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Ideas for 'Parmenides', 'Letters from a Stoic' and 'Reason, Truth and History'

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5. Theory of Logic / J. Model Theory in Logic / 2. Isomorphisms
If cats equal cherries, model theory allows reinterpretation of the whole language preserving truth [Putnam]
     Full Idea: If the number of cats happens to equal the cherries, then it follows from the theory of models that there is a reinterpretation of the entire language that leaves all sentences unchanged in truth value while permuting the extensions of 'cat' and 'cherry'.
     From: Hilary Putnam (Reason, Truth and History [1981], Ch.2)
     A reaction: This horrifying result seems to come simply from the fact that there is an isomorphism between two models, which in turn seems to rest largely on the cardinality of the models. There seems to be something wrong with model theory here (?).