9463
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Classical logic is bivalent, has excluded middle, and only quantifies over existent objects [Jacquette]
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Full Idea:
Classical logic (of Whitehead, Russell, Gödel, Church) is a two-valued system of propositional and predicate logic, in which all propositions are exclusively true or false, and quantification and predication are over existent objects only.
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From:
Dale Jacquette (Intro to I: Classical Logic [2002], p.9)
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A reaction:
All of these get challenged at some point, though the existence requirement is the one I find dubious.
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14182
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If the logic of 'taller of' rests just on meaning, then logic may be the study of merely formal consequence [Read]
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Full Idea:
In 'A is taller than B, and B is taller than C, so A is taller than C' this can been seen as a matter of meaning - it is part of the meaning of 'taller' that it is transitive, but not of logic. Logic is now seen as the study of formal consequence.
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From:
Stephen Read (Formal and Material Consequence [1994], 'Reduct')
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A reaction:
I think I find this approach quite appealing. Obviously you can reason about taller-than relations, by putting the concepts together like jigsaw pieces, but I tend to think of logic as something which is necessarily implementable on a machine.
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14184
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In modus ponens the 'if-then' premise contributes nothing if the conclusion follows anyway [Read]
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Full Idea:
A puzzle about modus ponens is that the major premise is either false or unnecessary: A, If A then B / so B. If the major premise is true, then B follows from A, so the major premise is redundant. So it is false or not needed, and contributes nothing.
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From:
Stephen Read (Formal and Material Consequence [1994], 'Repres')
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A reaction:
Not sure which is the 'major premise' here, but it seems to be saying that the 'if A then B' is redundant. If I say 'it's raining so the grass is wet', it seems pointless to slip in the middle the remark that rain implies wet grass. Good point.
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14186
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Logical connectives contain no information, but just record combination relations between facts [Read]
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Full Idea:
The logical connectives are useful for bundling information, that B follows from A, or that one of A or B is true. ..They import no information of their own, but serve to record combinations of other facts.
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From:
Stephen Read (Formal and Material Consequence [1994], 'Repres')
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A reaction:
Anyone who suggests a link between logic and 'facts' gets my vote, so this sounds a promising idea. However, logical truths have a high degree of generality, which seems somehow above the 'facts'.
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