Perceptual Knowledge, Discrimination, and Closure


Carter and Pritchard (Philos Stud 173(4):969–990, 2016) and Pritchard (Noûs 44(2):245–268, 2010, Epistemological disjunctivism, Oxford University Press, Oxford, 2012, Epistemic angst: radical scepticism and the groundlessness of our believing, Princeton University Press, Princeton, 2016) have tried to reconcile the intuition that perceptual knowledge requires only limited discriminatory abilities with the closure principle. To this end, they have introduced two theoretical innovations: a contrast between two ways of introducing error-possibilities and a distinction between discriminating and favoring evidence. I argue that their solution faces the “sufficiency problem”: it is unclear whether the evidence that is normally available to adult humans is sufficient to retain knowledge of the entailing proposition and come to know the entailed proposition. I submit that, on either infallibilist or fallibilist views of evidence, Carter and Pritchard have set the bar for deductive knowledge too low. At the end, I offer an alternative solution. I suggest that the knowledge-retention condition of the closure principle is not satisfied in zebra-like scenarios.

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  1. 1.

    The relevant alternatives intuition is shared by many philosophers who otherwise disagree about the relation between evidence and knowledge or the factors that determine whether an alternative is relevant. Taking a stance on these issues is certainly important to offer an account of knowledge. Fortunately, none of our arguments depends on how one fills in these details. See Cohen (1988, 1999), Dretske (1970, 1981), Lewis (1996), and Stine (1976) for different approaches. See Vogel (1999) for criticism.

  2. 2.

    See Hawthorne (2004: 34), Pritchard (2012: 68), and Williamson (2000: 117).

  3. 3.

    This assumption is relatively common in the literature. Examples include Schaffer (2005), Stine (1976), and Wright (2003). Dretske (1970: 39) has a more expansive conception of evidence but also thinks that it is not sufficient to know the denial of the cleverly disguised mule hypothesis. The present paper may be seen as an attempt to vindicate Dretske’s intuition without either rejecting the closure principle or relying on Dretske’s controversial theory of conclusive reasons.

  4. 4.

    But see Radford (1966), for a controversial counterexample to the claim that knowledge that p entails belief that p.

  5. 5.

    See Carter and Pritchard (2016: 977, 978, 980), Pritchard (2012: 68ff., 76, 80, 81, 86, 87, 95–98, 99–100, 102 n 6, 104 n 17, 105 n 19), and Pritchard (2016: 131, 132, 137). The qualification ‘normal adult human’ is meant to exclude infants and animals. There is some lack of clarity on how inclusive the class of normal adult humans is. Carter and Pritchard recognize that adult humans may sometimes be unable to know, via competent deduction, the logical consequences of their perceptual knowledge. They make room for cases involving adult humans who lack any background evidence (Pritchard 2012: 79, 83) or whose background evidence is defeated by the epistemic authority of their interlocutor (Carter and Pritchard 2016: 983). Nevertheless, their discussion is guided by the assumption that the evidence available to normal adult humans will often suffice to retain their initial knowledge and dismiss the target error-possibility. That assumption is the main target of this paper.

  6. 6.

    Ecumenism plays a key role in Pritchard’s defense of epistemological disjunctivism. He needs to defend closure without presupposing the truth of the latter (Pritchard 2012: 63, 64, 80, 82).

  7. 7.

    Pritchard formulates epistemological disjunctivism in terms of reasons, which may not be equivalent to evidence. This difference does not matter in the current context.

  8. 8.

    If seeing that p entails knowing that p, then one cannot retain one’s seeing that p without knowing that p (Williamson 2000). Pritchard (2012) rejects the entailment. I am granting Pritchard’s controversial view for the sake of the argument.

  9. 9.

    Hereafter, I abbreviate ‘recognize as…’ to ‘recognize’.

  10. 10.

    I owe this objection to a referee for this journal.

  11. 11.

    A referee for this journal urged me to discuss this argument.

  12. 12.

    See Dretske (1970: 33). For similar formulations, see Cohen (1988: 93; 1999: 62), DeRose (1995: 31 n 33), Dretske (2005: 13), Nozick (1981: 204ff.), Stine (1976: 249), and Vogel (1990: 13; 1999: 156).

  13. 13.

    Some of them come from the distinction between propositional and doxastic justification. See Sect. 3.

  14. 14.

    Of course, one could have pre-deductive knowledge of the denial of the cleverly disguised mule hypothesis. What seems wrong is to construe that knowledge as a necessary requirement to have knowledge of the zebra proposition. Otherwise, we would have trouble accommodating the idea that deduction can provide new knowledge.


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I would like to thank Arturs Logins, Davide Fassio, and two anonymous referees for their detailed and challenging comments on an earlier draft of this paper.


Funding was provided by Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (Grant No. FNS P300P1_161061/1).

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Echeverri, S. Perceptual Knowledge, Discrimination, and Closure. Erkenn (2018).

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