Dean Peters

Most contemporary proponents of scientific realism advocate some form of selective realism. One of the most prominent variants is the working posits view, which claims that the essential propositions of a successful theory are those that are involved in the actual derivations of predictions. In this paper, I offer a systematic examination of this view, surveying no fewer than six competing interpretations of it. I argue, however, that none is satisfactory. A general reason to reject the working posits view is that it focuses on individual successful derivations, as opposed to the empirical success of a theory as a whole. In response to this, I suggest an alternative positive view, which regards as essential those theoretical posits which “unify” a diverse or large collection of other posits.

Selective scientific realists disagree on which theoretical posits should be regarded as essential to the empirical success of a scientific theory. A satisfactory account of essentialness will show that the (approximate) truth of the selected posits adequately explains the success of the theory. Therefore, (a) the essential elements must be discernible prospectively; (b) there cannot be a priori criteria regarding which type of posit is essential; and (c) the overall success of a theory, or ‘cluster’ of propositions, not only individual derivations, should be explicable. Given these desiderata, I propose a “unification criterion” for identifying essential elements