display all the ideas for this combination of texts
4 ideas
| 8077 | Stoic propositional logic is like chemistry - how atoms make molecules, not the innards of atoms [Chrysippus, by Devlin] |
| Full Idea: In Stoic logic propositions are treated the way atoms are treated in present-day chemistry, where the focus is on the way atoms fit together to form molecules, rather than on the internal structure of the atoms. | |
| From: report of Chrysippus (fragments/reports [c.240 BCE]) by Keith Devlin - Goodbye Descartes Ch.2 | |
| A reaction: A nice analogy to explain the nature of Propositional Logic, which was invented by the Stoics (N.B. after Aristotle had invented predicate logic). |
| 20791 | Chrysippus has five obvious 'indemonstrables' of reasoning [Chrysippus, by Diog. Laertius] |
| Full Idea: Chrysippus has five indemonstrables that do not need demonstration:1) If 1st the 2nd, but 1st, so 2nd; 2) If 1st the 2nd, but not 2nd, so not 1st; 3) Not 1st and 2nd, the 1st, so not 2nd; 4) 1st or 2nd, the 1st, so not 2nd; 5) 1st or 2nd, not 2nd, so 1st. | |
| From: report of Chrysippus (fragments/reports [c.240 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 07.80-81 | |
| A reaction: [from his lost text 'Dialectics'; squashed to fit into one quote] 1) is Modus Ponens, 2) is Modus Tollens. 4) and 5) are Disjunctive Syllogisms. 3) seems a bit complex to be an indemonstrable. |
| 8309 | A set is a 'number of things', not a 'collection', because nothing actually collects the members [Lowe] |
| Full Idea: A set is 'a number of things', not a 'collection'. Nothing literally 'collects' the members of a set, such as the set of planets of the sun, unless it be a Fregean 'concept' under which they fall. | |
| From: E.J. Lowe (The Possibility of Metaphysics [1998], 10.6) | |
| A reaction: I'm tempted to say that the sun has collected a set of planets (they're the ones that rotate around it). Why can't we have natural sets, which have been collected by nature? A question of the intension, as well as the extension.... |
| 8322 | I don't believe in the empty set, because (lacking members) it lacks identity-conditions [Lowe] |
| Full Idea: It is not clear to me that the empty set has well-defined identity-conditions. A set has these only to the extent that its members do - but the empty set has none. | |
| From: E.J. Lowe (The Possibility of Metaphysics [1998], 12.3 n8) | |
| A reaction: The empty set is widely used by those who base their metaphysics of maths on sets. It defines zero, and hence is the starting poing for Peano's Postulates (Idea 5897). It might not have identity in itself, but you know where you have arrived after 2 - 2. |