According to the traditional view of the Categories, the ten "categories" are the highest genera of beings. Each of them stands at the head of a tree-like division of the the items falling under it; this division is also sometimes called a "category". The metaphysical structure made up of these ten divisions is the "system of the categories". According to the traditional view, the system of the categories is very rigidly laid out. Not only is every being included in the structure, but every being has exactly one location. Each being is predicated essentially of those below it along the lines of division. Each being is related to those above it, if any, as a determination of them, and to those below it, if any, as a determinable. Because of these facts, the full analysis of the essence of any being can be gotten by stringing together the names of all the beings superior to it in the division, along with a final differentia. But this traditional view is very widely off the mark. We here present arguments for rejecting the traditional interpretation of the categories.
Morrison, Donald, "Ontological Structures in Aristotle" (1988). The Society for Ancient Greek Philosophy Newsletter. 373.