Combining Texts

Ideas for 'fragments/reports', 'Intro to 2nd ed of Principia Mathematica' and 'Metaphysics: the logical approach'

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5 ideas

4. Formal Logic / B. Propositional Logic PL / 1. Propositional Logic
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).
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / e. Axioms of PL
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.
4. Formal Logic / F. Set Theory ST / 1. Set Theory
3326 Set theory attempts to reduce the 'is' of predication to mathematics [Benardete,JA]
     Full Idea: Set theory offers the promise of a complete mathematization of the 'is' of predication.
     From: José A. Benardete (Metaphysics: the logical approach [1989], Ch.13)
3327 The set of Greeks is included in the set of men, but isn't a member of it [Benardete,JA]
     Full Idea: Set inclusion is sharply distinguished from set membership (as the set of Greeks is found to be included in, but not a member of, the set of men).
     From: José A. Benardete (Metaphysics: the logical approach [1989], Ch.13)
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / a. Axioms for sets
3335 The standard Z-F Intuition version of set theory has about ten agreed axioms [Benardete,JA, by PG]
     Full Idea: Zermelo proposed seven axioms for set theory, with Fraenkel adding others, to produce the standard Z-F Intuition.
     From: report of José A. Benardete (Metaphysics: the logical approach [1989], Ch.17) by PG - Db (ideas)