It looks to me that Russell was pretty much making the same point that I was
making. The lesson is not to confuse a rule of inference (Russell's "p,
therefore q") with another premise (or proposition) to be justified
(including propositions like "p implies q"). If all you had were
propositions and no rules of inference, you'd never be able to get anywhere.
No amount of mere propositions strictly by themselves will justify
deduction.

The more general lesson is that it's a mistake to think you must answer the
skeptic on his own terms. (It usually seems to be a he.)

Ku

http://www.umich.edu/~jsku


On 3/2/07, gts <[EMAIL PROTECTED]> wrote:

On Fri, 02 Mar 2007 03:25:58 -0500, John Ku <[EMAIL PROTECTED]> wrote:

> Skeptics are fond of pointing out that no non-circular argument can be
> given to support inductive reasoning. That is true, but a century ago,
> Lewis Carroll showed through his modern parable of Achilles and the
> Tortoise that the same holds as well for deductive reasoning.

Is that really true? What do you think of Bertrand Russell's answer to
Carroll?

Russell argued that Carroll failed to distinguish between asserted and
unasserted propositions. The statement "if p then q" is not at all the
same as "p, therefore q". The Tortoise in Carroll's story failed to make
this important distinction, confounding poor Achilles.

The Principles of Mathematics by Bertrand Russell
http://fair-use.org/bertrand-russell/the-principles-of-mathematics/s.38

-gts

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