 In most approaches, including Armstrong’s, the relevant properties and the relevant relation, if any, are conceived of as parts, or constituents, of the structural property in question, and thus their being involved in the latter is a parthood relation. For instance, hydrogen, oxygen and bonding are constituents of H2O. Moreover, the composition of structural properties is isomorphic to that of the complexes exemplifying them. These two theses characterize what Lewis (1986a) calls the “pictorial conception”. It is worth noting that structural properties differ from conjunctive properties such as human and musician, in that the constituents of the latter (i.e., human and musician) are instantiated by whatever entity exemplifies the conjunctive property (i.e., a human being who is also a musician), whereas the constituents of a structural property (e.g., hydrogen, oxygen and bonding) are not instantiated by the entities that instantiate it (e.g., H2O molecules).