 The individuals in the category of substance play a special role in this scheme. Aristotle calls them “primary substances” (prôtai ousiai) for without them, as he says, nothing else would exist. Indeed, Aristotle offers an argument (2a35–2b7) to establish the primary substances as the fundamental entities in this ontology. Everything that is not a primary substance, he points out, stands in one of the two relations (inhering ‘in’, or being ‘said of’) to primary substances. A genus, such as animal, is ‘said of’ the species below it and, since they are ‘said of’ primary substances, so is the genus (recall the transitivity of the ‘said of’ relation). Thus, everything in the category of substance that is not itself a primary substance is, ultimately, ‘said of’ primary substances. And if there were no primary substances, there would be no “secondary” substances (species and genera), either. For these secondary substances are just the ways in which the primary substances are fundamentally classified within the category of substance. As for the members of non-substance categories, they too depend for their existence on primary substances. A universal in a non-substance category, e.g., color, in the category of quality, is ‘in’ body, Aristotle tells us, and therefore in individual bodies. For color could not be ‘in’ body, in general, unless it were ‘in’ at least some particular bodies. Similarly, particulars in non-substance categories (although there is not general agreement among scholars about what such particulars might be) cannot exist on their own. E.g., a determinate shade of color, or a particular and non-shareable bit of that shade, is not capable of existing on its own—if it were not ‘in’ at least some primary substance, it would not exist. So primary substances are the basic entities—the basic “things that there are”—in the world of the Categories.