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Ideas for 'fragments/reports', 'Mr Strawson on Logical Theory' and 'Dialogue on human freedom and origin of evil'

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4 ideas

4. Formal Logic / B. Propositional Logic PL / 1. Propositional Logic
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 / a. Symbols of PL
The logician's '→' does not mean the English if-then [Quine]
     Full Idea: The logician drops 'if-then' in favour of '→' without ever entertaining the mistaken idea that they are synonymous.
     From: Willard Quine (Mr Strawson on Logical Theory [1953], V)
     A reaction: [Quine uses the older horseshoe symbol] The conditional in English is not well understood, whereas the symbol is unambiguous. A warning to myself, since I have a tendency to translate symbols into English all the time. [p.156 'implies' is worse!]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / e. Axioms of PL
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 / D. Modal Logic ML / 6. Temporal Logic
It is important that the quantification over temporal entities is timeless [Quine]
     Full Idea: It would be hard to exaggerate the importance of recognising the timelessness of quantification over temporal entities.
     From: Willard Quine (Mr Strawson on Logical Theory [1953], IV)
     A reaction: 'Some moments in this cricket match were crucial'. The domain is not timeless, but consists of moments in this match. Can you say the quantifier is timeless but its domain is not? Only in the sense that 'very' is a timeless word, I think.