To infer means there is "a process" which permits to infer.. if there
is none... then you can't simply infer something.
2008/11/9 Brent Meeker <meekerdb.domain.name.hidden>:
>
> Quentin Anciaux wrote:
>> 2008/11/9 Brent Meeker <meekerdb.domain.name.hidden>:
>>> A. Wolf wrote:
>>>>> I can if there's no rule of inference. Perhaps that's crux. You are requiring
>>>>> that a "mathematical structure" be a set of axioms *plus* the usual rules of
>>>>> inference for "and", "or", "every", "any",...and maybe the axiom of choice too.
>>>> Rules of inference can be derived from the axioms...it sounds circular
>>>> but in ZFC all you need are nine axioms and two undefinables (which
>>>> are set, and the binary relation of membership). You write the axioms
>>>> using the language of predicate calculus, but that's just a
>>>> convenience to be able to refer to them.
>>>>
>>>>> Well not entirely by itself - one still needs the rules of inference to get to
>>>>> Russell's paradox.
>>>> Not true! The paradox arises from the axioms alone (and it isn't a
>>>> true paradox, either, in that it doesn't cause a contradiction among
>>>> the axioms...it simply reveals that certain sets do not exist). The
>>>> set of all sets cannot exist because it would contradict the Axiom of
>>>> Extensionality, which says that each set is determined by its elements
>>>> (something can't both be in a set and not in the same set, in other
>>>> words).
>>> I thought you were citing it as an example of a contradiction - but we digress.
>>>
>>> What is your objection to the existence of list-universes? Are they not
>>> internally consistent "mathematical" structures? Are you claiming that whatever
>>> the list is, rules of inference can be derived (using what process?) and thence
>>> they will be found to be inconsistent?
>>>
>>> Brent
>>
>> Well I reverse the question... Do you think you can still be
>> consistent without being consistent ?
>>
>> If there is no rules of inference or in other words, no rules that
>> ties states... How do you define consistency ?
>
> A set of propositions is consistent if it is impossible to infer contradiction.
>
> Brent
>
> >
>
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Received on Sat Nov 08 2008 - 20:41:21 PST