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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. |
| 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. |
| 23066 | Negation doesn't arise from reasoning, but from deep instincts [Cioran] |
| Full Idea: Negation never proceeds from reasoning but from something much more obscure and old. Arguments come afterward, to justify and sustain it. Every no rises out of the blood. | |
| From: E.M. Cioran (The Trouble with Being Born [1973], 02) | |
| A reaction: Music to my ears. In the Fregean era no one is allowed to talk about the origins of logical relations in the universal facts of physical existence. You can watch dogs saying no. |