[lit-ideas] Re: more bar-p -q grub, anyone?
- From: wokshevs@xxxxxx
- To: lit-ideas@xxxxxxxxxxxxx, "Henninge, Richard" <henninri@xxxxxxxxxxxx>
- Date: Wed, 6 Feb 2008 15:47:43 -0330
Thanks to RH for his extended reply. However, I believe most of what he says
does not apply to anything I believe. Had he read the correction I issued in
response to RP's posting, he would have been apprised of the fact that I was
simply referring to modus ponens and modus tollens as the basis of Popper's
falsificationist criterion. (You gotta see this sentence in German!)
Most of the rest of RH's posting I find unintelligible. I hasten to add that I
am not a logician, so my view should not be deemed authoritive. But if RH is
himself a logician seriously pursuing the truth itself as his primary motive,
then his words below may well lay out an entire banquet of logical insight and
profundity.
Walter O
MUN
Quoting "Henninge, Richard" <henninri@xxxxxxxxxxxx>:
> Walter O wrote:
>
> I don't think we need to make a meal out of P[opper]'s views on
> falsification. Surely
> the essential points are two:
>
> 1. given (if p then q) and q, p may still be false.
>
> )) Can anything "given" be false? Aren't you creating a possible world in
> which "(if p then q)" and "q" are, qua givens, beyond truth and falsity?
>
> 2. given (ip then q) and not-q, it follows that not-q.
>
> )) This Robert Paul will find mysterious, that "given . . . not-q, it follows
> that not-q"; he will even reject it, saying, "Maybe in some possible world it
> does but not in this one," but then he turns around and says, so to speak,
> indeed, "[i]t does seem clear however that 'not-q' entails 'not-q' . . . ."
> Well, unless I am underestimating the power of single quotes, isn't he then
> both denying and affirming that not-q entails not-q, or otherwise formulated,
> that given not-q, it follows that not-q?
>
> )) Robert's first sentence raises some other interesting questions
> ("interesting" along the lines of "worth investigating in a 'philosophical
> investigation'--Wittgenstein's book title serving here as a sort of guard
> rail of scientificity or seriousness, about terrain beyond which one cannot,
> should not, ought not to speak). Does self-entailment not hold in all
> possible worlds? Robert says, ". . . but not in this one." Not in "this
> world" or in "this possible world." Is this world a possible world, or is it
> precisely, qua actual, not a possible world?
>
> Robert Paul responded:
>
> Walter mysteriously wrote
>
> > given (i[f] p then q) and not-q, it follows that not-q.
>
> Maybe in some possible world it does but not in this one. It does seem
> clear however that 'not-q' entails 'not-q,' one of the more notable
> advances in logic since Chrysippus.
>
> Robert Paul
>
>
> )) From beyond the Bay of Fundy Walter O invokes methylation among other
> causes for his lapsus, but then seems not to admit of a lapsus, and begins
> speculating about what "RP's point" actually was:
>
> I think I may have
> meant (don't hold me to it):
>
> given (if p then q) and not-q, it follows that not-p.
>
> )) So now it follows from not-q, not not-q, but not-p. Since Walter is not
> sure what he meant ("I think I may have meant . . ."), he tries instead to
> think of what Robert may have meant.
>
> RP's point, I think, is that, for example, given "If you get an A on the
> final
> exam then you get an A on the course" and "Erin did not get an A on the
> course," it does not follow that "Erin did not get an A on the course."
>
> )) I wish he hadn't said that. Now Walter is putting words into Robert's
> mouth that Robert would certainly find distasteful. In our logical shorthand,
> he believes, perhaps through isostatic rebound (if Greenland loses its ice
> topping the whole island will rise up out of/with the rising waters of the
> sea, thus recouping to some degree its submerging coast?), that "given (if p
> [you get an A on the final exam] then q [you get an A on the course]) and
> not-q [Erin did not get an A on the course], it does not follow that not-*q*
> [!!?? Erin did not get an A on the course]. No-no, that's not what Robert
> Paul was getting at; that's off the radar screen in terms of
> considerationability (sic). What happened (I hope) was that Robert was
> challenging what Walter O will subsequently say:
>
>
> (Some
> of our more German members may wish to inquire into the reason behind this
> oddity.)
>
> However - and now I'm extrapolating from RP's point to another point I
> believe
> he wishes to make and for which he begs our assent - it does follow
> inexorably,
> given the above 2 premises, that Erin did not get an A on the final exam.
>
> )) It is this so-called inexorability I think and hope Professor Paul is
> questioning: he has tacitly corrected Walter O's original
>
> > given (i[f] p then q) and not-q, it follows that not-q.
>
> )) to obtain a
>
> > given (if p then q) and not-q, it follows that not-*p*
>
> )) which he then dismissed with the comment, "Maybe in some possible world it
> does but not in this one," namely, it does not follow from Erin's having not
> gotten an A on the course that she had not gotten an A on the final exam. To
> be sure, p entails q, but q can be entailed by other circumstances. To
> satisfy Robert, Walter need only add an "f" to his "if"--"iff": given (iff
> [if and only if] p then q) and not-q, it follows that not-p. Now p is the
> necessary and sufficient condition for q, and not just a sufficient condition
> for q. Only under these conditions can bar-p be inferred from bar-q.
>
>
> And
> that's really all Sir Karl ever wrote about Erin.
>
> Interestingly, these questions of validity may be fully answered independent
> of
> any views provided us by Erin herself.
>
> )) Shouldn't that be "information" and not "views," or is scenic Newfoundland
> isostatically rebounding sober information into breathtaking views?
>
> Walter O
>
>
> Richard Henninge
> University of Mainz
>
>
>
>
>
>
>
>
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