  Many structuralists are motivated by the thought that if mathematics describes its domain only up to isomorphism, if in other words, it only describes the structure of the domain, once the scientific description of the world becomes largely mathematical, then scientific knowledge too becomes structural knowledge. However, it may then be argued that if only the structure of mathematical theories is relevant to ontology in mathematics, and only structural aspects of the mathematical formalism of physical theories are relevant to ontology in physics, then there is nothing to distinguish physical and mathematical structure. Van Fraassen argues that the heart of the problem with OSR is this: