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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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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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8249
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Class membership is not transitive, unlike being part of a part of the whole [Lesniewski, by George/Van Evra]
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Full Idea:
Lesniewski distinguished the part-whole relationship from class membership. Membership is not transitive: if s is an element of t, and t of u, then s is not an element of u, whereas a part of a part is a part of the whole.
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From:
report of Stanislaw Lesniewski (works [1916]) by George / Van Evra - The Rise of Modern Logic 7
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A reaction:
If I am a member of a sports club, and my club is a member of the league, I am not thereby a member of the league (so clubs are classes, not wholes). This distinction is clearly fairly crucial in ontology.
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16698
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Days exist, and yet they seem to be made up of parts which don't exist [Burley]
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Full Idea:
I grant that a successive being is composed out of non-beings, as is clear of a day, which is composed of non-entities. Some part of this day is past and some future, and yet this day is.
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From:
Walter Burley (Commentary on 'Physics' [1325], III text 11,f.65rb), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 18.3
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A reaction:
The dilemma of Aristotle over time infected the scholastic attempt to give an account of successive entities. A day is a wonderfully elusive entity for a metaphysician.
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16690
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Unlike permanent things, successive things cannot exist all at once [Burley]
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Full Idea:
This is the difference between permanent and successive things: that a permanent thing exists all at once, or at least can exist all at once, whereas it is incompatible with a successive thing to exist all at once.
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From:
Walter Burley (Commentary on 'Physics' [1325], III txt 11,f.65rb), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 18.1
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A reaction:
Permanent things sound like what are now called 'three-dimensional' objects, but scholastic 'entia successiva' are not the same as spacetime 'worms' or collections of temporal stages.
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