What Elements of Successful Scientific Theories Are the Correct Targets for “Selective” Scientific Realism?

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