attitude is reasonable for the peer will depend
upon the order at which the peers are confronted. However, the
principle of commutativity of evidence claims that the order of
evidential acquisition should not make such a
difference. Lasonen-Arnio (2013) sets up a trilemma for the Equal
Weight View arguing that either (i) it violates intuitively correct
updates, (ii) it places implausible restrictions on priors, or (iii)
it is non-substantive.


#### 5.5.3 Actual Disagreement and Possible disagreement




Another issue concerns which disagreements are of epistemic
significance. While actual peer disagreement is rare, if not
non-existent (see below), merely possible peer disagreement is
everywhere. For any belief you have, it is possible that an epistemic
peer of yours disagrees. Since we are fallible epistemic agents,
possible peer disagreement is inevitable. One challenge is to
distinguish the epistemic significance of actual peer disagreement
from the significance of merely possible peer disagreement. Kelly
(2005) first raises this challenge. After all, whether this possible
disagreeing peer actually exists is a contingent and fragile matter,
so to only care about it may be to exhibit an 'actual world
chauvinism'. (This term comes from Carey 2011.)




Christensen (2007) responds to this challenge by noting that while
merely possible disagreement only shows that we are fallible, actual
disagreement demonstrates that someone has in fact made a mistake.
Since we are already aware that we are fallible epistemic agents,
thinking about possible peer disagreements does not add any information
that calls for (further) doxastic change. In contrast, discovering an
actual peer disagreement gives us information that we lacked. In a case
of peer disagreement, one of the parties has made a mistake. While the
possibility of error does not demand belief revision, an increase in
the probability of having made an error does.




A further question is whether actual peer disagreements are the only
peer disagreements with epistemic significance. For instance, suppose
that you have created an argument that you find sound in the solitude
of your office. When thinking about what your (peer) colleague would
think, suppose that you reasonably conclude that she would disagree
about the merits of your argument. If such a conclusion is reasonable
for you, then it seems that this fact should have some epistemic
consequences for you despite the fact that there is not (at least as of
yet) any actual disagreement. Arguably, such a merely possible
disagreement even has the same epistemic significance as an actual
disagreement (see Carey & Matheson 2013). Similarly, if an evil
tyrant believes \(P\) and then chooses to eliminate all disagreeing peers
who believe not-\(P\), he would not thereby become justified in his
previously contentious belief (Kelly 2005). A challenge is to pick out
which merely possible disagreements are epistemically significant,
since at the risk of global skepticism, clearly not all are (Barnett
and Li 2017). Issues surrounding counterfactual disagreement are also
examined in Ballantyne 2013b, Bogardus 2016, and Morgensen 2016.


#### 5.5.4 Irrelevance of Peer Disagreement




A final issue concerns peer disagreement itself. As some have noted,
epistemic peers are extremely rare, if not non-existent (Frances 2010,
2014; King 2011; Matheson 2014). After all, what are the odds
that someone else is in precisely as good of an epistemic position as
you on some matter--and even she was, would you know it? As we
have seen, there are a number of disagreement factors, and the odds
that they end in a tie between any two individuals at any given time is
quite unlikely. The paucity of peers may be taken to show that the
debate of the epistemic significance of peer disagreement is a futile
exercise in extreme hypotheticals. After all, if you have no epistemic
peers that disagree with you, doesn't the epistemic threat from
disagreement dissolve? Further, there may seem to have been a deceptive
shift in the debate. Much of the puzzle of disagreement is motivated by
messy real world cases of disagreement, but the vast majority of the
literature is focused on idealized cases of disagreement that rarely,
if ever, occur.




There are several reasons to think about the significance of peer
disagreement beyond its intrinsic appeal. First, considering the
idealized cases of peer disagreement helps to isolate the epistemic
significance of the disagreement itself. By controlling for other
epistemic factors, cases of peer disagreement help us focus on what
epistemic effects discovered disagreement has. While in non-idealized
cases this is but one factor in determining what to believe, the debate
about peer disagreements attempts to help us better understand this one
factor. Second, while peers may be quite rare, as we have noted above,
it is often not clear which party is in the better epistemic position.
For instance, while it is quite rare for two individuals to be the
exact same weight, it can often be unclear which individual weighs
more. These unknown cases may have the same epistemic significance as
peer cases. If what is needed is a positive reason to privilege
one's own view, as opposed to positive reasons to think that the
other is a peer, then unknown cases should be treated like peer
cases.




In what follows we turn to examining the epistemic significance of
disagreement outside of these idealized cases of peer disagreement.


## 6. Disagreement By the Numbers




Many disagreements are one-on-one: one person disagrees with another
person and as far as they know they are the only two who have any
opinion on the matter. Lisa thinks that she and Marie should move in
together; then Lisa discovers that Marie has the opposite opinion. Bob
and his sister Teri disagree about whether their father had an affair
when they were children. In this case they know that others have the
answer--their father, for one--but for various reasons the
opinions of others are not accessible.




Many other disagreements involve just a few people. Bob, Rob, Hob, and
Gob work in a small hotel and are wondering whether to ask for raises
in their hourly pay rate. After discussion Bob thinks they should, Rob
and Hob think they shouldn't, and Gob is undecided. When Bob
learns all this about his three colleagues, what should his doxastic
reaction be to this mixed bag of agreement and disagreement?




However, when it comes to many of your beliefs, including some of the
most interesting ones, you are fully aware that *millions* of
people disagree with you and *millions* of other people agree
with you. Just consider a belief about religion--just about any
belief at all, pro or con. You must have *some* views on
controversial matters; virtually every human does. Moreover,
you're perfectly aware that they are controversial. For the most
part, it's not as though you believe \(B\), \(B\) happens to be
controversial, but you had no idea it was controversial.




Moreover, when it comes to these controversial beliefs that large
numbers of people have taken positions on, it's often the case
that there are experts on the matter. In many cases the experts have a
definite opinion: global warming is happening and the earth is many
millions of years old. Other times they don't: electrons and
quarks come from "strings".




If the numbers matter, then disagreement poses a skeptical threat for
nearly every view of the significance of peer disagreement. The
skeptical threat for conciliatory views (the Equal Weight View, the
Justificationist View, and the Total Evidence View) is pretty
straightforward. On the Equal Weight View, since for many
controversial beliefs we are not justified in believing that the
weighing of opinions favors our own opinion on the matter, the reasons
for thinking that we are mistaken outweigh our reasons for thinking we
are correct. The added resources of the Justificationist View and the
Total Evidence View also do not seem to help in resisting the
skeptical conclusion. For many controversial views we lack the strong
first-order evidence and high antecedent justification that these
views utilize to mitigate the call to conciliate. Further, while
appeals to personal information may be good symmetry-breakers in cases
of one-to-one disagreement, when the numbers of disagreeing parties
are much larger, the effectiveness of such appeals radically
diminishes. Similar considerations apply to most Steadfast Views. Most
defenses of Steadfast Views attempt to find a symmetry-breaker in the
peer-to-peer disagreement that allow for one to privilege one's
own belief. For instance, even if self-trust or private evidence can
give one a reason to privilege their own belief, such a
symmetry-breaker is seemingly not up to the task when the belief in
question is a minority view. Given that most controversial beliefs in
science, religion, politics, and philosophy are minority views, it
appears that even if many Steadfast Views of peer disagreement are
correct, they still face a skeptical challenge regarding disagreement
more generally. The notable exception here is the Right Reasons
View. Since according to the Right Reasons View, what one is justified
in believing is entirely determined by the first-order evidence, no
amount of discovered disagreement would change which controversial
beliefs are rational. While the Right Reasons View, may be safe from
such skeptical concerns, such safety only comes by way of what many
see as the feature that makes it implausible. For instance, the Right
Reasons View has it that you can be justified in believing \(p\) even
when you are aware that every other peer and superior to you believes
not-\(p\). While this avoids the more general skeptical threat, many
see this as too high a price.




Another issue concerning how the numbers matter regards the
independence of the relevant opinions. Our beliefs are shaped by a
number of factors, and not all of them are epistemically
relevant. Certain religious beliefs, political beliefs, and even
philosophical beliefs are correlated with growing up in particular
regions or going to certain schools. For this reason, it may be
thought that the agreement of individuals who came to their opinions
on a matter independently count for more, epistemically speaking, then
agreement of individuals with a greater shared background. For more on
this issue, see Carey & Matheson 2013, Goldman 2001, and Lackey 2013b.


## 7. Disagreement and Skepticism




So, the phenomenon of disagreement supplies a *skeptical
threat*: for many of our cherished beliefs. If we aren't
sheltered, then we know that there is a great deal of controversy
about those beliefs even among the people who are the smartest and
have worked the hardest in trying to figure out the truth of the
matter. There is good reason to think that retaining a belief in the
face of that kind of controversy is irrational, and a belief that is
irrational does not amount to knowledge. It follows that our beliefs
we recognize as controversial do not amount to knowledge. This is the
threat of *disagreement skepticism* (Frances 2018, 2013, 2005;
Christensen 2009; Fumerton 2010; Goldberg 2009, 2013b; Kornblith 2010,
2013; Lammenranta 2011, 2013; Machuca 2013).




For the sake of argument, we can assume that our controversial
beliefs *start out* epistemically rational. Roughly put, the
disagreement skeptic thinks that even if a controversial belief starts
out as rational, once one appreciates the surrounding controversy,
one's belief will no longer be rational, and thus not an item of
knowledge. The disagreement skeptic focuses on beliefs that satisfy
the following recognition-of-controversy conditions.




You know that the belief \(B\) in question has been investigated and
debated (i) for a very long time by (ii) a great many (iii) very smart
people who (iv) are your epistemic peers and superiors on the matter
and (v) have worked very hard (vi) under optimal circumstances to
figure out if \(B\) is true. But you also know that (vii) these
experts have not come to any significant agreement on \(B\) and (viii)
those who agree with you are not, as a group, in an appreciably better
position to judge \(B\) than those who disagree with you.




Notice that the problem does not emerge from a mere lack of
consensus. Very few, if any, beliefs are disagreement-free. Rather,
the skeptical threat comes from both the extent of the disagreement
(conditions (i) and (ii)) and the nature of the disagreeing parties
(conditions (iii) - (viii)). While not every belief meets these
recognition-of-controversy conditions, many do, and among those that
do are some of our most cherished beliefs.




For instance, I might have some opinion regarding the nature of free
will or the moral permissibility of capital punishment or whether God
exists. I know full well that these matters have been debated by an
enormous number of really smart people for a very long time--in
some cases, for centuries. I also know that I'm no expert on any
of these topics. I also know that there are genuine experts on those
topics--at least, they have thought about those topics
*much* longer than I have, with a great deal more awareness of
relevant considerations, etc. It's no contest: I know I'm
just an amateur compared to them. Part of being reflective is coming to
know about your comparative epistemic status on controversial subjects.
That said, being an expert in the relevant field doesn't remove
the problem either. Even if I am an expert on free will, I am aware
that there are many other such experts, that I am but one such voice
among many, and that disagreement is rampant amongst us.




The person who knows (i)-(viii) is robbed of the reasonableness
of several comforting responses to the discovery of controversy. If
she is reasonable, then she realizes that she can't make, at
least with confidence, anything like the following remarks:


* Well, the people who agree with me are smarter than the people who
disagree with me.
* We have crucial evidence they don't have.
* We have studied the key issue a great deal more than they
have.
* They are a lot more biased than we are.




This phenomenon is particularly prevalent with regard to religion,
politics, morality, and philosophy. If when it comes to debates about
free will, capital punishment, affirmative action, and many other
standard controversial topics you say to yourself regarding the
experts who disagree with you 'Those people just don't
understand the issues', 'They aren't very
smart', 'They haven't thought about it much',
et cetera, then you are doing so irrationally in the sense
that *you should know better* than to say that, at least if
you're honest with yourself and informed of the state of the
debate over free will.




However, connection between controversy and skepticism won't
apply to many of our other beliefs. No one (or no one you know) is
going around saying your parents don't love you, you
aren't a basically moral person, etc. So those beliefs are
probably immune to any skeptical argument of the form 'There is
long-standing disagreement among experts regarding your belief \(B\);
you know all about it (viz. conditions (i)-(viii)); you have no
good reason to discount the ones who disagree with you; so, you
shouldn't retain your belief \(B\)'. This is not to say
that those beliefs escape all skeptical arguments based on human error
and related phenomena. But, the first thing to note about disagreement
skepticism is that it is *contained*. Only beliefs that meet
something like the recognition-of-controversy conditions are subject
to this skeptical threat. Interestingly, however, it is not itself
exempt from these skeptical consequences. Such views of disagreement
are themselves quite controversial, so here too is another place where
the self-defeat worry arises.




Disagreement skepticism is also *contingent*. The nature and
extent of disagreements are both contingent matters, so since
disagreement skepticism relies on these factors, the skeptical
consequences of disagreement are also contingent. At one point in time
the shape of the Earth was quite contentious. While there is not now
universal agreement that the Earth is roughly spherical, the
recognition-of-controversy conditions are no longer met on this matter.
Similarly, issues of great current controversy may too at some point
fail to meet the recognition-of-controversy conditions. So, the
skeptical threat from disagreement can come and go. That said, the
track-record for the staying power of various philosophical
disagreements strongly indicates that they aren't going anywhere
anytime soon.




Finally, disagreement skepticism is exclusively epistemic. At issue
here has solely been one's epistemic reasons for holding a
belief. Meeting the recognition-of-controversy conditions raises a
problem for these reasons, but we haven't said anything about
what moral, prudential, or even religious reasons you may have for
holding a controversial belief. The skeptical threat from disagreement
only concerns our epistemic reasons. Relatedly, if there is an
all-things-considered norm of belief, disagreement skepticism may have
some implications for this norm, but only by way of addressing the
epistemic reasons that one has for belief.




A related point is that these consequences are doxastic
consequences. Disagreement skepticism is about what beliefs are/are
not rational and which changes in confidence are/are not rational.
Disagreement skepticism is not a view about which views should be
defended or what theses should be further researched. When coupled
with the knowledge norm of assertion or the knowledge norm of action,
disagreement skepticism would have further consequences about what
claims can be asserted or acted upon, but these consequences only
follow from such a combination of views.