Re: Philosophy general debate

Perhaps I was slightly ignoring what you were saying. Sorry, there are definitely implicit premises in arguments, probably there are implicit premises in ALL arguments. I think that this is called enthematic reasoning, but maybe I made this term up. It is an assumed premise that all trees are plants. You are correct to say that this truth is independent of the formal validity of the argument. All I was suggesting, to get back to philsophy and being sad, was that although by itself the argument to the effect that philosophy is saddening isn't incorrect ( i.e. that the conclusion is false), the argument is not by itself. Empirical and/or empirical investigation shows that all trees are plants, and similarly having a quick look will reveal philosophy that is not saddening. You are correct that this is an extra step, but it's an easy step to make, so let's make it.

On 24 Aug 2006 13:22:05 +0100, djf500@york.ac.uk <djf500@york.ac.uk> wrote:

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Hi,

By presupposition, all I mean is what must be in place before someone can
accept a starting proposition. I think that the form we are dealing here is
as with Moore's proof of the external world (and the fault is the same).
Here's a version of Moore's proof:

1)  If I have hands, then there is an external world.

2) Here is a hand [raises left hand], here is another hand[raises right] -
I have hands.

Therefore:

3)  There is an external world.

The fault with this appears to me (obviously I didn't think of this first!)
that in order to accept (2) we already have to be convinced of (3).
Although the argument is formally valid, it fails to be cogent because it
can't force us to believe anything new. The notion of presuppositions that
I have used helps to explain why this happens...

One does not - usually - have to claim explicitly that there is an external
world before we point at things and claim them to be present. However, it
is clear that if there is not an external world, then there are no hands.
So if someone denies that there is an external world, they cannot
reasonably accept that there are hands. Therefore, the claim that there are
hands cannot come to bear on the issue, because it (the issue) has to be
decided antecedently - even if it seems bloody obvious to *us*. I would
call the external world proposition (3) a presupposition of the hands
proposition (2).

I've seen this form presented as involving an implicit disjunction before
the explicit argument:

0)  Either there is an external world OR there is not an external world.

The contention (that I support) is that in order to move from (0) to (2),
we must already come down on the side of the affirmative disjunct, and so
choose (perhaps because of a really good argument) BEFORE WE START whether
to accept the proposed conclusion of the argument - we cannot be convinced
of anything NEW. That's a presupposition. (I'm sorry for the UPPER CASE,
but my email doesn't let me use italics - sometimes I use '*...*' and
sometimes capitals for emphasis - i'm not angry!). Accepting the premise
requires preacceptence of the conclusion, because of the implicit
presuppositions of the argument - that's why it can be called implicit
question-begging, but if that title annoys anybody the fact still seems to
remain that arguments of the form disussed are NOT COGENT and can ONLY
CONVINCE THE CONVERTED.

I think that Andrew (B) is with me on what I mean by 'presupposition'. But
the key word in his query is 'refute'. Of course if one refutes the
presuppositions of an argument then you've gone along way to refuting the
argument (though perhaps we might find a completely different set of
presuppositions to support the same explicit argument - I don't know) - but
what i'm saying is that an argument shouldn't try to prove it's own
presuppositions by smuggling them in with an innocent-looking premise. Of
course, i've explained the idea of a single presupposition and Andrew uses
the idea of the whole set - but I think that, for present purposes, we're
in tune.

I won't apply this to the tree example yet, perhaps it's obvious. Perhaps
people could say what they think about what i've said using Moore's proof.
With regard to calling the tree-sceptic a semantic-sceptic, all I meant to
refer to was his apparent doubt regarding the meaning of tree and plant
(assuming that what it is to be a tree involves being a plant, by virtue of
the ACTUAL meanings). That's another term I have no problem with dropping,
and of course how things have meaning is a whole new kettle of elephants.

Cheers,
Daniel

P.S. I've always been a bit confused as to how to use the word 'lemma'. By
my current understanding I might have used it to describe the proposition
that would affirm the left hand side of the disjunction above. I'd really
like to be told by someone who knows absolutely and for sure.

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