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The a priori defended: a defense of the generality argument


One of Laurence BonJour’s main arguments for the existence of the a priori is an argument that a priori justification is indispensable for making inferences from experience to conclusions that go beyond experience. This argument has recently come under heavy fire from Albert Casullo, who has dubbed BonJour’s argument, “The Generality Argument.” In this paper I (i) defend the Generality Argument against Casullo’s criticisms, and (ii) develop a new, more plausible, version of the Generality Argument in response to some other objections of my own. Two of these objections stem out of BonJour’s failing to fully consider the importance of the distinction between being justified in believing that an inference is good and being justified in making an inference. The final version of the argument that I develop sees the Generality Argument as one part of a cumulative case argument for the existence of a priori justification, rather than as a stand-alone knock-down argument.

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  1. 1.

    BonJour first presented the argument in Chap. 1 of his 1998, and later refines it in 2001 and 2005.

  2. 2.

    The most recent version of Casullo’s reply to the Generality Argument is in his 2003, at pp. 100–104.

  3. 3.

    Casullo (2003, p. 102).

  4. 4.

    As I shall argue later, it is quite difficult to make out the distinction between particular and general content. This difficulty will lead to a revision in my own development of the argument.

  5. 5.

    Boghossian (2001) makes the distinction and, in his response, BonJour (2001) grants that he hadn’t fully considered the importance of the distinction in his 1998. One important consequence (which BonJour concedes) of the distinction is that not all a priori insights need have propositional structure.

  6. 6.

    Casullo (2003, p. 104).

  7. 7.

    BonJour (2001, p. 673).

  8. 8.

    Now, of course, a determined skeptic will be unfazed by my above arguments, but it is of course pointless to argue with such a skeptic about anything—no arguments about any topic whatsoever will persuade such a skeptic because all arguments involve inferences. So, I direct my arguments to those who are not such determined skeptics, and, for the reason I just mentioned, its not just me that has to do this to get my argument off the ground. Everybody has to do this.

  9. 9.

    Many, but surely not all. As is by now well-known, people tend to make poor inferences in certain kinds of situations. For a good summary of this behavior, see Nisbett and Ross (1980).

  10. 10.

    The argument in this paragraph applies for both doxastic and propositional justification (Feldman and Conee (1985) call the former “well-foundedness” and the latter “epistemic justification”). Such people are plainly not doxastically justified in believing whatever principle of inference is in question because doxastic justification (or well-foundedness) requires that one actually believe whatever it is that one is doxastically justified in believing. Such people are also not propositionally justified in believing the principle of inference because to be propositionally justified in believing that a principle of inference that one employed was valid one would at least need to have some sort of reflective awareness of the kind of inference that one employed. In addition, one would also need to possess the concept of validity. But, the people mentioned fulfill neither of these requirements, and yet they seem to be justified in making an inference. So, it seems that one can be justified in making an inference without either being doxastically or propositionally justified in believing that the inference is valid or strong.

  11. 11.

    Thanks to an anonymous referee for suggesting this move.

  12. 12.

    The account of testimony presented above is consistent with anti-reductionism about testimonial justification and knowledge. For, one could hold that experience directly justifies one in believing that S says that p, and that there is a epistemic principle that says that if one is justified in believing that S says that p, then one is justified in believing that p (absent defeaters) straightaway, with no additional evidence concerning S, his reliability, or whatnot. So, when one has an experience of S saying that p, one is justified in believing that p without having an argument that justifies one in relying on S.

  13. 13.

    BonJour (1998, p. 7).

  14. 14.

    See BonJour (1998, pp. 101ff).

  15. 15.

    Antony (2004) presents a theory much like the one I described, although she doesn’t develop it much beyond how I have stated it. She spends most of the article motivating the view and discussing how it fits with Quine’s views.

  16. 16.

    Some versions of mentalism—a theory which is often classified as internalist—would be externalist enough to provide an alternative to a priori justification by understanding. For instance, if one held that all of our evidence is internal, but that we are directly justified in making certain valid and strong inferences simply because they are valid or strong, then we could be nonexperientially justified in making some inferences without being justified in making them on the basis of understanding. For what its worth, such a version of mentalism does not seem to me terribly plausible. Other versions of mentalism would not provide an escape hatch out of the Generality Argument; take, for instance, the view that all of our evidence is internal and that we are only directly experientially justified in believing propositions that are part of the content of experience.

  17. 17.

    Gilbert Harman’s epistemological conservatism can be used to make the same point. He writes, “since general conservatism is correct, everything one starts our with is defeasibly justified without appeal to anything else, so everything one starts out with is a priori in the third sense [i.e. justified without appeal to experiential evidence]” (2003, p. 28). It also provides further support to my second point, to be discussed presently.

  18. 18.

    Boghossian (2003) presents a similar argument.

  19. 19.

    The same argument works for more subtle versions of reliabilism (both process and agent) as well as for other versions of externalism. I’ll just briefly discuss two (again, simplified, but I don’t abstract away from any relevant features) other kinds of externalism. First theory: one is justified in making an inference when (i) the inference is valid or strong, and (ii) one makes the inference out of a stable disposition for making such an inference. Problem: suppose Steve had a stable disposition to make some inference J that is ridiculously complicated to prove. It doesn’t seem that Steve would be justified in making J. Second theory (inspired by Plantinga 1993): one is justified in making an inference when one makes the inference because of cognitive faculties that are functioning properly in an appropriate cognitive environment. Problem: suppose Joe was designed in such a way as to make an inference that is ridiculously complicated to prove. Again, it doesn’t seem that Joe would be justified in making such an inference, even if he were designed to make it.

  20. 20.

    It is difficult to say whether Boghossian’s theory also falls under PAP since his fullest theory appeals at bottom to a kind of pragmatic justification.

  21. 21.

    See BonJour (1998, Chap. 1) and BonJour (2005).

  22. 22.

    Remember that (1) was rendered superfluous by changing (3) to (3*). I motivated this change in §5.


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Thanks to Juan Comesaña, Alan Sidelle, Keith Yandell, and two anonymous referees for helpful comments. Thanks also to audiences at the Rochester Graduate Epistemology Conference, the 2007 Central APA Meeting, and the Young Philosophers Lecture Series at SUNY—Fredonia.

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Correspondence to Joshua C. Thurow.

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Thurow, J.C. The a priori defended: a defense of the generality argument. Philos Stud 146, 273 (2009).

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  • A priori
  • Rationalism
  • Inference