|Classes: identity of classes provided by same elements (extension) - identity of properties by the same predicates (intension).|
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Class/Wessel: "What is a class?": Wrong question, without circularity it can only be introduced as a logical operator - also circular as abstraction: requires individuals areas - concept of class and class logic superfluous, merely different representations of the concept of the propositional function and the classical QL - class of Amazons exists as an empty class - Def Class: if tA is a class term, then A is a class - Problem: left side burdened by existence, right side not - Solution: instead of identity only meaning equality of terms -
(t â‚¬s P(s) <=> t â‚¬s Q(s)) =def As(P(s) ↔ Q(s)) -thus a definition by abstraction becomes a mere facon de parler.
Logik Berlin 1999