, Volume 196, Issue 3, pp 1079–1095 | Cite as

Confirmation and the ordinal equivalence thesis

  • Olav B. VassendEmail author


According to a widespread but implicit thesis in Bayesian confirmation theory, two confirmation measures are considered equivalent if they are ordinally equivalent—call this the “ordinal equivalence thesis” (OET). I argue that adopting OET has significant costs. First, adopting OET renders one incapable of determining whether a piece of evidence substantially favors one hypothesis over another. Second, OET must be rejected if merely ordinal conclusions are to be drawn from the expected value of a confirmation measure. Furthermore, several arguments and applications of confirmation measures given in the literature already rely on a rejection of OET. I also contrast OET with stronger equivalence theses and show that they do not have the same costs as OET. On the other hand, adopting a thesis stronger than OET has costs of its own, since a rejection of OET ostensibly implies that people’s epistemic states have a very fine-grained quantitative structure. However, I suggest that the normative upshot of the paper in fact has a conditional form, and that other Bayesian norms can also fruitfully be construed as having a similar conditional form.


Bayesian confirmation Measurement theory Scales of measurement Confirmation measures Ordinal equivalence 


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© Springer Nature B.V. 2017

Authors and Affiliations

  1. 1.Department of Philosophy, School of HumanitiesNanyang Technological UniversitySingaporeSingapore

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