Re: Fitch's paradox and OWA
Date: Thu, 31 Dec 2009 10:08:10 -0800 (PST)
On Dec 31, 7:10 am, stevendaryl3..._at_yahoo.com (Daryl McCullough)
> Jan Hidders says...
> >So what I wanted to say with the above is the following. You are of
> >course right that what (C) really says is:
> >(C) if |- f then |- f
> >And, assuming that for all f it holds that |- f iff ||- f, this is in
> >fact confirmed by the model theory. However, in the inference process
> >of the paradox as described on the Stanford page the rule is used as
> >if it says f |- f or |- f->f, and that would have the much
> >stronger model-theoretic meaning that I described.
> I don't see a rule saying f |- f. Where did you see that?
He didn't say that there was an explicitly stated rule of that form. He said that in step 8 of the derivation, they use a rule that was explicitly stated as
If |- f then |- f
but they use it *as if* the rule was
f |- f
Reading that page, it looks like what he is saying accurately describes the step taken, but I know very little about modal logic.
That's his point, as I understand it.
Marshall Received on Thu Dec 31 2009 - 19:08:10 CET