Acta Analytica

, Volume 29, Issue 4, pp 491–505 | Cite as

On Not Counting the Cost: Ad Hocness and Disconfirmation

  • Lydia McGrew


I offer an account of ad hocness that explains why the adoption of an ad hoc auxiliary is accompanied by the disconfirmation of a hypothesis H. H must be conjoined with an auxiliary (or set of auxiliaries) a′, which is improbable antecedently given H, while ~H does not have this disability. This account renders it unnecessary to require, for identifying (bad) ad hocness, that either a′ or H have a posterior probability less than or equal to 0.5; there are also other reasons for abandoning that condition. I distinguish between formal ad hocness, which is bad in the probabilistic sense that it results in disconfirmation of H, and argumentative ad hocness, which actually involves bad reasoning on the part of a subject. The latter is what I call “not counting the cost.” This distinction allows us to see why the 0.5 condition appeared attractive in the first place. The concept of not counting the cost also has implications for other areas of research, including both a Bayesian concept of unfalsifiability and the classic epistemological question of the problem of the external world.


Ad hocness Ad hoc hypotheses Bayesianism Disconfirmation 


  1. Adams, J. C. (1896) The scientific papers of John Couch Adams, Vol. 1, W. G. Adams, ed. Reprint: Hong Kong: Forgotten Books, 2013.Google Scholar
  2. Hempel, C. (1966). Philosophy of natural science. Englewood Cliffs, NJ: Prentice Hall.Google Scholar
  3. Horwich, P. (1982). Probability and evidence. Cambridge: Cambridge University Press.Google Scholar
  4. Howson, C., & Urbach, P. (1989). Scientific reasoning: The Bayesian approach (1st ed.). La Salle, IL: Open Court.Google Scholar
  5. Howson, C., & Urbach, P. (1993). Scientific reasoning: The Bayesian approach (2nd ed.). La Salle, IL: Open Court.Google Scholar
  6. Leslie, J. (1989). Universes. London: Routledge.Google Scholar
  7. McGrew, T. (1995). The foundations of knowledge. Lanham, MD: Littlefield Adams.Google Scholar
  8. McGrew, L. (2005). Likelihoods, multiple universes, and epistemic context. Philosophia Christi, 7, 475–481.Google Scholar
  9. McGrew, L. (2010). Probability kinematics and probability dynamics. Journal of Philosophical Research, 35, 89–104.CrossRefGoogle Scholar
  10. McGrew, T., & McGrew, L. (2009). The argument from miracles: A cumulative case for the resurrection of Jesus of Nazareth. In W. L. Craig & J. P. Moreland (Eds.), The Blackwell companion to natural theology (pp. 593–662). Oxford: Wiley-Blackwell.CrossRefGoogle Scholar
  11. Salmon, W. (1990). Rationality and objectivity in science or Tom Kuhn meets Tom Bayes. In C. Wade Savage (Ed.), Scientific theories, volume 14, Minnesota Studies in the Philosophy of Science (pp. 175–204). Minneapolis, MN: University of Minnesota Press.Google Scholar
  12. Scott, S. (2007) Invoking the Tooth Fairy twice, or how to identify cases of ad hoc hypothesis acceptance. PhD dissertation, University of North Carolina, Chapel Hill.Google Scholar
  13. Smart, W. M. (1947). John Couch Adams and the discovery of Neptune. Popular Astronomy, 55, 301–311.Google Scholar
  14. Strevens, M. (2001). The Bayesian treatment of auxiliary hypotheses. British Journal for the Philosophy of Science, 52, 515–537.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.KalamazooUSA

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