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Deficiency arguments against empiricism and the question of empirical indefeasibility


I give a brief overview of Albert Casullo’s Essays on A Priori Knowledge and Justification (2012), followed by a summary of his diagnostic framework for evaluating accounts of a priori knowledge and a priori justification. I then discuss Casullo’s strategy for countering deficiency arguments against empiricism. A deficiency argument against empiricism can be countered by mounting a parallel argument against moderate rationalism that shows moderate rationalism to be defective in a similar way. I argue that a particular deficiency argument put forth by George Bealer in “The Incoherence of Empiricism” (1992) can withstand a parallel challenge mounted by Casullo (2012, Ch.6).

I then consider Casullo’s preferred analysis of the concept of a priori justification, which identifies a belief’s being justified by some nonexperiential source as the feature by virtue of which it is justified a priori. On the analysis, an apriori-justfied belief that is justified to a degree that is sufficient for knowledge is not taken to be empirically indefeasible. I argue that Casullo could avail himself of an empirical indefeasibility requirement that is consistent with his minimal and fallibilist conception of a priori knowledge. Doing so would capture a feature of the concept of a priori knowledge that is of particular interest and significance.

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  1. 1.

    Siegel (1984) offers a similar but distinct dilemma argument against methodological naturalism.

  2. 2.

    My discussion expands on a summary of George Bealer’s argument and Al’s response to it that I present in my review of Casullo (2012) for Philosophical Quarterly (Warenski 2014).

  3. 3.

    Whether a proposition or rule that exhibits this feature is thereby warranted is a further question. See Wright (2004) for discussion.

  4. 4.

    An a priori justification might come to be empirically defeated, yet the target proposition upheld on empirical grounds. Had Euclid’s parallel postulate, understood as a claim about physical space been empirically corroborated, only the (purported) a priori status of the postulate, not the postulate itself, would have been empirically undermined.

  5. 5.

    This paragraph was added by way of clarification in response to Al’s commentary.

  6. 6.

    Field gives this argument in the context of considering the empirical indefeasibility of logic. I have substituted ‘apriori-justified proposition’ for ‘logic’ in my restatement of his puzzle.

  7. 7.

    Al suggests replacing (EI-2) with (EI-3): S’s apriori-justified belief that P cannot be defeated by any genuine empirical evidence that we can think of, given our current body of knowledge. I used ‘should’ to emphasize the evaluative component of assessments of evidential support relations, but this evaluative component could just as well be understood to be incorporated in the notion of genuine evidence.


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Warenski, L. Deficiency arguments against empiricism and the question of empirical indefeasibility. Philos Stud 173, 1675–1686 (2016).

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  • A priori knowledge
  • A priori justification
  • Albert Casullo
  • Intuition
  • Empirical indefeasibility
  • Fallibilism