Abstract
Conciliationism faces a challenge that has not been satisfactorily addressed. There are clear cases of epistemically significant merely possible disagreement, but there are also clear cases where merely possible disagreement is epistemically irrelevant. Conciliationists have not yet accounted for this asymmetry. In this paper, we propose that the asymmetry can be explained by positing a selection constraint on all cases of peer disagreement—whether actual or merely possible. If a peer’s opinion was not selected in accordance with the proposed constraint, then it lacks epistemic significance. This allows us to distinguish the epistemically significant cases of merely possible disagreement from the insignificant ones.
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Notes
The constraints typically involve a person’s having good reason to consider her disagreer(s) at least as rational, or at least as reliable with respect to the disputed sort of issue as she is herself. Disagreers (or agreers) occupying this role are sometimes termed “epistemic peers,” though Conciliationists have pointed out that at least some reduction in confidence can be required even under less stringent conditions. For a sample of what some have said on this issue, see Feldman and Warfield (2010) and Christensen and Lackey (2013).
“Conciliationism” refers to a broad family of views, according to which, a person should, upon discovering disagreement of a certain sort, revise her opinion in the direction of her disagreer. Some such views apply to credences, or partial beliefs, and typically require a person to reduce confidence in a disputed proposition. Other views apply to all-or-nothing belief, and often recommend suspension of judgment. We rely on the all-or-nothing conception in order to cast the central challenge resolved in this paper in the starkest possible terms.
Kelly (2005, p. 18).
This case was originally suggested, in outline, by Kelly (2005, p. 18).
What we refer to as the “Modal Challenge” should be distinguished from other challenges to Conciliationism involving merely possible disagreement from Kelly (2005). Specifically, Kelly discusses numerous examples involving Newcomb’s Problem that have received attention from Conciliationists. See, for example, Carey (2011), Christensen (2007), and Kornblith (2010). We will not be discussing these examples, as they raise distinct issues from the ones that arise here. The Modal Challenge deserves individual attention.
Carey and Matheson (2013) provide the only discussion we are aware of which makes any direct contact with this question. According to their view, evidence of merely possible disagreement can have epistemic significance so long as the possible disagreement is “in some important sense, ‘nearby.”’ More specifically, they hold that if there are “many nearby worlds” in which the consensus opinion diverges from the actual consensus, then this provides reason to doubt the actual consensus view. So in essence, they think that merely possible disagreement is sometimes but not always significant. Ultimately, the proposal we recommend is consonant with the Carey and Matheson view in certain broad respects. But importantly, as we will see, a satisfying solution to the Modal Challenge can be given which relies primarily on what we know from statistics, and on little else. No grappling with contentious questions about ‘nearbyness’ or the metaphysics of possible worlds more generally is necessary to solve this problem.
Note that “biased” is being used in an unusual sense.
For simplicity, let’s assume for now that the thinkers, like the coins, are statistically independent of each other. We will return to this issue later.
The foregoing passage seems to suggest that a person should view herself as merely another reliable indicator of truth among many. We opt to frame it this way solely for ease of exposition, officially staying neutral about whether a person’s own judgment screens her evidence. For discussion of this sticky issue, see White (2009), Enoch (2010), Sliwa and Horowitz (2015), Lasonen-Aarnio (2015), Weatherson (ms.).
We suspect our view can be squared with credences as well. This involves making sense of credences about probabilities. See Lewis (1980) for a discussion on this subject.
Here we follow Elga (2007), White (2009), Enoch (2010), Kelly (2010), and Christensen (2011) in defining peerhood in terms of reliability. Other discussions in the literature, including Feldman (2007), Kelly (2005), Christensen (2007), and Cohen (2013), define peerhood in terms of rationality. Ultimately, either account of peerhood would suffice for our purposes. After all, rationality is presumably relevant to peerhood because it tends to be truth-conducive. Thus, it seems that equally rational thinkers would tend to be equally reliable, and therefore, have similar probability distributions.
Suppose, for example, that the first coin has probability .75 of landing truly. Following a coin that lands truly, each coin has probability .9 of landing truly, and following a coin that lands falsely, each coin has probability .6 of landing truly. Suppose you take a sample of n flips and decide to believe the proposition that turns up most often. With n \(=\) 1, your belief has a 0.75 probability of being true. With n \(=\) 3, your belief has a 0.855 probability of being true. And with n \(=\) 5, your belief has about a 0.910 probability of being true.
In the table at the end of this section, we refer to this case as Nearby Coins.
In the table at the end of this section, we refer to this case as Nearby Thinkers.
We can think of this as a conditional probability—the probability that a given outcome is P conditional on its having been selected.
The selection constraint that we posit here is only a necessary condition on a sample’s having epistemic significance as peer disagreement. Obviously, a sample drawn from super-coins that were even more biased toward the truth would have epistemic significance as well—this is not relevant here. Additionally, at least one other constraint, that the members of a sample are statistically independent, is necessary for the sample’s having epistemic significance in proportion to its size. These two conditions—the selection constraint and statistical independence—may well be jointly sufficient for samples of peer opinion to be epistemically significant, but our main point does not depend on this assumption.
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For comments on earlier drafts and helpful discussion of relevant issues, we would like to thank David Black, David Christensen, Harry Chalmers, Nina Emery, Georgi Gardner, Joshua Schechter, and audiences at the Princeton/Rutgers Graduate Conference 2014, the APA Eastern Division 2014, the Brown University Philosophy Graduate Forum, and a seminar on the etiology of belief which met at Brown University in the fall of 2013.
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Barnett, Z., Li, H. Conciliationism and merely possible disagreement. Synthese 193, 2973–2985 (2016). https://doi.org/10.1007/s11229-015-0898-7
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DOI: https://doi.org/10.1007/s11229-015-0898-7