Modal Logic

From: Eric Cavalcanti <eric.cavalcanti.domain.name.hidden>
Date: Thu, 11 Aug 2005 09:34:42 +1000

Hi Bruno,

On 8/11/05, Bruno Marchal <marchal.domain.name.hidden> wrote:

I am having a problem understanding this axiom:

> (...) Lob formula (B(Bp->p)->Bp), the main axiom of the modal logic
> of self-reference (G)
> can be interpreted as showing that some form of honest placebo effect
> works! But this is something I am still taking with some grain of salt.
> See the book "Forever Undecided" to see Smullyan exploiting the working
> of some self-fulfilling beliefs.

Suppose p = "it is raining today"

B(Bp->p) is true because I believe that if I believe it is raining today
it IS raining today, since If I believe it is raining today it is because
I have gone outside and seen that it is raining today, or I believe my
source of information for that matter.

But it doesn't follow from that that I do believe that it is raining today.
It happens by the way that I don't believe it is raining today, because
I can see a beutiful sun outside.

What's wrong?

Eric.
Received on Wed Aug 10 2005 - 19:36:37 PDT