Generally, categories are understood to express the most general features of reality. Yet, since categories have this special status, obtaining a correct list of them is difficult. This question is addressed by examining how Thomas Aquinas establishes the list of categories through a technique of identifying diversity in how predicates are per se related to their subjects. A sophisticated critique by Duns Scotus of this position is also examined, a rejection which is fundamentally grounded in the idea that no real distinction can be made from a logical one. It is argued Aquinas's approach...