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Ideas for 'fragments/reports', 'Truth and Truthmakers' and 'Maxims'

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4 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
18396 The set theory brackets { } assert that the member is a unit [Armstrong]
     Full Idea: The idea is that braces { } attribute to an entity the place-holding, or perhaps determinable, property of unithood.
     From: David M. Armstrong (Truth and Truthmakers [2004], 09.5)
     A reaction: I like this. There is Socrates himself, then there is my concept , and then there is the singleton {Socrates}. Those braces must add something to the concept. You can't add braces to Socrates himself.
4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set
18393 For 'there is a class with no members' we don't need the null set as truthmaker [Armstrong]
     Full Idea: The null class is useful in formal set theory, but I hope that does not require that there be a thing called the null class which is truthmaker for the strange proposition .
     From: David M. Armstrong (Truth and Truthmakers [2004], 09.1)
     A reaction: It is not quite clear why it doesn't, but then it is not quite clear to philosophers what the status of the null set is, in comparison with sets that have members.