[lit-ideas] more bar-p -q grub, anyone?
- From: "Henninge, Richard" <henninri@xxxxxxxxxxxx>
- To: "lit-ideas@xxxxxxxxxxxxx" <lit-ideas@xxxxxxxxxxxxx>
- Date: Wed, 6 Feb 2008 18:59:32 +0100
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
------------------------------------------------------------------
To change your Lit-Ideas settings (subscribe/unsub, vacation on/off,
digest on/off), visit www.andreas.com/faq-lit-ideas.html
Other related posts:
