The Evidential Support Argument for Uniqueness

Jennifer Munt

In recent years there has been a small, but growing, literature emerge in response to Roger White’s (2005; 2010) defence of the Uniqueness thesis. Uniqueness holds that simply possessing a body of evidence completely determines what is rational to believe. This paper will examine the only positive argument given in support of Uniqueness: the evidential support argument (ESA). I will offer a comprehensive evaluation of this argument and consider one persuasive objection. This objection, given by Thomas Kelly against White, claims that rewriting ESA to reflect a commitment to a three-place evidential relation is inconsistent with the conclusion of the argument. Thus, Kelly argues, ESA presupposes a two-place evidential relation. Firstly, I will argue that a rational reconstruction of White’s views over a number of published papers can consistently affirm the evidential support argument with a three-place evidential relation that is relative to a uniquely determined prior probability distribution. Secondly, I will argue that the dispute between White and Kelly should be dramatically reframed from a disagreement on whether we should accept a two-place or three-place evidential relation, to a dispute that is motivated by a much broader debate in Bayesian epistemology concerning the permissibility of priors.