Combining Texts

Ideas for 'Writing the Book of the World', 'Set Theory and Its Philosophy' and 'Sophistical Refutations'

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2 ideas

5. Theory of Logic / H. Proof Systems / 3. Proof from Assumptions
Supposing axioms (rather than accepting them) give truths, but they are conditional [Potter]
     Full Idea: A 'supposition' axiomatic theory is as concerned with truth as a 'realist' one (with undefined terms), but the truths are conditional. Satisfying the axioms is satisfying the theorem. This is if-thenism, or implicationism, or eliminative structuralism.
     From: Michael Potter (Set Theory and Its Philosophy [2004], 01.1)
     A reaction: Aha! I had failed to make the connection between if-thenism and eliminative structuralism (of which I am rather fond). I think I am an if-thenist (not about all truth, but about provable truth).
5. Theory of Logic / H. Proof Systems / 4. Natural Deduction
'Tonk' is supposed to follow the elimination and introduction rules, but it can't be so interpreted [Sider]
     Full Idea: 'Tonk' is stipulated by Prior to stand for a meaning that obeys the elimination and introduction rules; but there simply is no such meaning; 'tonk' cannot be interpreted so as to obey the rules.
     From: Theodore Sider (Writing the Book of the World [2011], 06.5)
     A reaction: 'Tonk' thus seems to present a problem for so-called 'natural' deduction, if the natural deduction consists of nothing more than obey elimination and introduction rules.