Ben Bacarisse <
ben.u...@bsb.me.uk> writes:
> "Chris M. Thomasson" <
chris.m.t...@gmail.com> writes:
>
>> On 10/5/2022 7:24 PM, Fritz Feldhase wrote:
>>> On Thursday, October 6, 2022 at 3:57:16 AM UTC+2, Chris M. Thomasson wrote:
>>>> On 10/5/2022 1:12 PM, Dan Christensen wrote:
>>>>>
>>>>> The Drinker’s Theorem: Consider the set of all drinkers in the
>>>>> world, and the set of all people in a given pub. Then there
>>>>> exists a person who, if he or she is drinking, then everyone in
>>>>> that pub is drinking.
...
> But, as is so often the case, Dan misses a chance to explain. This is
> only a paradox of ambiguous language. The English wording contains two
> elements of misdirection. Both the "if ... then ..." and the "there
> exists ... such that" suggest causality which is not there in the logic.
>
> If we replace the implication with a disjunction, thing are much
> clearer: There is a person (in the pub) such that either (a) they are
> not drinking, or (b) everyone is drinking. But even now the "such that
> everyone is drinking" sounds as if this state of affairs might be being
> "caused".
>
> To avoid this the "there exists x such that..." is more clearly
> expressed as choice: in any non-empty pub, we can find someone who is
> either not drinking or is drinking with everyone else.
From a language perspective, I'd say that these are still worded so that
they are false. The "is drinking" is a continuing action, and the "is"
implies constancy, thus continuing to be true while the "is drinking"
applies. The is_drinking predicate D() is not constant, it's varying
over time - and the drinker, likewise, needs to be able to vary over
time. So there doesn't "exist *a* drinker", as that implies constancy,
which is inappropriate.
The paradox is is worded more like:
exists i in P : forall t D(i,t) -> (forall j in P D(j,t))
but the logical explanation is explaining this:
forall t exists i(t) in P : D(i(t),t) -> (forall j in P D(j,t))
That's not even a swap of the quantifiers, that's a more significant
change.
Word things badly, in ways that overlook how language is interpreted,
and you'll get contradictory conclusions. Them's the breaks.
Phil
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