Re: Fitch's paradox and OWA

From: Daryl McCullough <>
Date: 31 Dec 2009 20:26:16 -0800
Message-ID: <>

Marshall says...

>However what I was referring to was specifically
>how they get from step 7 to step 8 within that
>RAA proof. Your response does not seem to
>address that particular issue.

That's exactly the step that I was talking about. Steps (4), (5) and (6) and (7) constitute a proof of ~K(p &#8743; ~Kp). Therefore, we have |- ~K(p &#8743; ~Kp)

By C, if you have |- f, then you have |- [] f. Letting f = ~K(p &#8743; ~Kp), it follows that |- [] ~K(p &#8743; ~Kp)
which is step (8).

>Are your comfortable with how step 8 is
>obtained from step 7 via Rule C as described
>on this page?

Yes, that's exactly what they are doing. They didn't use the |- symbol in step 7, but it is clear that (7) is the conclusion of a proof.

Daryl McCullough
Ithaca, NY
Received on Fri Jan 01 2010 - 05:26:16 CET

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