 The core of set-theoretic structuralism, as just described, is to choose one of several isomorphic systems as the pragmatic referent for “the natural numbers” (similarly for the real numbers etc.). In a sense, our talk of “the natural numbers”, then also of “the number 0”, “the number 1”, etc., is relative to this initial choice. This is seen as unproblematic because, no matter how we choose, we will get the same arithmetic theorems (because of the categoricity of the axiom system, which implies its semantic completeness). As background, we can again employ Zermelo-Fraenkel set theory. But we can also broaden the approach slightly by allowing for “atoms” or “urelements”, i.e., objects that are not sets. Thus, we can include Julius Caesar or some beer mug in our domain, with the consequence that either of them can “be” the number 2, say, in the sense of taking up the “2-position” in the model for arithmetic we choose to work with. Because of this feature, we will use “relativist structuralism” for this approach (cf. Reck &amp; Price 2000). It also seems fair to say that this position, particularly in its set-theoretic version, is accepted by many mathematicians, explicitly or implicitly.  In fact, it may be the most widely favored form of structuralism.