Re: An argument against modus ponens

On 8 Sep, 21:46, John Jones <jonescard...@xxxxxxx> wrote:
LudovicoVan wrote:
On 7 Sep, 02:57, John Jones <jonescard...@xxxxxxx> wrote:
LudovicoVan wrote:
On 6 Sep, 00:53, John Jones <jonescard...@xxxxxxx> wrote:
My post did not start and end this business. Things come together later.
For now, I am saying that 'if' statements are always informal and have
no place in a logic that looks after itself.
Ok, I can understand what you mean by the business is not over,
although there is a point that to me you keep missing (on purpose or
not, you know). See below.
OK.

'If' statements retain a variety of ontological and existential guises
and behaviours for the objects they present. These worldly contingencies
should have no place in a logic that delivers no more or less than it
presents.
The main problem is that no logic, formal or otherwise, is possible at
all unless grounded on the conventions of the natural language.
Yes. Understanding of course, that by "the conventions of the natural
language" you mean the matters dealt with language and not language per
se. If you mean the former, then I agree that your point is correct.

I would rather think it's the latter, although actually the two things
cannot be considered apart, as the point is indeed that language is a
matter of usage. The conventional nature of language is a grounding
notion in linguistics: it means that language (the natural language)
is a social construction that has to do with conventions and usage,
and there is no a priory. A very simple example might be: there is no
instrinsic reason why bread should be called "bread" and not -say-
"abadaf", and the same holds for grammar and syntax: there are rather
"historical" reasons (sorry, maybe better examples and discourse could
be provided, but my linguistics knowledge is now some 15 years old;
anyway this is in page 1 or so of any good introduction to
linguistics).

However, and bear this in mind - I was NOT arguing that logic is not
about convention or a posteriori events. BUT IF logic is about these
things, then logic must appeal to more than formalism and generalisation
if we want logic to present defensible scenario's (my example of modus
ponens is a case in point).

I agree on this. The emphasys on formalism is a mistake, for the very
reasons we are discussing here. (This does not really mean I get your
point with MP, but that's ok as far as you are using it as an example
to start a discussion.)

I'm in mind of Donald Davidson's comment that there is no such thing as
language. I find the notion of language as it is discussed in the halls
of philosophy deeply problematic. It has become an object among the
objects it presents.

Indeed, language reduced to communication. With that stuff one can
only build machines, which is not bad in itself, maybe the next
generation AI. I mean, not bad unless those machine are men.

It's like the One Cannot Not Communicate, and the very first
consequence is that silence is banned, and so all that really counts,
starting from mutual respect. Think cognitivism or psychological
functionalism of today. Think knowledge reduced to performative
skills. Think one-dimensional man. Think.

This holds for logical necessity, not just for contingencies: when we
say "if a man is a dwarf, than he is not tall", that's a logical
necessity, but we can say so just in so far as we know what the words
mean in the very first place.
I'm not sure about this. I would repeat my argument by first noting that
there can be no logical 'necessities';
  "If a man is a dwarf, than he is not tall" has no necessity about it.
The term 'then' tells us to look up a definition, and does not tell us
to look up a truth, at least in this example.

Yes, you have to "look up the definition", that is you have to know
what the words mean in the very first place. Then you are mistaken
about logical necessity, maybe because you are taking it too
informally: but that is not the case. The point on logical necessity
can go like this: once you know the meaning of the words, you can draw
so called incompatibility domains (sort of like Ven diagrams; I am
poorly translating back terminology from Italian books) to conclude
logical necessity or -conversely- logical incongruence between
predicates applied to the same subject, at the same time, in the same
place (in the same circumstances). Again, Strawson goes deep into what
incongruence and then necessity are in logic, chapter 1 to be
specific.

Otherwise, we must take logic as not a priori but a posteriori
In a sense, I'd say that's indeed it.
-LV
Ta, yes. Thinking about it...,
What could an 'insular' logic possibly be about?
And how could an insular system be 'created'?
Why, it's not possible.

If by "insular" you mean a logic that is self-sufficient, I'd say
nothing like that is possible. You can indeed have purly abstract
symbol games, still you have no "meaning" attached. Once you start
thinking about meaning (or application, etc.), then you are back to
natural language, as that's where any meaning comes from, explicitly
or implicitly that it be.

Anyway, I am near to handwaving here, so please take all this as hints
for further study, rather than anything too precise.

-LV

Well, handwaving is second only to semaphore, and that's got a foot in
both camps, formal and informal.

My semaphore is Red. Is that good or is that bad? ;)

-LV
.

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