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Defeasibility Theories of Knowledge

Published online by Cambridge University Press:  01 January 1976

Steven R. Levy
Steven R. Levy*
Affiliation:
University of California, Riverside
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Extract

There have been many attempts of late to formulate a satisfactory theory of knowledge with which to replace the traditional justified true belief analysis. Almost all agree that it must be the case that in order for S to know that p; i.) p be true, and ii.) S believe that p. Although many argue that there must be a condition stating that S has adequate evidence for p, requirements other than i.) and ii.) are controversial. The most popular approach taken, however, is the addition of a requirement to the effect that for S to know that p there must be no other evidence against p strong enough to undermine S's belief that p, should this evidence come to S's attention. I shall call such a requirement a “defeasibility condition” and any theory containing such a requirement a defeasibility theory.

Defeasibility theories are quite effective in handling a certain kind of difficulty to which theories of knowledge are subject, namely problems dealing with what Harman has termed the social aspect of knowledge.

Type
Research Article
Information
Canadian Journal of Philosophy , Volume 7 , Issue 1 , March 1977 , pp. 115 - 123
Copyright
Copyright © The Authors 1977

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References

* I am especially indebted to Professors John Perry, R. M. Yost, and Peter D. Klein for helpful comments on earlier versions of this paper.

1 The analysis of knowledge as justified true belief was refuted in Edmund Gettier's now famous article “Is Justified True Belief Knowlege?,” Analysis, June, 1963.

2 Among those who propose defeasibility theories are Ernest Sosa (“The Analysis of ‘Knowledge that p',” Analysis, October, 1964), Keith Lehrer and Thomas Paxson, Jr. (“Knowledge: Undefeated, Justified True Belief,” The Journal of Philosophy, April 24, 1969), Peter D. Klein (“A Proposed Definition of Propositional Knowledge,” The journal of Philosophy, August 19, 1971), Risto Hilpinen, (“Knowledge and Justification,” Ajatus, 1971), and Marshall Swain (“Epistemic Defeasibility,” American Philosophical Quarterly, January, 1974).

3 Harman, Gilbert “Knowledge, Inference and Explanation,” American Philosophical Quarterly,Vol. 3 (July, 1968).Google Scholar See VIII, The “Social Aspect” of Knowledge.

4 Lehrer and Paxson, op. cit., pp. 228–29.

5 Harman, loc. cit.

6 This is, of course, representative in that it just gives the bare bones of defeasibility theories. Examples of some early efforts can be found in Sosa, op. cit., pp. 7–8, Lehrer and Paxson, op. cit., pp. 225–31, and Kline, op. cit., p. 475.

7 I add this clause only to account for conditions added to defeasibility theories by Sosa and Lehrer and Paxson.

8 Annis, David “Knowledge and Defeasibility,” Philosophical Studies,Vol. 24 (1973), pp. 199–203.CrossRefGoogle Scholar (I have altered the notation slightly.)

9 Harman, Gilbert (“Induction,” in Induction, Acceptance and Rational Belief,ed. by Swain, Marshall 1970, D. Reidel Publishing Company, Dordrecht, Holland, pp. 83–99)Google Scholar constructs a theory of knowledge containing the principle that “There must exist no special counter-evidence to ones conclusion,” ‘special' evidence being that which undermines a claim to knowledge. In a footnote he adds, “The word ‘special’ is and is meant to be a fudge.“

10 Harman, it seems, does fall into this trap, ibid. and in Thought, 1973, Princeton University Press, Princeton,Google Scholar New Jersey, U.S.A.

11 “Epistemic Defeasibility,” American Philosophical Quarterly, January, 1974.

12 Ibid., pp. 21–22.

13 Swain, op. cit., p. 25. I have altered Swain's notation slightly. Where I have ‘p’ he has ‘h'.