Metaphysics and the Vera Causa Ideal: The Nun’s Priest’s Tale


L.A. Paul has recently defended the methodology of metaphysics on the grounds that it is continuous with the sciences. She claims that both scientists and metaphysicians use inference to the best explanation (IBE) to choose between competing theories, and that the success of science vindicates the use of IBE in metaphysics. Specifically, the success of science shows that the theoretical virtues are truth-conducive. I challenge Paul’s claims on two grounds. First, I argue that, at least in biology, scientists adhere to the vera causa ideal, which allows the theoretical virtues to play a much more limited role in scientific reasoning than Paul requires for metaphysical reasoning. The success of biology thus does not vindicate the methodology of metaphysics. Second, I argue that, at least in many cases, the successful reliance on the theoretical virtues in scientific contexts shows only that the theoretical virtues are truth-conducive within those local contexts, and not that they are truth-conducive generally. The upshots are (1) that Paul’s defense of the methodology of metaphysics fails, and (2) that any attempt to rescue her defense must pay more careful attention to what precisely is vindicated by successful science.

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  1. 1.

    For an especially clear instance of this methodology in action, see Markosian (2008). Markosian argues that, while unrestricted composition enjoys certain theoretical virtues (most notably simplicity and consistency with our background commitment to denying metaphysical vagueness), it flies in the face of our intuitive judgments about what objects exist and brings along commitments to other controversial or implausible views, and so should be rejected in favor of restricted composition.

  2. 2.

    Henceforth, I will drop this caveat and speak simply of “metaphysics,” but I will be referring only to metaphysics of the sort that Paul describes and not all of metaphysics.

  3. 3.

    See also Hawley (2006, §5) for further discussion.

  4. 4.

    E.g. Arthur (2001, p. 272): “acceptance of the occurrence of a phenomenon does not necessarily imply acceptance either of its commonness or of its power.”

  5. 5.

    The following authors treat Darwin as offering an IBE in the Origin: Thagard (1978), Lipton (2007), Doppelt (2011), Dawes (2013), Lewens (2015), Brössel (2015), Park (2015). Of these, only Lewens explicitly recognizes the Herschelian influence on Darwin’s “IBE.”

  6. 6.

    Lennox (1991) has shown the crucial role that thought experiments played for Darwin in addressing these “in principle impossible” arguments.

  7. 7.

    Lennox (2009, pp. 122–123) thinks that Hodge overstates the extent to which Darwin took the case for responsibility to concern the responsibility of natural selection (as opposed to merely supporting common descent). Though it is true that natural selection is irrelevant for explaining many of the phenomena discussed in the later chapters of the Origin, it does play a role in explaining some of them (e.g. it is essential in the discussion of embryology; Darwin 2001, pp. 439-450).

  8. 8.

    For a detailed history, see Gayon (1998). Gayon (1998, p. 398) describes the post-Origin history of Darwinism as in large part constituting an attempt “to go beyond indirect proof through explanatory power,” a description in keeping with the account of methodological standards in biology provided here.

  9. 9.

    Cf. Delpino (1869) and Mivart (2009, Chap. X) for similar criticisms.

  10. 10.

    See Novick and Scholl (manuscript) for explicit justification of adherence to the vera causa ideal as good epistemic policy.

  11. 11.

    This criticism is superficially similar to the criticism of “non-naturalistic metaphysics” offered by MacLaurin and Dyke (2012). They distinguish between scientific theories, which appeal to observation, and non-naturalistic metaphysical theories, which merely appeal to “alternative theoretical virtues.” Their argument, however, presupposes that these virtues are “more aesthetic than epistemic” and that theory choice on such grounds “is carried out completely independently of [the theories’] likely truth-value” (MacLaurin and Dyke 2012, p. 304). Because they presuppose this and do not argue for it, their argument furnishes no response to Paul’s claim that these virtues are truth-conducive. See also McLeod and Parsons (2013) for criticism of their attempt to define which metaphysical theories have observational consequences, and see Dyke and MacLaurin (2013) for a response thereto.

  12. 12.

    Benovsky (2016, Chap. 6) argues that many supposed tensions between perceptual experience and “counterintuitive” metaphysical theories (e.g. eliminativism about macroscopic objects) are not genuine tensions. I agree, but will not pursue the worry here.

  13. 13.

    Paul has offered this line of defense in personal communication.

  14. 14.

    At the end of her paper, Paul argues for the importance of the co-existence of multiple competing models in metaphysics. This is, in one sense, a form of epistemic anti-realism, for it requires that none of these models be so definitively supported as to achieve consensus. But the reason for this, on Paul’s view, is our inability to know which model actually maximizes the virtues (since different models enjoy different virtues, and it is not obvious how to weight the virtues). She is thus still committed to a methodological realism about IBE: if we knew which model maximized the virtues, we could infer to its truth.

  15. 15.

    Benovsky (2016, Chap. 7) defends something like this view. He argues that the theoretical virtues do not by themselves decide between competing theories. They must be weighted, and what decides how a philosopher weights the virtues is that philosopher’s aesthetic taste. As a result, Benovsky defends a kind of instrumentalism about metaphysics, according to which the primitive postulates of metaphysical theories are not taken to exist, but merely to serve to systematize our concepts. He writes: “What we do when we say that there is a substratum is not to say what there is in the world, rather, we introduce a new theoretical concept that allows [us] to systematize, organize, and understand the concepts of material object and property in such a way that we have a satisfactory answer to the questions we started with” (Benovsky 2016, p. 126).

  16. 16.

    Sober (2015, Chap. 2) identifies two such frameworks for understanding appeals to simplicity in scientific inference.

  17. 17.

    In fact, the reliability of parsimony analysis is controversial, and there are other ways of reconstructing phylogenies (see Wiley and Lieberman 2011, Chaps. 6–7; Sober 2015, Chap. 3). Here I will skip over this controversy, as it does not affect my point: the reasons for being skeptical of parsimony analysis are just as local as the reasons to think it justified.

  18. 18.

    There are many algorithms for actually conducting parsimony analysis, all of which make different assumptions and so are justified only insofar as those assumptions hold. For discussion, see Wiley and Lieberman (2011, Chap. 6).

  19. 19.

    Wiley and Lieberman (2011, p. 153): “The sharing of character states is always evidence that those taxa that share a character state are related unless the weight of other evidence dictates that they are of independent origin.”

  20. 20.

    Wiley and Lieberman (2011, p. 153): “The tree with the fewest number of independent origins of shared characters is the preferred solution. This is the maximum parsimony principle.”

  21. 21.

    One area of research in contemporary phylogenetic systematics involves constructing artificial datasets stipulated to result from a particular phylogeny and testing how well various algorithms succeed in recovering that phylogeny. For the phylogeny in question to produce the dataset analyzed, particular assumptions about the evolutionary process must hold. This thus allows systematists to test the manner in which different evolutionary assumptions affect the reliability of different algorithms.

  22. 22.

    Wiley and Lieberman (2011, p. 196) are explicit that weighting depends on evolutionary assumptions: “Although the investigator may think that no evolutionary assumptions are invoked when he or she decides to treat all characters as equally weighted and unordered, he or she has, in fact, made an explicit evolutionary assumption that each transformation has the same information content.”

  23. 23.

    Benovsky (2016, pp. 84–87) asks whether the simplicity of nature can justify favoring simpler metaphysical theories and concludes that it cannot, that we cannot generally assume nature to be simple. This is correct, and it is instructive to see that cladistic parsimony is justified only because it relies on an assumption with a narrower scope, about the simplicity of the evolutionary process. Benovsky ultimately claims that “the requirement for parsimony and simplicity comes from us rather than from the metaphysical reality.” It should be obvious from my arguments that this conclusion holds only if a local justification for favoring simpler theories in metaphysics, analogous to the justification of cladistic parsimony, cannot be found.


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The author thanks Zina Ward, David Colaço, Liam Kofi Bright, Eden McQueen, Adrian Currie, Jack Samuel and John Norton for comments on drafts and L.A. Paul for discussion.

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Novick, A. Metaphysics and the Vera Causa Ideal: The Nun’s Priest’s Tale. Erkenn 82, 1161–1176 (2017).

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  • Parsimony Analysis
  • Scientific Realism
  • Theoretical Virtue
  • Metaphysical Theory
  • Metaphysical Nature