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Re: [ontolog-forum] intangibles (was RE: Why most classifications are fu

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: sowa@xxxxxxxxxxx
Date: Tue, 19 Jul 2011 05:16:26 -0400 (EDT)
Message-id: <76cc2f9f2cd9a407542077c114b7a59a.squirrel@xxxxxxxxxxxxxxxxxxxx>

Dear Matthew,

It is true that talking about sets of possible worlds has the appearance of being extensional, but possible worlds are not observable.  They can only be specified by some intensional axioms or descriptions.

If you specify a set W of possible worlds by some set S of axioms, any results you get from analyzing W could be derived directly from S.  The seemingly extensional analysis is nothing but a round about way of using the axioms S to derive your conclusion.

In general, any set of possible worlds used for any version of modal logic (or any other kind of logic that uses Kripke semantics) can be replaced by some set of axioms (or laws) that generate exactly the same results without making any assumptions about possible worlds.

For further discussion of these issues, see



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