Of this view the part which was not Aristotle's, the state of " universalia ante rem," was due to the Neoplatonists, who interpreted the " separate forms " of Plato to be ideas in intellect, and handed down their interpretation through St Augustine to the medieval Realists like Aquinas, who thus combined Neoplatonism with Aristotelianism.
The controversy between nominalists and realists arose from a passage in Boethius' translation of Porphyry's Introduction to the Categories of Aristotle, which propounded the problem of genera and species, (1) as to whether they subsist in themselves or only in the mind; (2) whether, if subsistent, they are corporeal or incorporeal; and (3) whether separated from sensible things or placed in them.
The Realists held that universals alone have substantial reality, existing ante res; the Nominalists that universals are mere names invented to express the qualities of particular things and existing post res; while the Conceptualists, mediating between the two extremes, held that universals are concepts which exist in our minds and express real similarities in things themselves.
The controversy was between Nominalists and Realists; and, exclusively logical as the point may at first sight seem to be, adherence to one side or the other is an accurate indication of philosophic tendency.
The Realists, he considers, have greatly sinned against this maxim in their theory of a real universal or common element in all the individuals of a class.