Structuralism is a view about the subject matter of mathematics according to which what matters are structural relationships in abstraction from the intrinsic nature of the related objects. Mathematics is seen as the free exploration of structural possibilities, primarily through creative concept formation, postulation, and deduction. The items making up any particular system exemplifying the structure in question are of no importance; all that matters is that they satisfy certain general conditions—typically spelled out in axioms defining the structure or structures of interest—characteristic of the branch of mathematics in question. Thus, in the basic case of arithmetic, the famous "axioms" of Richard Dedekind (taken over by Giuseppe Peano, as he acknowledged) were conditions in a definition of a "simply infinite system," with an initial item, each item having a unique next one, no two with the same next one, and all items finitely many...