Thread View: sci.logic
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Started by David Gudeman
Sat, 07 Nov 1992 03:48
Re: Impredicativity - was: Russell's Paradox
Author: David Gudeman
Date: Sat, 07 Nov 1992 03:48
Date: Sat, 07 Nov 1992 03:48
37 lines
2144 bytes
2144 bytes
We better be careful or we're going to end up agreeing on more than just the inadequacy of ZF. In article <1992Nov6.193134.17283@guinness.idbsu.edu> Randall Holmes writes: ]Re Gudeman: ] ]Your criterion for an acceptable property is wrong. ] ]... Some perfectly well-defined open sentences which ]have truth values no matter what is substituted into them cannot have ]extensions or intensions. OK, you have a point. The open sentence "__ is not true of itself" does not form a proposition if you replace the blanks with something that stands for the sentence's (non-existent) proposition, but then you can't expect _any_ open sentence to form a proposition if you fill its blanks with non-existent things. I'll have to rethink my criterion, but that really does not affect my main point about recursion. ]Once again, there is no problem with ]self-membership or non-self-membership holding of particular objects; ]there simply is no "object" which is the extension of ]"self-membership" or "non-self-membership". And this does not mean ]that the objects in the universe are not unambiguously divided between ]the self-members and the non-self-members; there is no ambiguity, no ]gray area between them. But there cannot be a set of the ]non-self-members. I think we agree that there is no property (read "nonspatio-temporal mathematical object") associated with the set of open sentences of the form "__ is an element of __". Our difference is that you think there is a metaphysical explanation for this fact, and I think it can be explained entirely in terms of incorrect use of language. -- David Gudeman gudeman@cs.arizona.edu
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