The controversy over universals has been revived, the parties being the same clashed in Antiquity and the Middle Ages: realism, conceptualism, nominalism. The difference is that universals referred to at present neither "forms' "essence of things' nor are they Platonic ideas of concrete objects, but abstract entities of a special kind: set of individuals, sets of sets individuals, sets of sets of sets of individuals, etc., interpreted as objects which are essentially non-perceivable, extra-temporal and extra-spatial.