Re: [ontolog-forum] Essences and modality

[Thomas Johnston <tmj44p@xxxxxxx>]

John,

I think much the same thing about possible worlds. I think a Dr. Seuss story is a possible world, as is Dicken's Bleak House, as is any variation on this wonderful/terrible actual world of ours that anyone of us can imagine. This is unfortunate in the sense that it means that I may not be able to take enough of a confrontational position to stimulate a good discussion. Perhaps others can/will take up that responsibility.

But I don't know enough about accessibility relational among S1 - S5 possible worlds, and I would like to learn a bit more before I dismiss Kripke.

Tom

On Thursday, October 22, 2015 10:33 PM, John F Sowa <sowa@xxxxxxxxxxx> wrote:

On 10/22/2015 9:14 PM, Thomas Johnston wrote:
> If you regard all that as straying too far afield from what you
> conceive of as the scope of this topic you've started, let me know.

The claim I'm making is that underlying every version of modality
is some law or law-like principle that determines the distinction
between what is necessary (alethic), obligatory (deontic), or
known (epistemic) vs. what is possible, permissible, or believed.

My claim about possible worlds is that they're just a colorful
metaphor that has no explanatory power.  Kripke semantics requires
a primitive accessibility relation:  there is no deeper reason why
one world w2 is accessible from some other world w1.

Dunn's semantics replaces each world w by the set of all facts
(propositions) that are true of w.  And for each world w, there is
a set of laws that determine the accessibility relation:  w2 is
accessible from w1 iff every law in w1 remains true in w2 (but
some laws in w1 may be demoted to ordinary facts in w2).

From any Kripke model, you can derive an equivalent Dunn model
and vice versa.  But the advantage of Dunn's semantics is that
you can analyze the laws and give a deeper explanation of why
w2 is accessible from w1.

I also claim that *every* puzzle that can be solved by K's worlds
has an equivalent or *better* solution in terms of D's laws.

John

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