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Re: [ontolog-forum] Universal and categories in BFO & DOLCE

To: "'[ontolog-forum] '" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Matthew West" <dr.matthew.west@xxxxxxxxx>
Date: Mon, 5 Sep 2011 07:41:42 +0100
Message-id: <4e646f28.d1c7e30a.58de.51cc@xxxxxxxxxxxxx>
Dear John,    (01)

> As we've discussed before, I agree that sets are involved --
> as they are in the model theory for any logic.
> 
> > MW: Also 4D ontologies that use possible worlds can define
> > classes as sets, as has been discussed on this list in the past.
> 
> Yes.  But when you talk about sets in possible worlds or sets
> in 4D regions that are inaccessible because they are outside
> the time cone of observability, you can't get any information
> from them -- except for whatever assumptions you put into
> the definitions of those worlds.    (02)

MW: You can also postulate facts that will be true in a particular possible
world. I would consider it disingenuous to construe those as definitions of
the world. This principle is central to the way that possible worlds are
used in practice for e.g. planning.
> 
> > MW: A problem with defining classes as sets for ontologies with other
> > foundations is that you cannot talk about imaginary things like
unicorns,
> > because they all equate to the null set, and other definitions might
> > accidentally give identical sets, even though they are not necessarily
> > identical.
> 
> I agree.
> 
> But I would add that you can have possible worlds with non-null sets
> of unicorns.      (03)

MW: Of course. That is why the use of possible worlds permits you a system
that does not depend on types.    (04)

> However, any data you get about unicorns in those worlds
> are just implications of your starting assumptions about them.    (05)

MW: No they are not. They can also be facts that you stipulate to be the
case in that particular possible world. Facts are not assumptions.    (06)

Regards    (07)

Matthew West                            
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http://www.matthew-west.org.uk/    (08)

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> 
> John
> 
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