 The language of this contrast (‘in’ a subject vs. ‘said of’ a subject) is peculiar to the Categories, but the idea seems to recur in other works as the distinction between accidental vs. essential predication. Similarly, in works other than the Categories, Aristotle uses the label ‘universals’ (ta katholou) for the things that are “said of many;” things that are not universal he calls ‘particulars’ (ta kath’ hekasta). Although he does not use these labels in the Categories, it is not misleading to say that the doctrine of the Categories is that each category contains a hierarchy of universals and particulars, with each universal being ‘said of’ the lower-level universals and particulars that fall beneath it. Each category thus has the structure of an upside-down  tree.[2]  At the top (or trunk) of the tree are the most generic items in that  category[3]  (e.g., in the case of the category of substance, the genus plant and the genus animal); branching below them are universals at the next highest level, and branching below these are found lower levels of universals, and so on, down to the lowest level universals (e.g., such infimae species as man and horse); at the lowest level—the leaves of the tree—are found the individual substances, e.g., this man, that horse, etc.