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Conservativity/Extension/Language/Tonk/Brandom: pro conservative extension: if the rules are not inferentially conservative, they allow new material inferences and can change the contents that were associated with the old vocabulary - expressive logic/Brandom: requires that no new inferences that contain only old vocabulary are rendered appropriate (if they have not been previously).
E.g. "boche"/Dummett: non-conservative extension: statements that do contain the expression (!) could be inferred from others that do not contain the expression either - E.g. conclusion from German nationality to cruelty - BrandomVsDummett: this is not about non-conservativity: it only shows that the expression "boche" has a content which is not contained in the other expressions - e.g. the term "temperature" has also changed with the methods of measurement - it s not about the novelty of a concept, but about unwanted conclusions.
Especially the material content of concepts is lost when the conceptual content is identified with the truth-conditions.
Expressive Vernunft Frankfurt 2000
Begründen und Begreifen Frankfurt 2001