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Ideas for 'fragments/reports', 'works' and 'Aenesidemus'

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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

13455	Frege did not think of himself as working with sets [Frege, by Hart,WD]
	Full Idea: Frege did not think of himself as working with sets.
	From: report of Gottlob Frege (works [1890]) by William D. Hart - The Evolution of Logic 1
	A reaction: One can hardly blame him, given that set theory was only just being invented.

4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set

16895	The null set is indefensible, because it collects nothing [Frege, by Burge]
	Full Idea: Frege regarded the null set as an indefensible entity from the point of view of iterative set theory. It collects nothing.
	From: report of Gottlob Frege (works [1890]) by Tyler Burge - Frege on Apriority (with ps) 2
	A reaction: The null set defines the possibility that something could be collected. At the very least, it introduces curly brackets into the language.

4. Formal Logic / F. Set Theory ST / 5. Conceptions of Set / c. Logical sets

3328	Frege proposed a realist concept of a set, as the extension of a predicate or concept or function [Frege, by Benardete,JA]
	Full Idea: Contrary to Dedekind's anti-realism, Frege proposed a realist definition of a set as the extension of a predicate (or concept, or function).
	From: report of Gottlob Frege (works [1890]) by José A. Benardete - Metaphysics: the logical approach Ch.13