Einstein's 1935 Letters to Schrödinger and Popper and the Boundaries of the PBR $ψ$-Epistemic Framework

Abstract: Einstein's 1935 critique of quantum mechanics is often associated with the Einstein-Podolsky-Rosen (EPR) argument, yet his private correspondence from that year reveals a more exact conceptual structure guiding his claim that the $ψ$-function is incomplete. This paper reconstructs Einstein's reasoning in his letters to Schrödinger and Popper and examines how it engages, and fails to engage with contemporary $ψ$-ontic/$ψ$-epistemic distinctions. Recent scholarship, most notably by Ben-Menahem, has interpreted Einstein as an early representative of the modern $ψ$-epistemic tradition within the Harrigan-Spekkens ontological models framework and the Pusey-Barrett-Rudolph (PBR) theorem. I argue, however, that this retrospective classification is undermined by Ben-Menahem's own distinction between realist and radical epistemic interpretations: Einstein's 1935 view lacks the structural assumptions - defined ontic state space, preparation distributions, and overlap structure - required for membership in the HS/PBR class of $ψ$-epistemic models. Any such identification, therefore, requires importing formal machinery foreign to Einstein's original argument.