 There are two sorts of substance: a primary substance is, e.g., an individual man or horse; the species (and genera) of these individuals (e.g., man, animal) are secondary substances. While the ten categories are all equally highest kinds, primary substances nonetheless have a certain sort of priority, since “all the other things are either said of the primary substances as subjects or in them as subjects. So if the primary substances did not exist it would be impossible for any of the other things to exist” (Categories 2b4).