ABSTRACT. Reichenbach writes that the physical object cannot be determined by axioms and definitions: it is a thing of the real world, not an object of the logical world of mathematics. Preece and Stoddart claim that self-assembly deals with the construction of discrete molecular and supramolecular assemblies that have programmed into them a way by which the architecture and function can be controlled. Gooding provides an account of how visual models mediate between the interpretation of source data and the explanation of such data.