Dear John, (01)
> Some comments on your comments from different, but related notes:
>
> JFS>> Making a clear distinction between actual sets and
> hypothetical
> >> or imaginary sets would be useful.
>
> MW> In ISO 15926 we used the term "class" for this. An overloaded
> > term I know. But I'd rather not start inventing new ones.
>
> I would recommend an adjective. Instead of using two different
> nouns,
> such as 'set' and 'class', it is much clearer to use one noun 'set'
> as the general term and add different adjectives to distinguish
> which kind of set you are talking about. (02)
MW: Yes, we did this in ISO 15926 - for example: class of individual.
There are some 10s of entity types that start class of ... (03)
MW: The names were not chosen for their technical correctness in
philosophical or logical terms, but for evoking the right idea in the
domain experts (engineers) who were to use the data model. So I think
there would have been little point in having an entity type called say
"trans world set" as a subtype of set.
>
> JFS>> But those sets [in possible worlds] are purely imaginary.
>
> MW> Lewis would disagree with you. He claims that are real
> > and not imaginary, hence modal realism.
>
> Lewis was using the term 'realism' in contrast with 'nominalism'.
> A strict nominalist, for example, would say that the so-called
> laws of nature are merely summaries of observations. But realists
> would say that any law that has been sufficiently tested, such as
> the Law of Gravity, is based on something real -- i.e., the law
> is an indication that there exists some *real* mechanism that is
> responsible for the observations. (04)
MW: That is not how I read Lewis. To me it seems quite clear that he
means that these possible worlds really exist, i.e. they are as real as
the world we inhabit, they are just inaccessible to us. Interestingly, I
heard a debate on the radio recently where some physicists were
proposing just the same thing.
>
> When people like Lewis say that there are such things as "real
> possibilities", they use examples such as the following:
>
> If I hold a pencil in my hand, I predict, with a degree of
> certainty that I would back with a wager of any amount you
> care to bet, that if I let go of the pencil, it will fall
> to the floor. (05)
MW: I don't think Lewis would have said anything like that. He would
have said that there is a possible world in which I let go of this
pencil and it falls to the floor. He would have considered that world
and any other possibility to really exist out there somewhere. He would
not even have used the language of contingency.
>
> Many people who are realists about physical laws would say that
> the possibility that the pencil would fall to the floor is real.
> In short, it is a "real possibility". I am willing to accept
> that terminology. (06)
MW: That is your choice. As I said, I am relatively indifferent as to
whether possible worlds really exist or not. Pragmatically, it does not
seem to make any difference to me, so it does not matter.
>
> However, saying that there are real possibilities does not imply
> that those possibilities are actualized. When I drop that pencil,
> the "mere possibility" becomes an actuality. Until then, its
> mode of existence is not the same as what non-philosophers would
> call "real". Despite my willingness to accept the term 'real
> possibility', I would still call an unactualized possibility
> "imaginary". (07)
MW: Again, this is not how a true possible worlds approach would see
things. Here all these possibilities are played out in some world, and
the only question is which of these possible worlds turns out to be
ours.
>
> If you prefer a different word, please suggest one. But it's
> important to recognize that real, but unactualized possibilities
> are not "really real" in the sense that ordinary people use. (08)
MW: It was Lewis's choice not mine, I can't unmake it for him.
>
> JFS>> Therefore, any use of set theory for representing physical
> >> entities must recognize that a set at one instant of time is
> not
> >> "exactly the same" set of supposedly "exactly the same" things
> >> at any other instant.
>
> MW> However, 4D neatly sidesteps this with states/stages/temporal
> > parts. The temporal part is unchanging and always a member of
> > the sets it is a member of. This is why 4D and set theory fit
> > well together.
>
> I'm sorry, but that is not a solution. Note that the person I
> quoted about the difference between the baby in the cradle and
> the grown man was Alfred North Whitehead. He had also developed
> one of the most detailed and elaborate 4D ontologies. In that
> quotation, he just happened to use a short illustration, but
> the point he was making is completely independent of 3D vs 4D
> ontologies. In fact, time is irrelevant to his argument. (09)
MW: Yes it is. Remember the objective is to be able to say anything that
is valid, but not necessarily in the way anyone wants to say it. So the
baby in the cradle is a temporal part of the whole life and the grown
man is a temporal part of the whole life. The temporal parts are
themselves members of babies in cradles and grown men. You know that
they are related because they are temporal parts of the same whole life.
Nothing here changes its set membership. What you are not allowed to do
is say that the persons whole life is at one time a member of babies in
cradles, and at another time a member of grown men. That is a
restriction of the approach - intentionally so.
>
<snip>
>
> I agree that a 4D view is conceptually cleaner than a 3D view
> for many of the theoretical discussions. But it's essential
> to note that the only direct knowledge we have is of the
> immediate present. The past is known only from memory or
> from records whose reliability has to be determined. And
> the future is totally unknown.
>
> When dealing with the real world, you can't do ontology
> without getting into all the problems of epistemology. (010)
MW: As Pat said, it is precisely the point of ontology not to get
sidetracked by epistemology. The fact that I have not seen every person
on the planet does not mean I have to question whether they exist.
>
> PH>> There are some cases that have been discussed in (at least)
> >> moral philosophy, involving identical twins, which at a very
> >> early stage of fetal development, in some cases, were one
> >> blastula. If life begins at conception, this is a difficulty.
>
> MW> What I like about 4D is that it allows this to be explained
> without
> > giving rules that forbid it as a matter of principle, but which
> also
> > does not make or force a choice about which twin, or either or
> > neither or both split from which. It just allows the situation
> to
> > be described.
>
> No. The entropy gradient defines a time arrow through a 4D extent
> that
> clearly identifies before and after. Theologians since Thomas
> Aquinas
> talked about 4D views, and they don't let you off the hook. (011)
MW: I have no problem with the arrow of time, but it has nothing to do
with the point I was making. I think you must have misinterpreted what I
was saying. (012)
Regards (013)
Matthew West
Information Junction
Tel: +44 560 302 3685
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http://www.informationjunction.co.uk/
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