Sorry for the delay in replying. I am just back from a week’s
holiday in Morroco.
See responses below.
then featherless biped will include (from history) T. Rex,
mythology those creatures with a goats hind legs and a human torso and head.
My argument would be that for anything that is not provably equivalent,
is at least some possible thing in some possible world that is a member of
one but not a member of the other.
That seems to be the key. Your stance, then, is that
intensional differences will always be revealed as extensional differences in
some possible world: and if we agree to quantify panoptically over all entities
in all possible worlds, then it will be an extensional difference. Ergo,
intensional differences ARE extensional differences, if one casts ones
extensional net widely enough. Good point, though to be fair to the rest of the
philosophers, they are usually referring to extensions in the actual world
(maybe an eternalist one, but still without unicorns in it.)
[MW] Then they do not wish to be extensionalist. If you do, I
think you have little choice but to quantify over possible worlds (which is a
good thing, because it forces you down a single path and closes out many
What you say is very "natural" for someone with a background in logic
and traditional set theory which has a strong emphasis on
equating to sets or types, but this is not an inevitable
Of course, but that is the point. Extensionality *is* the
identify predicates with sets.
[MW] Perhaps I am not clear enough. My objection is having to accept
something set like whose membership can change with time. It may be my
error to conflate that with intensionality.
I think it is, yes. Personally I have no objection to
set-LIKE things which are dynamic: after all, everyday collections like flocks
of sheep seem to have this character. But my point was that to call these sets
is simply an error.
[MW] We have tried quite hard to eliminate anything that is not
a set. The one thing we have noticed that are set-like but not strict sets, are
what are often called ordered sets, e.g. the set of temperatures. The problem
here is that the same strict set may have more than one ordering.
There are a number of ontological positions that you need to
between, and it seems to me that we have not made all the
and this is what is resulting in the differences we have
The key choices that seem to me to be relevant here are:
1. Do particulars have temporal parts or not.
i.e. are particulars extended in time as well as space (or
Physical (spatiotemporal) particulars. The number 7 is a
but isn't spatiotemporal. Here's another way to say
it: can something
occupy space without occupying time? Yes (continuants) or no
[MW] Yes. At present ISO 15926 treats numbers as classes, and I appreciate
that is not the only, and may not be the best approach.
Hmm. I would prefer to treat numbers as numbers, myself.
[MW] Indeed, the question though is what sort of thing is a
number? You seem to be saying it is a particular, and in this way like a
spatio-temporal extent. I don’t see that similarity. For me the key
separation is between spatio-temporal extents and everything else, which I call
Abstract Object. Then sets, ordered sets and numbers would be subtypes of this.
However, I appreciate that there is an arbitrariness about the choices at this
level of abstraction. What is your rationale for making numbers particulars?
2. Extensionalism (or not) in particulars.
i.e. if particulars coincide, are they the same thing?
Do you mean spatiotemporally coincide? Like a bottle and the
is made of?
[MW] Yes, but the bottle and the glass it is made of will only coincide
accidentally. The usual case is that the temporal extent of the glass
is greater than the temporal extent of the bottle, and indeed the bottle
is a state of the glass. This also means that bottle is not a
subtype of glass-object (the whole of its life), but state-of-glass-object
Its not hard to imagine a scenario in which the thing and
the piece of stuff exactly coincide in 4-d. Consider for example a bottle made
of some heat-formed polymer, which is made by blowing a gas into a hot mold,
and comes into existence in the form of a bottle; and then ends its life by
being incinerated in a flash furnace. Here the bottle and the piece of stuff of
which it is made occupy the exact same 4-d history, but some folk would still
want to distinguish them. For example, someone might want to assert a property
of one but not the other. I agree its much less plausible to want to make the
distinction in cases like this, but I can see a pragmatic reason for doing so,
which is that we make the distinction in the more usual cases, perhaps for good
extensionalist reasons, so why should we be forced to not make it here?
[MW] This is just the price of extensionalism. Your only
alternative is to say that sometimes two different things occupy the same
spatio-temporal extension. Once you admit exceptions, the slope is very
slippery. As I say, I have yet to find a case where it actually mattered (and I
have been looking for them for many years now). I would be very interested in
any difficult examples you could produce that challenged that position.
3. Eternalism vs presentism.
i.e. is everything that exists what exists now, or is
exists include all that exists in the past and the future?
Also possibilism: even hypothetical things exist. But this
has to be taken with a pinch of salt, or at least clarified,
really doesn't mean what people ordinarily mean when they
the world in English. We say things like, "The hadron
didn't exist in the sixteenth century." I suggest
a better (less
confusing and contentious) way to say it is, the logic
possible, future and past entities in its universe: they all
*logically exist*. But only a small fraction of the things
*logically exist* ACTUALLY exist (i.e. in the actual world,
actual existence is a predicate (or a type, if you like) in
logical description. To 'logically exist' simply means that
it is a
thing that can be referred to, can be discussed, can be
given a name.
So this is really only another way to say that all names
is the basic semantic assumption of logic.
[MW] Well I'm nearly with you here. For me actually exist means everything
in our universe, for all time, and not restricted to now. That would be
a further restriction.
Speaking like an ontologist, I agree. But when you aren't
doing ontology, do you really talk this way? Would you say that Julius Caesar
exists, in the same sense that (unfortunately) Sarah Palin does?
[MW] I am quite happy to talk 3D as well as 4D. However, when I
want to integrate different views of the world, it is ALWAYS a 4D view that I
Now my choices are:
- Temporal Parts
- Extensionalism for particulars
- Extensionalism in sets
I agree except for the second. Don't you want to be able to
distinguish the bottle from the glass out of which it is
made? Or have
I misunderstood what you mean by this?
[MW] No you have not misunderstood, but I can distinguish between the
bottle and the glass (see above) and when I can't it does not matter,
because any statements I would make about it as one would also be true
of it as the other.
An intensionalist is going to say: but it may be true to say
of the bottle that it could have been made of polythene; but it is
nonsense to say that a piece of glass could have been made of polythene. I know
how you will get past this objection, but it illustrates that you have to be
careful when you say 'any statement'.
[MW] Of course, possible worlds again (it gives you a lot of mileage
once you have paid the price).
But this is philosophical debate, and IMO somewhat
irrelevant for Working Ontology :-)
[MW] Now here I completely disagree. I think that a rigorous and
well defined set of philosophical ontology commitments are critical to
practical working ontologies. If you do not make you commitments explicit, then
different workers on the ontology cannot be expected to conform to them, and
then you will have different commitments in different parts of your ontology.
Also, the more rigorous our ontology philosophically, the simpler it is
going to be, and that has processing implications as well.
I actually think that it is a great shame that philosophical
choices and their practical consequences are not discussed a great deal more in
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