9390
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Logic guides thinking, but it isn't a substitute for it [Rumfitt]
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Full Idea:
Logic is part of a normative theory of thinking, not a substitute for thinking.
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From:
Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.13)
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A reaction:
There is some sort of logicians' dream, going back to Leibniz, of a reasoning engine, which accepts propositions and outputs inferences. I agree with this idea. People who excel at logic are often, it seems to me, modest at philosophy.
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15537
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If cats are vague, we deny that the many cats are one, or deny that the one cat is many [Lewis]
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Full Idea:
To deny that there are many cats on the mat (because removal of a few hairs seems to produce a new one), we must either deny that the many are cats, or else deny that the cats are many. ...I think both alternatives lead to successful solutions.
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From:
David Lewis (Many, but almost one [1993], 'The paradox')
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A reaction:
He credits the problem to Geach (and Tibbles), and says it is the same as Unger's 'problem of the many' (Idea 15536).
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9389
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Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt]
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Full Idea:
Vagueness in respect of membership is consistency with determinacy of the set's identity, so long as a set's identity is taken to consist, not in its having such-and-such members, but in its being the extension of a concept.
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From:
Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.5)
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A reaction:
I find this view of sets much more appealing than the one that identifies a set with its members. The empty set is less of a problem, as well as non-existents. Logicians prefer the extensional view because it is tidy.
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15539
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Basic to pragmatics is taking a message in a way that makes sense of it [Lewis]
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Full Idea:
The cardinal principle of pragmatics is that the right way to take what is said, if at all possible, is the way that makes sense of the message.
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From:
David Lewis (Many, but almost one [1993], 'A better solution')
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A reaction:
Thus when someone misuses a word, suggesting nonsense, we gloss over it, often without even mentioning it, because the underlying sense is obvious. A good argument for the existence of propositions. Lewis doesn't mention truth.
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