In This Article Expand or collapse the "in this article" section Epistemic Defeat

  • Introduction
  • General Overviews
  • Defeasible Reasoning and Justification
  • Historical Defeat/Defeasibility
  • Early Post-Gettier Defeasibility Theories of Knowledge
  • Early-21st-Century Defenses of Defeasibility Theories of Knowledge
  • Objections and Problems for Defeasibility Analyses of Knowledge
  • Externalist Approaches to the Defeat of Justification
  • Higher-Order Defeat
  • Disagreement
  • Defeasibility: Some Further Issues and Applications

Philosophy Epistemic Defeat
Patrick Bondy, Dustin Olson
  • LAST REVIEWED: 21 September 2023
  • LAST MODIFIED: 28 August 2019
  • DOI: 10.1093/obo/9780195396577-0231


Epistemic defeat has to do with the lowering, eliminating, or general downgrading of positive epistemic statuses, especially the statuses of being justified or having knowledge. On most accounts of justification, beliefs can be justified even when the property in virtue of which they are justified does not guarantee their truth. That is, justification is fallible. And for any fallibly justified belief, there is always the possibility that further information could come to light, which would render the belief unjustified once the subject becomes aware of it. When a subject becomes aware of such further information, her justification is defeated, and the defeating information (or her awareness of it) is a defeater. Furthermore, according to standard defeasibility analyses of knowledge, roughly, the existence of defeating information for a subject S’s justification for her belief that p is sufficient to prevent S from having knowledge that p, even while S is unaware of the defeating information and she retains justification for her belief. Note that knowledge is sometimes said to be defeasible, and sometimes it is said to be indefeasible. These characterizations of knowledge are compatible. When knowledge is said to be defeasible, the claim is that the justification required for knowledge is fallible, and possibly subject to defeat: roughly, the point is that it is in general possible that S knows that p on the basis of evidence E even if there are possible worlds in which S possesses E (or, there are possible worlds in which S’s belief that p is justified in the same way as in the actual world), and p is false. And it is therefore possible that the addition of some new evidence E′ to E could reduce or eliminate S’s justification for believing p on the basis of E. The addition of E′ to E would also defeat S’s knowledge that p. By contrast, when knowledge is said to be indefeasible, the claim is that if S knows that p, then there is not any actual further true proposition that would defeat S’s justification for her belief if it were conjoined to her evidence. In other words, to say that S’s knowledge that p is defeasible is to say that S can know that p in the actual world even though there are possible worlds in which there exist further facts that could come to light, which would defeat S’s justification for (and knowledge that) p. To say that S’s knowledge that p is indefeasible is to say that there are no such facts in the actual world. In general, if S knows that p in world W then S’s justification cannot be defeated by any facts that obtain in W. Although most contemporary epistemologists are fallibilists about knowledge, the claim that knowledge is indefeasibly justified true belief is compatible with both fallibilism and infallibilism about knowledge.

General Overviews

There are no textbooks or monographs devoted specifically to the topic of epistemic defeat, but the introduction to a special issue of Synthese on epistemic defeat (Moretti and Piazza 2018) provides a concise yet comprehensive survey of important work in the field. Both Grundmann 2006 and Defeaters in Epistemology provide clear, comprehensive overviews of the issues surrounding epistemic defeat. Shope 1983 contains a detailed and critical overview of early work on defeasibility analyses of knowledge.

  • Grundmann, Thomas. “Defeasibility Theory.” In The Routledge Companion to Epistemology. Edited by Sven Bernecker and Duncan Pritchard, 156–166. New York: Routledge, 2006.

    A survey article about epistemic defeaters: what is defeated, how defeaters work, different kinds of defeaters, indefeasibility, and how defeaters fit into epistemic internalism and externalism.

  • Moretti, Luca, and Tommaso Piazza. “Defeaters in Current Epistemology: Introduction to the Special Issue.” In Special Issue: Defeaters in Current Epistemology. Edited by Luca Moretti and Tommaso Piazza. Synthese 195.7 (2018): 2845–2854.

    DOI: 10.1007/s11229-017-1551-4

    Introduction to a special issue on epistemic defeaters. In addition to introducing the articles in the issue, this introduction also contains comprehensive yet concise overviews of different kinds of defeaters, epistemic statuses that defeaters can defeat, and ways defeasibility can be taken up in various other areas of epistemology.

  • Shope, Robert. The Analysis of Knowing: A Decade of Research. Princeton, NJ: Princeton University Press, 1983.

    Contains a detailed overview of various attempts to analyze knowledge in the post-Gettier literature. Chapter 2 is an extended and detailed overview of various proposals for defeasibility analyses of knowledge in the literature between 1965 and 1980, and objections to those analyses.

  • Suddath, Michael. “Defeaters in Epistemology.” Internet Encyclopedia of Philosophy.

    A general and thorough account of the central issues surrounding defeat in contemporary epistemology. Topics include defeasibility, Edmund Gettier and propositional defeaters, mental-state defeaters, and a taxonomy of defeater types.

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