Chris Mitsch

Logical inferentialists have expected identity to be susceptible of harmonious introduction and elimination rules in natural deduction. While Read and Klev have proposed rules they argue are harmonious, Griffiths and Ahmed have criticized these rules as insufficient for harmony. These critics, moreover, suggest that no harmonious rules are forthcoming. We argue that these critics are correct: the logical inferentialist should abandon hope for harmonious rules for identity. The paper analyzes the three major uses of identity in presumed-logical languages: variable coordination, definitional substitution, and co-reference. We show that identity qua variable coordination is not logical by providing a harmonious natural-deduction system that captures this use through the quantifiers. We then argue that identity qua definitional substitution or co-reference faces a dilemma: either its rules are harmonious but they obscure its actual use in inference, or its rules are not harmonious but they make its actual use in inference plain. We conclude that the inferentialist may have harmonious rules for identity only by disrespecting its inferential use.

Haag’s theorem cries out for explanation and critical assessment: It sounds the alarm that something is (perhaps) not right in one of the standard ways of constructing interacting fields to be used in generating predictions for scattering experiments. Viewpoints as to the precise nature of the problem, the appropriate solution, and subsequently-called-for developments in areas of physics, mathematics, and philosophy differ widely. In this paper, we develop and deploy a conceptual framework for critically assessing these disparate responses to Haag’s theorem. Doing so reveals the driving force of more general questions as to the nature and purpose of foundational work in physics.

Some understand Stein’s “Yes, but…” as an entry in the realism—instrumentalism debate (RID) itself, albeit one dissatisfied with then-extant positions. In this paper, however, I argue the opposite: Stein’s conception of science and his approach to its history and philosophy actually preclude the RID. First, I characterize Stein as persistently attending to his own historical and philosophical methods. I then describe his conception of science as both a dialectic and an enterprise, and I draw from this conception several conclusions about the relations between science and its history and philosophy. Finally, I provide a reading of “Yes, but…” that follows from Stein’s conception of science. On this reading, the RID is either irrelevant to or wrong of science and, moreover, distracts from a legitimate inquiry. I conclude by interpreting Stein’s remark that there is ``no difference that makes a difference’’ between a cogent and enlightened realism and a sophisticated instrumentalism.