Re: Contexts and quantifiers in KIF

Jim Fulton <jfulton@atc.boeing.com>
Date: Tue, 13 Apr 93 10:09:04 -0700
From: Jim Fulton <jfulton@atc.boeing.com>
Message-id: <9304131709.AA13792@atc.boeing.com>
To: cg@cs.umn.edu, sowa@turing.pacss.binghamton.edu
Subject: Re: Contexts and quantifiers in KIF
Cc: interlingua@ISI.EDU, jfulton@atc.boeing.com, srkb@ISI.EDU

John,

This is a comment on your reply to Chris's comment.

I guess I am more of a realist about possible worlds (by whatever name).  I 
certainly do not regard them as mere data structures, rather they are what 
"could" be represented by those data structures.  

The "could" in that assertion on the interpretation of the modality used in 
those data structures, or equivalently (as Kripke showed) on the interpretation 
of the accessibility relationship among the worlds.  Some examples:

1.  I use the words 'not' and 'and' in such a way that for any sentence P 
it is logically false that P and not P.  That means that there is no possible 
world in which a sentence is both true and false.  This modality, i.e., 
logical truth and falsity, is rather easy to write off as saying something 
about words and not about worlds.  It represents decisions about our choices 
for using language in ways we regard as consistent.

2.  The sentence 'Bush was President' is true now in virtue of the fact that 
the sentence 'Bush is President' was true previously, i.e., in virtue of the 
fact that there was a time (we refer to "times" in normal English, but what 
we seem to be talking about when we do so seems more like a world) at which 
the person, here referred to as 'Bush', had the office, here described as 
'is President'.  Under the temporal interpretation of modalities, possible 
worlds are no more mysterious than history or the future.  They are not data 
structures; they are the past or future states of the world.  

3.  There is a significant sense in which the following sentence is true:
'Bush could have been re-elected, although he was not.'  Here the 'could' 
reflects not a logical possibility but a "causal" or "historical" one.  
Much of our ability to learn from the past involves our understanding of 
what would have happened instead if ....  Perhaps the most interesting use 
of modal data structures is to describe precisely the causal consequences of 
of roads not taken (what are all the differences that makes?).  The possible 
worlds here are REAL to the extent that the modal statements (i.e., it COULD 
have been ...) are TRUE.

So before we write off possible worlds as mere data structures, let's look 
a little more closely at the reality represented by the true sentences in 
those data structures.

Jim