15716
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If axioms and their implications have no contradictions, they pass my criterion of truth and existence [Hilbert]
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Full Idea:
If the arbitrarily given axioms do not contradict each other with all their consequences, then they are true and the things defined by the axioms exist. For me this is the criterion of truth and existence.
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From:
David Hilbert (Letter to Frege 29.12.1899 [1899]), quoted by R Kaplan / E Kaplan - The Art of the Infinite 2 'Mind'
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A reaction:
If an axiom says something equivalent to 'fairies exist, but they are totally undetectable', this would seem to avoid contradiction with anything, and hence be true. Hilbert's idea sounds crazy to me. He developed full Formalism later.
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12151
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If we replace 'I' in sentences about me, they are different beliefs and explanations of behaviour [Perry]
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Full Idea:
If I leave a trail of sugar, and realise 'that I am making a mess', ...when we replace the word 'I' with other designations of me, we no longer have an explanation of my behaviour, or an attribution of the same belief, so it is an 'essential indexical'.
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From:
John Perry (The Problem of the Essential Indexical [1979], 'Intro')
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A reaction:
[compressed] A famous observation of Perry's, which leads him to challenge traditional accounts of belief and of propositions. I don't think I see a problem, if we have a thoroughly non-linguistic account of essentially unambiguous propositions.
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12709
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Motion is not absolute, but consists in relation [Leibniz]
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Full Idea:
In reality motion is not something absolute, but consists in relation.
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From:
Gottfried Leibniz (On Motion [1677], A6.4.1968), quoted by Daniel Garber - Leibniz:Body,Substance,Monad 3
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A reaction:
It is often thought that motion being relative was invented by Einstein, but Leibniz wholeheartedly embraced 'Galilean relativity', and refused to even consider any absolute concept of motion. Acceleration is a bit trickier than velocity.
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15204
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Actual tensed sentences cannot be tenseless, because they can cite their own context [Perry, by Le Poidevin]
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Full Idea:
In the new tenseless theory, no tensed token sentence can be equivalent to a tenseless token, because the former, unlike the latter, draws attention to the context in which it is tokened.
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From:
report of John Perry (The Problem of the Essential Indexical [1979]) by Robin Le Poidevin - Past, Present and Future of Debate about Tense 3 a
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A reaction:
So the problem about indexicals was worrying fans of the tenseless B-series view of time (and so it should). I'm inclined to translate sentences containing indexicals into their actual propositions, which tend to avoid them. 'Time/person of utterance'.
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