 A third challenge directed again especially, or even exclusively, at non-eliminative structuralism concerns the following. From a structuralist point of view, positions are always “positions in a structure”; i.e., the structure is primary and the positions are secondary. Hence, a particular mathematical object, such as the natural number 2, seems “ontologically dependent” on the background structure, here the structure of the natural numbers. (The fact that for a structuralist it is misguided to consider the number 2 as existing in itself reflects this aspect. It also illustrates a main difference between structuralism and logicism or set-theoretic foundationalism.) But how should this ontological dependence be understood? Are there perhaps connections to “grounding” or related notions in current analytic metaphysics? In this context too, many open questions remain and a lively debate has started (cf. Linnebo 2008, also, e.g., MacBride 2005 and Wigglesworth 2018). 