display all the ideas for this combination of texts
4 ideas
| 13288 | Consequence is truth-preserving, either despite substitutions, or in all interpretations [Koslicki] |
| Full Idea: Two conceptions of logical consequence: a substitutional account, where no substitution of non-logical terms for others (of the right syntactic category) produce true premises and false conclusions; and model theory, where no interpretation can do it. | |
| From: Kathrin Koslicki (The Structure of Objects [2008], 9.3.2 n8) | |
| A reaction: [compressed] |
| 14506 | 'Roses are red; therefore, roses are colored' seems truth-preserving, but not valid in a system [Koslicki] |
| Full Idea: 'Roses are red; therefore, roses are colored' may be necessarily truth-preserving, but it would not be classified as logically valid by standard systems of logic. | |
| From: Kathrin Koslicki (The Structure of Objects [2008], 9.3.2) |
| 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. |
| 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. |