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3 ideas
16728 | Logicians acknowledge too few things, while others acknowledge too many [Fitzralph] |
Full Idea: Those who have been well trained in logic err in recognising too few things, whereas others who are ignorant of logic ascribe to every statement a new entity, postulating more entities than God has ever established as real. | |
From: Richard Fitzralph (Sentences [1328], II.1.2), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 22.3 |
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. |