The critics of Aquinas - Duns Scotus and the later Nominalists - show some tendency towards rational scepticism.
The latter position, ascribed by the schoolmen to the Averroists, becomes dominant among the later Nominalists, William of Occam and his disciples, who withdraw all doctrines of faith from the sphere of reason.
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.