Since the Isagoge of Porphyry universals have
generally been ranged under the five heads of genus, differentia,
species, property, and accident, called in the title of his book the
five φωναί, but in subsequent times more usually the five predicables.
Aristotle, treating of the same subject, recognises only four. The
question whether genus and species have independent reality is declined
by Porphyry, but became the great philosophical controversy of the
Middle Ages, that, under various subordinate aspects, of nominalism and