Identity in Physics and Elsewhere

Is identity a fundamental concept? Of course, it all depends on what it takes for something to be fundamental. For the purposes of this paper, I will consider identity’s fundamentality as exhibiting four features, which, if satisfied, also provide four reasons to think that a fundamental concept is involved (see Bueno [2014]): (1) Identity is presupposed in every conceptual system; (2) it is required to characterize individuals; (3) it is not possible to define it, and (4) it is assumed for the intelligibility of quantification. But what exactly is identity? Is it a property, a relation, or something else altogether? How is it related to indiscernibility? Is it a logical, a metaphysical, a pragmatic concept? These are all important issues, and there is much to be said, and much has been said, about them. But in the present article, I will try to remain, as much as possible, neutral on the various possible answers to these questions. (I intend to return to them in future work. For some discussion, see Williams [1989].) In a recent paper, Décio Krause and Jonas Arenhart have challenged the very idea that identity is (or can be) fundamental, resisting each of the four reasons, listed above, that I offered in its support (Krause and Arenhart [2015]). In what follows, I will discuss the most significant of their complaints and provide a defense of the centrality⎯in fact, the fundamentality⎯of identity. Krause and Arenhart have raised a formidable challenge, and provided a variety of significant arguments for their case. Here I will only be able to focus on some of them. But I do plan to address the remaining ones in a companion paper.