Abstract
Scott Sturgeon has recently challenged Pollock’s account of undercutting defeaters. The challenge involves three primary contentions: (1) the account is both too strong and too weak, (2) undercutting defeaters exercise their power to defeat only in conjunction with higher-order beliefs about the basis of the lower-order beliefs whose justification they target, and (3) since rebutting defeaters exercise their power to defeat in isolation, rebutting and undercutting defeaters work in fundamentally different ways. My goal is to reject each of these contentions. I maintain that (1) Sturgeon fails to show that Pollock’s account of undercutting defeaters is either too strong or too weak, (2) his own account of how undercutting defeaters exercise their power to defeat is both too strong and too weak, and (3) his claim that rebutting and undercutting defeaters work in fundamentally different ways is mistaken.
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Notes
Bergmann (2006) defends the view that unsupported beliefs can be defeaters. I do not consider his arguments in this paper, but his position is open to the objection that I present against Sturgeon.
The exception is the case of a source that produces both the belief that p and the belief that not-p. Both are not justified.
Throughout this section, I assume the weak reading of ‘p is justified’ and similar expressions.
An earlier version of this paper was presented at the Workshop on Defeaters, Higher Order Evidence and the Limits of Defeat, University of Cologne, June 2015. Thanks to Thomas Grundmann for organizing the workshop and inviting me to participate, and to the workshop participants for their valuable feedback and comments.
References
Bergmann, M. (2006). Justification without awareness: A defense of epistemic externalism. Oxford: Oxford University Press.
Pollock, J. (1970). The structure of epistemic justification. American Philosophical Quarterly, 4, 62–78.
Pollock, J. (1987). Defeasible reasons. Cognitive Science, 11, 481–518.
Pollock, J. (1995). Cognitive carpentry. Cambridge, MA: MIT Press.
Pollock, J. (unpublished). Defeasible reasoning and degrees of justification. http://johnpollock.us/UnpublishedWorks/DefeasibleReasoning/DEFEASIBLEREASONING/Corrected-DefeasibleReasoningAndDegreesOfJustification/DefeasibleReasoningAndDegreesOfJustification.pdf.
Sturgeon, S. (2014). Pollock on defeasible reasons. Philosophical Studies, 169, 105–118.
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Casullo, A. Pollock and Sturgeon on defeaters. Synthese 195, 2897–2906 (2018). https://doi.org/10.1007/s11229-016-1073-5
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DOI: https://doi.org/10.1007/s11229-016-1073-5