Abstract
Does the fact that other people believe something give me a reason to believe it, too? Yes, and this epistemic fact is explained by the principle of common consent (PCC). PCC says that if S knows that others believe that P, then this fact gives S a reason to believe that P. Despite the fact that most logic texts file the appeal to the majority under the category of a fallacy, the principle of common consent is true. The principle can be defended by an appeal to the interpretive dilemma, a lesson from the epistemology of disagreement, an analogy to epistemic self-trust, and an inference to the best explanation for a wide range of epistemic data. Typical objections to the principle are unpersuasive and rest on either an infallibilist epistemology or an interpretive mistake.
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Notes
Perhaps a weaker version of PCC is also true. The antecedent of PCC could be weakened from ‘knows’ to some weaker epistemic state. For example, perhaps something short of knowledge, say justified belief or even mere belief, that most others believe something would be enough to generate a reason for me to believe it as well.
Thanks to an anonymous reviewer for Synthese for raising the point about how quantity and quality (and even different sorts of quality judgments) can conflict.
Kevin McCain notes that PCC could be weakened in a way that retains at least some of its explanatory potency. In particular, PCC might be weakened to say only that common consent provides a sort of presumption in favor of a belief that makes belief more reasonable than disbelief and yet falls short of saying that you actually have a reason to believe it. This is a kind of epistemic presumption described by Chisholm in Theory of Knowledge.
Thanks to an anonymous reviewer for Synthese for pointing out that conceptions of reasonable belief can be strong or weak and that the implications of PCC will vary according to which conception of reasonable belief we adopt.
http://rationalwiki.org/wiki/Argumentum_ad_populum It’s ironic that a wiki page would fail to recognize the truth of PCC. After all, wikis are built on the idea that collaborative editing is likely to generate truthful or accurate outcomes!.
Thanks to Duncan Pritchard for raising this objection.
Whether the Inverse of Disagreement argument for PCC requires adoption of the Equal Weight View of peer disagreement is unclear (though holding the Equal Weight View would be sufficient to make the argument go through). For more on the Equal Weight View, see Matheson and Carey (2013).
Does PCC have bootstrap** or easy-knowledge sorts of implications? If the fact that someone else believes that P gives me a reason to believe that P, then, does the epistemic parity argument imply that the fact that I believe that P is an additional reason to believe that P? No. Here’s why. The epistemic boost for P that is provided by the beliefs of others is parasitic on the fact that others are epistemic peers. So, it’s really the similarity to my own epistemic circumstances that provides the reason to endorse P. But I can’t then cite my OWN epistemic circumstances as an additional reason on behalf of P. Thanks to an anonymous reviewer for Synthese for raising this possibility.
Thanks to Adam Carter for raising this objection.
I note that there are some sub-sets of beliefs in which truth is probably NOT our goal. A good example of this subset is political beliefs. In that arena, it’s plausible that our goals to get to the truth are weak and often trumped by more potent goals like fitting in with those around us or signaling tribal membership. If that’s true, then PCC will have limited value in these sorts of contexts because it will be subject to a defeater. For more on this, see chapter 3 of McBrayer (2020).
Thanks to Patrick Todd for raising this objection.
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Acknowledgements
This paper originated as a talk at the University of Edinburgh in June of 2015. The audience was very helpful at sorting things out. Thanks to Adam Carter and Duncan Prichard for providing the opportunity. Thanks also to my students in Philosophical Analysis (Fall 2019) for reading the first draft of the paper and providing useful feedback. Kevin McCain and Dugald Owen each gave the final manuscript a close read and provided commentary that improved it a great deal.
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Hat tip to Dolores O’Riordan and The Cranberries. (https://en.wikipedia.org/wiki/Everybody_Else_Is_Doing_It,_So_Why_Can%27t_We%3F)
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McBrayer, J.P. Everybody else is thinking it, so why can’t we?. Synthese 198, 12071–12087 (2021). https://doi.org/10.1007/s11229-020-02850-6
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DOI: https://doi.org/10.1007/s11229-020-02850-6