  Ockham employs a number of distinctions in the exposition of his account. One of these is particularly important for subsequent authors. This is the distinction between “category” taken as one of the ten highest genera (e.g., substance, quantity, quality, etc.) and “category” taken as the set of coordinated predicates contained in each of these genera. In the former sense, the term ‘category’ refers to each of the ten highest genera, whereas in the latter sense, the term refers to any set of predicates ordered to one another. The most famous example of the latter is Porphyry's tree, which starts out with “substance” at the top and includes in descending order such items as “corporeal,” “living,” “animal,” and “man.” In the Summa logicae, Ockham presents the distinction as follows: