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Do great minds really think alike?


Recently, a number of epistemologists (notably Feldman in Philosophers without gods: meditations on atheism and the secular life. Oxford University Press, Oxford, 2007, in Episteme 6(3):294–312, 2009; White in Philos Perspect 19:445–449, 2005, White in Contemporary debates in epistemology. Blackwell, Oxford, 2013) have argued for the rational uniqueness thesis, the principle that any set of evidence permits only one rationally acceptable attitude toward a given proposition. In contrast, this paper argues for extreme rational permissivism, the view that two agents with the same evidence (evidential peers) may sometimes arrive at contradictory beliefs rationally. This paper (1) identifies different versions of uniqueness and permissivism that vary in strength and range, (2) argues that evidential peers with different interests need not rationally endorse all the same hypotheses, (3) argues that evidential peers who weigh the theoretic virtues differently (that is, who have different standards) can sometimes rationally endorse contradictory conclusions, and finally (4) defends the permissivist appeal to standards against objections in the works of Feldman and White.

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  1. 1.

    On this picture, it would be rationally required to have, say, a credence expressed as the interval [.5, 6.1), and it would be impermissible to have a credence that is more specific than that interval.

  2. 2.

    The various kinds of doxastic attitudes and their applicability to the uniqueness and disagreement literatures are nicely summarized in Kvanvig’s (2014) Rationality and Reflection (p. 85).

  3. 3.

    Feldman considers a principle like (S-RUE) that he labels (O1):

    “For any proposition p, time t, and person S, S epistemically ought to have at t the attitude toward p that is supported by S’s evidence at t” (Feldman 2000: 678).

    Although he toys with the idea that (O1) might be correct if such attitudes are interpreted as merely dispositional, he ultimately discards (O1) in favor of a principle like (RUE), namely (O2):

    “For any person S, time t, and proposition p, if S has any doxastic attitude at all toward p at t and S’s evidence at t supports p, then S epistemically ought to have the attitude toward p supported by S’s evidence at t” (Feldman 2000: 679).

  4. 4.

    Feldman claims that “no attitude is epistemically required, but only one is epistemically permitted” (Feldman 2000: 680). In other words, Feldman thinks it is both permissible not to have any attitude toward p and permissible to have the (lone) permitted doxastic attitude toward p. This means that two different doxastic states are permitted, thus contradicting (E-RUE).

  5. 5.

    I am thankful to Andrew Moon and an anonymous reviewer for helping me to appreciate the important differences between (RUE), (E-RUE), and (S-RUE).

  6. 6.

    As with uniqueness, we could also consider an expanded version of symmetry that ranges over all doxastic states (including absences of attitudes).

  7. 7.

    Kvanvig (2014) helpfull distinguishes between synchronic and diachronic versions of uniqueness and permissivism (or “restrictivisim” and “optionalism”). All the versions of uniqueness and permissivism in this paper should be understood as synchronic theses.

  8. 8.

    This does not necessarily mean that multiple doxastic attitudes are permissible for the same person.

  9. 9.

    Rational permissivism, unlike either formulation of uniqueness, is compatible with genuine rational paradoxes, for permissivism only claims that multiple doxastic attitudes are sometimes permitted, not that they always are.

  10. 10.

    Evidential peers, like epistemic peers, have all the same evidence. They need not be equally competent. Competence is not strictly relevant to the question of whether two people can rationally come to different conclusions on the same evidence. Even fools believe rationally sometimes.

  11. 11.

    This model does not require doxastic voluntarism. We can describe beliefs (or other doxastic attitudes) as obligatory, permissible, etc., even if they are actions we cannot voluntarily perform.

  12. 12.

    Mark Nelson helped me fully see this distinction.

  13. 13.

    At least it seems so at a first glance, although perhaps certain kinds of implicit beliefs can be maintained without ever considering them.

  14. 14.

    Or, better, moderate permissivists simply believe that (RUE) and (E-RUE) are false and are not false soley because ratioanal paradoxes are possible.

  15. 15.

    See Nelson (2010), pp. 97–101 for further development of this argument. I owe thanks to Mark Nelson for patiently drawing my attention to the distinction between this argument and the argument from demandingness.

  16. 16.

    I leave aside questions about the nature of evidence and whether all evidence is ultimately propositional.

  17. 17.

    Nelson makes a similar response, though he phrases his argument in terms of act tokens and types on pp. 90–92 of the same article. Stapleford also uses the example of generosity on pp. 4073–4074 of his article.

  18. 18.

    These seem like the sort of duties in which Nelson is most interested anyway.

  19. 19.

    As with uniqueness, there are a number of candidate bestism principles that vary with respect to strength and range:

    • Expansive Epistemic Bestism For all S and for all p, S ought to have the best doxastic state toward p given her evidence.

    • Strong Epistemic Bestism For all S and for all p, S ought to have the best doxastic attitude toward p given her evidence.

  20. 20.

    Clifford famously argues that such rules are not only epistemically but also morally normative. For the purposes of this essay, we will restrict ourselves to the purely epistemic interpretation.

  21. 21.

    Someone might suggest that the best doxastic attitude toward any proposition just is to believe it if it is true and disbelieve it if it is false. Indeed, there might be an epistemic duty to believe truths and disbelieve falsehoods. This is not, however, the sort of duty anyone can have in mind when discussing rationality, for it is possible that a belief be both rational and false.

  22. 22.

    The reasoning above can be replicated with minimal adjustments to show that if (E-RUE) is true, so is expanded epistemic bestism and that if (S-RUE) is true, so is strong epistemic bestism.

  23. 23.

    Questions about maximums can be difficult even when multiple variables are not involved. Suppose Opie is \(4'6''\), and both Andy and Barney are \(6'2''\). Who is tallest? There is no good answer to this question either. Or rather, there is a good answer to this question, but it is bad English. No one person is uniquely the tallest, although Andy and Barney are both tied for being the most tall. The difficulty of this question, however, is fundamentally different than the difficulty about the best road. In the question about height, we know that Andy and Barney are tied because they have the same height. The only difficulty is that the use of a superlative in English prompts us to pick out one unique object, and in this case there is a tie between two. In the question about which road is best, we don’t even know whether or not there is a tie. Answering that the three roads are equally good would be no better than answering that one is best indisputably. Any answer we give would imply the commensurability of good-making qualities that are, in fact, incommensurable.

  24. 24.

    Just how significant the gap must be is also a matter of debate.

  25. 25.

    Though developed separately, this argument has some parallels to an argument from Douven’s (2009). Here I try to place the argument within a larger, permissivist strategy, and, in what follows, respond to uniqueness-friendly rejoinders.

  26. 26.

    At least, they are never equivalent when those assertions have contingent content.

  27. 27.

    And it is an excellent game to boot!

  28. 28.

    I owe thanks to an anonymous reviewer for pressing this point.

  29. 29.

    Most of us are often in Ahmed’s position, I imagine.

  30. 30.

    There are, of course, still propositions about Ahmed’s weighing mechanism, but they are not propositions to which Ahmed himself seems to have the right kind of access.

  31. 31.

    For an excellent discussion of these and related issues, see Feldman (2004).

  32. 32.

    That is, except in “Goliath” cases, which do not appear to be at play in the argument from abduction.

  33. 33.

    I do not mean to imply that Charlie’s beliefs are not “safe” in the technical, epistemic sense. The point is rather that certain kinds of luck (e.g. the luck of being in a position to know) are not relevant to the safety condition.

  34. 34.

    The argument from efficient evidence still shows that when interests differ, evidential peers may arrive at different—although not contrary—beliefs.

  35. 35.

    I do not mean to imply that in order to know whether one’s evidence supports a given hypothesis one must know what standards one has, only that one can (at least sometimes) know what one’s evidence supports by evaluating the evidence from a perspective that includes certain standards.


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I owe special thanks to Max Baker-Hytch, Laura Callahan, Joshua Layton-Wood, Brian Leftow, Tim Mawson, Andrew Moon, Mark Nelson, Danielle Willard-Kyle and three anonymous reviewers for their helpful comments on previous drafts of this paper. Each of them is truly a great mind.

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Correspondence to Christopher Willard-Kyle.

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Willard-Kyle, C. Do great minds really think alike?. Synthese 194, 989–1026 (2017).

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  • Rational uniqueness
  • Permissivism
  • Optionalism
  • Restrictivism
  • Disagreement
  • Epistemology
  • Evidence