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18121 | In logic a proposition means the same when it is and when it is not asserted [Bostock] |
Full Idea: In Modus Ponens where the first premise is 'P' and the second 'P→Q', in the first premise P is asserted but in the second it is not. Yet it must mean the same in both premises, or it would be guilty of the fallacy of equivocation. | |
From: David Bostock (Philosophy of Mathematics [2009], 7.2) | |
A reaction: This is Geach's thought (leading to an objection to expressivism in ethics, that P means the same even if it is not expressed). |