Re: logical matters

[ucleaar <ucleaar@UCL.AC.UK>]

Date:         Sat, 25 Nov 1995 18:25:57 -0800
From: "John E. Clifford" <pcliffje@CRL.COM>
> And:
> [I]t turns out that pc thinks A does entail E, while everyone else
> (this includes a lot of people) thinks it doesn't.
> pc:
> Open challenge.  Find me a logician (or even a mathematician who
> knows a bit of logic) who thinks that AxFx does not entail ExFx in
> the ordinary system (that is, one not doing free logic at the time he
> says it.

I am willing to concede defeat.

> Now, it is true that in the jargon of mathematics and logic, "All Fs
> are Gs" need not imply "Some Fs are Gs" [...]. But that is because
> "everybody knows" (since 1858 at least) that "All Fs are Gs" is --
> in the jargon - - short for "for every x, if Fx then Gx" and the
> conditional is material, true if the antecedent is false, as it
> will be universally when ther are no Fs.  Rather like Spanish, the
> trick is not in the quantifier at all, but, in this case, in the
> connective in the scope (BTW, anyone know a good Spanish logic book?).

Okay. So {ro da broda} entails {da broda}. But all other uses of {ro}
don't entail existence - {ro da poi kea broda cu brode} and
{ro broda cu brode} entail neither {da broda} nor {da brode}.

One ought to be encouraged, I think, to not use poi clauses with da,
and to instead use logical connectives.

coo, mie And