|Geach, Peter T.
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Content/Geach: if two sentences (sentence constructions) UVW and UXY as a whole have the same content, it does not mean that U in UVW and U in UXY has the same meaning!
(5) All cats are mortal - is equivalent to the following two sentences:
(6) All cats are a subclass of mortals -
(7) All cats are the same class as some (subclasses of) mortals.
Each is as plausible as the other one, but they cannot both be correct, i.e. both are false.
Logic Matters Oxford 1972