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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12750
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The question is whether force is self-sufficient in bodies, and essential, or dependent on something [Lenfant]
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Full Idea:
The whole question is to know if the force to act in bodies is in matter something distinct and independent of everything else that one conceives there. Without that, this force cannot be its essence, and will remain the result of some primitive quality.
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From:
Jacques Lenfant (Letters to Leibniz [1693], 1693.11.07), quoted by Daniel Garber - Leibniz:Body,Substance,Monad 8
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A reaction:
This challenge to Leibniz highlights the drama of trying to simultaneously arrive at explanations of things, and to decide the nature of essence. Leibniz replied that force is primitive, because it is the 'principle' of behaviour and dispositions.
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