Re: [ontolog-forum] Essences and modality

[Thomas Johnston <tmj44p@xxxxxxx>]

John,

I would indeed like to participate in a discussion of ontology and modal logic. It seems a logical (8>) next step from the discussion I started on ontology and predicate logic. I have some other stuff to get out of the way first, but I will read your article in the next week, and provide questions and comments as soon thereafter as I can. 

I expect that we will be discussing, among other things, Aristotle's essential vs. accidental change distinction, Kripke's position on analytic a posteriori statements, and Kripke & Putnam's position on the externalism/internalism debate. The issue of possible worlds and their accessibility is too obvious to mention.

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.

Tom

On Thursday, October 22, 2015 8:56 AM, John F Sowa <sowa@xxxxxxxxxxx> wrote:

Many discussions of ontology use words like 'essence' or 'essential'.
I don't like those words because they sweep a large number of
ontological commitments "under the rug".

Those words imply some kind of modality, which implies some
kind of modal logic, which brings in another host of implicit
commitments, which are often modeled by Kripke's possible
worlds, which people like David Lewis claim are "really real",
which "blows the minds" of people who believe that there is only
one world (or universe) that is really real.

For those reasons (and others), I prefer Dunn's semantics, which
is logically equivalent to Kripke's.  But it makes the ontological
commitments explicit, clearer, and more precise.

Michael Dunn showed that every Kripke-style accessibility relation
can be derived from a choice of "laws" that govern the possible worlds.
Each law is an explicit statement in FOL that states the commitment.

If you have a multi-modal logic, you can have as many laws as you
like to represent each of the commitments.  And you can even allow
different "worlds" or  "world-like models" to have different laws.

For more about worlds, modality, and laws with references to
Kripke, Dunn, et al., see http://www.jfsowa.com/pubs/worlds.pdf

John

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