display all the ideas for this combination of texts
3 ideas
8078 | Modus ponens is one of five inference rules identified by the Stoics [Chrysippus, by Devlin] |
Full Idea: Modus ponens is just one of the five different inference rules identified by the Stoics. | |
From: report of Chrysippus (fragments/reports [c.240 BCE]) by Keith Devlin - Goodbye Descartes Ch.2 | |
A reaction: Modus ponens strikes me as being more like a definition of implication than a 'rule'. Implication is what gets you from one truth to another. All the implications of a truth must also be true. |
6163 | If bivalence is rejected, then excluded middle must also be rejected [Rowlands] |
Full Idea: If you reject the principle of bivalence (that a proposition is either determinately true or false), then statements are also not subject to the Law of Excluded Middle (P or not-P). | |
From: Mark Rowlands (Externalism [2003], Ch.3) | |
A reaction: I think Rowlands is wrong about this. Excluded Middle could be purely syntacti, or its semantics could be 'True or Not-True'. Only bivalent excluded middle introduces 'True or False'. Compare Idea 4752. |
6023 | Every proposition is either true or false [Chrysippus, by Cicero] |
Full Idea: We hold fast to the position, defended by Chrysippus, that every proposition is either true or false. | |
From: report of Chrysippus (fragments/reports [c.240 BCE]) by M. Tullius Cicero - On Fate ('De fato') 38 | |
A reaction: I am intrigued to know exactly how you defend this claim. It may depend what you mean by a proposition. A badly expressed proposition may have indeterminate truth, quite apart from the vague, the undecidable etc. |