Abstract
In a recent paper McCain (2012) argues that weak predictivism creates an important challenge for external world scepticism. McCain regards weak predictivism as uncontroversial and assumes the thesis within his argument. There is a sense in which the predictivist literature supports his conviction that weak predictivism is uncontroversial. This absence of controversy, however, is a product of significant plasticity within the thesis, which renders McCain’s argument worryingly vague. For McCain’s argument to work he either needs a stronger version of weak predictivism than has been defended within the literature, or must commit to a more precise formulation of the thesis and argue that weak predictivism, so understood, creates the challenge to scepticism that he hopes to achieve. The difficulty with the former is that weak predictivism is not uncontroversial in the respect that McCain’s argument would require. I consider the prospects of saving McCain’s argument by committing to a particular version of weak predictivism, but find them unpromising for several reasons.
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Notes
Within this note I’ll concede this suggestion of McCain’s, although I suspect it’s less straightforward than he admits. For example, if sceptical hypotheses are offered as evidence that the content of my memories cannot be trusted, then it is unclear whether I can be sure that I predicted anything at all.
For an excellent introduction into the predictivist literature, see Barnes (2008).
Exactly how we are to distinguish predictions from accommodations is a matter for debate. McCain is not explicit, but I suspect he understands predictivism heuristically—what distinguishes predictions from accommodations is something about how each are used in the construction or development of a theory. Heuristic predictivism has emerged as the most influential version of predictivism within philosophy of science in recent years, so it is a reasonable version for McCain to adopt. My objections don’t rely on attributing to McCain this interpretation.
The concept of a severe test is central to Mayo’s ideas on confirmation.
Lipton identifies his own predictivist thesis as strong, rather than weak. On what has become the standard means of distinguishing strong from weak versions, however, Lipton’s qualifies only as a weak predictivist thesis.
McCain’s presentation of weak predictivism includes neither the observation that advocates for the thesis suggest only that predictive success is important in some circumstances, nor that distinct predictivist theses relate predictive success to different qualities.
Suppose, to illustrate, scientists A and B disagree about which of two rival hypotheses are best supported by available evidence. Scientist A notes a feature of one hypothesis that is not shared by the second hypothesis and appeals to this feature as reason to justify their ranking. Scientist B responds that this feature has no intrinsic value, for purposes of evaluating these particular hypotheses. It would be unsatisfying for A to concede the point but add that, nevertheless, this feature implies some further, unspecified, quality that does have evidentiary value. McCain commits the same mistake as scientist A.
An important advantage of predictions, for Barnes, is their implication that a competent judge must have good reasons if she predicts some outcome on the basis of a particular theory. Evaluators of that theory who are unsure of its merits might regard the competent predictor’s endorsement of the predictions as evidence for evidence, i.e. evidence that there are further reasons (albeit unknown to the evaluator) for being favourably disposed towards the theory. The evaluator might therefore increase their degree of confidence in the theory. If the significance of the predictions of CS is to be understood in the same terms, however, then the sceptic must be ignorant of reasons that we possess for making certain predictions. But in this case the burden is clearly on us to point out the reasons themselves for our confidence in CS, rather than relying on an indirect argument that because we predict certain experiences we probably have good reasons for doing so.
There is again here the suspicion that McCain is guilty of conflating strong and weak predictivist theses. If predictive success is evidence that the successful theory is better confirmed than empirical equivalents that accommodate data, then McCain’s argument works. However, this is stronger than weak predictivism as it is typically understood. If predictivism is evidence of further considerations that are themselves epistemically relevant, then McCain owes an explanation for why we can’t evaluate those considerations directly, in the case of CS.
See Barnes (2008, pp. 98–9).
Barnes distinguishes virtuous from unvirtuous predictors. His analysis of unvirtuous predictors is similar, as he acknowledges, to Lipton’s fudging explanation, so I’ll focus here on his original contributions concerning virtuous predictors.
References
Barnes, E. (2008). The paradox of predictivism. Cambridge University Press.
Harker, D. (2008). On the predilections for predictions. British Journal for the Philosophy of Science, 59, 429–53.
Hitchcock, C., & Sober, E. (2004). Prediction versus accommodation and the risk of overfitting. British Journal for the Philosophy of Science, 55, 1–34.
Huemer, M. (2000). Direct realism and the brain-in-a-vat argument. Philosophy and Phenomenological Research, 61, 397–413.
Lange, M. (2001). The apparent superiority of prediction to accommodation. British Journal for the Philosophy of Science, 52, 575–588.
Lipton, P. (2004). Inference to the best explanation (2nd ed.). London: Routledge.
Mayo, D. (1996). Error and the growth of experimental knowledge. Chicago: University of Chicago Press.
McCain, K. (2012). A predictivist argument against scepticism. Analysis, 72, 660–665.
Acknowledgments
My thanks to two anonymous referees from this journal for helpful comments on an earlier draft.
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Harker, D.W. Discussion Note: McCain on Weak Predictivism and External World Scepticism. Philosophia 41, 195–202 (2013). https://doi.org/10.1007/s11406-012-9409-y
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DOI: https://doi.org/10.1007/s11406-012-9409-y