Reichenbach, Reference Classes, and Single Case ‘Probabilities’

Abstract

Perhaps the most difficult problem confronted by Reichenbach’s explication of physical probabilities as limiting frequencies is that of providing decision procedures for assigning singular occurrences to appropriate reference class, i.e., the problem of the single case.¹ Presuming the symmetry of explanations and predictions is not taken for granted, this difficulty would appear to have two (possibly non-distinct) dimensions, namely: the problem of selecting appropriate reference classes for predicting singular occurrences, i.e., the problem of (single case) prediction, and the problem of selecting appropriate reference classes for explaining singular occurrences, i.e., the problem of (single case) explanation. If the symmetry thesis is theoretically sound, then these aspects of the problem of the single case are actually non-distinct, since any singular occurrence should be assigned to one and the same reference class for purposes of either kind; but if it is not the case that singular occurrences should be assigned to one and the same reference class for purposes of either kind, then these aspects are distinct and the symmetry thesis is not sound.²

The author is grateful to Wesley C. Salmon for his valuable criticism of an earlier version of this paper.