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Ideas for 'Necessary Existents', 'Vagueness and Contradiction' and 'The philosophical basis of intuitionist logic'

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5 ideas

5. Theory of Logic / D. Assumptions for Logic / 1. Bivalence
No attempt to deny bivalence has ever been accepted [Sorensen]
     Full Idea: The history of deviant logics is without a single success. Bivalence has been denied at least since Aristotle, yet no anti-bivalent theory has ever left the philosophical nursery.
     From: Roy Sorensen (Vagueness and Contradiction [2001], Intro)
     A reaction: This is part of a claim that nothing in reality is vague - it is just our ignorance of the truth or falsity of some propositions. Personally I don't see why 'Grandad is bald' has to have a determinate truth value.
5. Theory of Logic / E. Structures of Logic / 4. Variables in Logic
We now see that generalizations use variables rather than abstract entities [Sorensen]
     Full Idea: As philosophers gradually freed themselves from the assumption that all words are names, ..they realised that generalizations really use variables rather than names of abstract entities.
     From: Roy Sorensen (Vagueness and Contradiction [2001], 8.4)
     A reaction: This looks like a key thought in trying to understand abstraction - though I don't think you can shake it off that easily. (For all x)(x-is-a-bird then x-has-wings) seems to require a generalised concept of a bird to give a value to the variable.
5. Theory of Logic / G. Quantification / 1. Quantification
Classical quantification is an infinite conjunction or disjunction - but you may not know all the instances [Dummett]
     Full Idea: Classical quantification represents an infinite conjunction or disjunction, and the truth-value is determined by the infinite sum or product of the instances ....but this presupposes that all the instances already possess determinate truth-values.
     From: Michael Dummett (The philosophical basis of intuitionist logic [1973], p.246)
     A reaction: In the case of the universal quantifier, Dummett is doing no more than citing the classic empiricism objection to induction - that you can't make the universal claim if you don't know all the instances. The claim is still meaningful, though.
5. Theory of Logic / L. Paradox / 3. Antinomies
Denying problems, or being romantically defeated by them, won't make them go away [Sorensen]
     Full Idea: An unsolvable problem is still a problem, despite Wittgenstein's view that there are no genuine philosophical problems, and Kant's romantic defeatism in his treatment of the antinomies of pure reason.
     From: Roy Sorensen (Vagueness and Contradiction [2001], 4.3)
     A reaction: I like the spin put on Kant, that he is a romantic in his defeatism. He certainly seems reluctant to slash at the Gordian knot, e.g. by being a bit more drastically sceptical about free will.
5. Theory of Logic / L. Paradox / 6. Paradoxes in Language / a. The Liar paradox
Banning self-reference would outlaw 'This very sentence is in English' [Sorensen]
     Full Idea: The old objection to the ban on self-reference is that it is too broad; it bans innocent sentences such as 'This very sentence is in English'.
     From: Roy Sorensen (Vagueness and Contradiction [2001], 11.1)
     A reaction: Tricky. What is the sigificant difference between 'this sentence is in English' and 'this sentence is a lie'? The first concerns context and is partly metalinguistic. The second concerns semantics and truth. Concept and content..