The controversy over universals has been revived, the parties being the same that clashed in Antiquity and the Middle Ages: realism, conceptualism, nominalism. The difference is that the universals referred to at present are neither "forms' nor "essences of things", nor are they Platonic ideas of concrete objects, but abstract entities of a special kind: sets of individuals, sets of sets of individuals, sets of sets of sets of individuals, etc., interpreted as objects which are essentially non-perceivable, extra-temporal and extra-spatial. Just as centuries ago, the realistic standpoint is that universals exist; the conceptualistic standpoint is that they exist in mente, but not extra mentem; and the nominalistic standpoint, in opposition to the other two trends, is that the existence of universals is firmly rejected. Conceptualism has few adherents at present; but the other two movements are very strong.