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Ideas for 'fragments/reports', 'On the Moral and Legal State of Abortion' and 'Mere Possibilities'

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4 ideas

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.

5. Theory of Logic / D. Assumptions for Logic / 2. Excluded Middle

6023	Every proposition is either true or false [Chrysippus, by Cicero]
	Full Idea: We hold fast to the position, defended by Chrysippus, that every proposition is either true or false.
	From: report of Chrysippus (fragments/reports [c.240 BCE]) by M. Tullius Cicero - On Fate ('De fato') 38
	A reaction: I am intrigued to know exactly how you defend this claim. It may depend what you mean by a proposition. A badly expressed proposition may have indeterminate truth, quite apart from the vague, the undecidable etc.

5. Theory of Logic / E. Structures of Logic / 1. Logical Form

16464	We regiment to get semantic structure, for evaluating arguments, and understanding complexities [Stalnaker]
	Full Idea: The point of regimentation is to give a perspicuous representation of the semantic structure of an expression, making it easier to evaluate the validity of arguments and to interpret complex statements.
	From: Robert C. Stalnaker (Mere Possibilities [2012], 4.2)
	A reaction: This is an authoritative summary from an expert of why all philosophers must take an interest in logical form.

5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / e. or

16465	In 'S was F or some other than S was F', the disjuncts need S, but the whole disjunction doesn't [Stalnaker]
	Full Idea: In 'either Socrates was a philosopher or someone other than Socrates was a philosopher', both propositions expressed by the disjuncts depend for their existence on the existence of Socrates, but the whole disjunction does not.
	From: Robert C. Stalnaker (Mere Possibilities [2012], 4.2)
	A reaction: Nice example, just the sort of thing we pay philosophers to come up with. He is claiming that propositions can exist in possible worlds in which the individuals mentioned do not exist.