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Class/set/ / Prior: the statement that something is a member of a class is only seemingly a sentence about classes - in reality it is nothing more and nothing less than to say that "x f-s". - the appearance of the existence of "x" and of the existence of classes disappears - Clases are only logical construtions - only then the identity of unicorns and Pegasi is harmless (via the empty set) -
Logical constructions are no entities: all classes are logical constructions.
Objects of thought Oxford 1971
Arthur N. Prior
Papers on Time and Tense 2nd Edition Oxford 2003