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Ideas for 'fragments/reports', 'Friendship' and 'Summa Theologicae'

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2 ideas

5. Theory of Logic / B. Logical Consequence / 1. Logical Consequence

23173	If a syllogism admits one absurdity, others must follow [Aquinas]
	Full Idea: In syllogistic arguments, granted one absurdity, others must follow too.
	From: Thomas Aquinas (Summa Theologicae [1265], I-II Q19 6)
	A reaction: This asserts the necessity of logical consequence, which he derives from Aristotle.

5. Theory of Logic / B. Logical Consequence / 5. Modus Ponens

8078	Modus ponens is one of five inference rules identified by the Stoics [Chrysippus, by Devlin]
	Full Idea: Modus ponens is just one of the five different inference rules identified by the Stoics.
	From: report of Chrysippus (fragments/reports [c.240 BCE]) by Keith Devlin - Goodbye Descartes Ch.2
	A reaction: Modus ponens strikes me as being more like a definition of implication than a 'rule'. Implication is what gets you from one truth to another. All the implications of a truth must also be true.