On Mar 10, 2009, at 12:02 PM,
Sorry for the delayed reply, I have been otherwise engaged.
Ali Hashemi wrote: eep! Aside from the typos, i think the cl snippet i posted was actually a second order statement.
CL allows second-order syntax. I very much doubt that you need it to be semantically 2nd-order. Regardless however, any CL axioms would be along those lines.
Some other corrections, Gibson's work touches on the equivalence starting from section 6.3.2 (not 6.4), and his work can be found here:
This is a wonderful read, by the way, and a perfect illustration both of the joys and the frustrations of real philosophy. Additionally, the following paper by Varzi may clarify some additional question re the relationship between the two views: Varzi (2007) - Promiscuous Endurantism and Diachronic Vagueness - Ameri Philo Quart
And finally, in case people would object that this inter-translatability (indeed, quite explicitly, not ontological equivalence), would force one to countenance types of entities in their ontology that they would rather not, in the 3D view, importing 4D objects actually imports pairs of objects. Admittedly, this would restrict one's ability to quantify over the resultant entities.
I don't think one needs to use the pairs construction. For example, it could be treated as a function on times, and CL allows one to quantify over those.
Conversely, in the 4D view, importing 3D objects would amount to importing instantaneous slices of the object
No, it is worse than that. The 4d view (most of them) already allows 3-d temporal slices of a history. But a continuant isn't one of those, as it is the same - identically the very same - thing at different times, whereas any time-slice is of course not the same as a slice at a different time. The only way to allow continuants in a 4-d ontology is to not allow them to be spatiotemporal entities at all. (Except, possibly, elementary particles, or at any rate very small chunks of stuff which can be treated as atomic.) They are a kind of temporal abstraction which represents some set of cross-time "identity conditions", and which therefore define spatiotemporal extents, but they are conceptually distinct from those extents. So it is a category error to use spatial and temporal relations directly on continuants (again, in a 4-d ontology). Seen from the continuant (endurant) perspective, this simply confirms the fact that the so-called 4-d view amounts to nothing more than an insistence that every (physical) thing is an occurrent: it denies the physical reality of continuants. -- you never have to directly admit the existence of things you don't want in your ontology.
I guess, if there are no serious errors in this email and the last, are there any practical considerations which might hinder such interoperability (aside from the non-existence of axioms thus far)? Is the 3D-4D debate really an issue for people developing actual ontology applications?
It is, because there really are some tricky problems in making the various formal ontologies cooperate, and because both views have been used in actual deployed ontology standards. So we really do have an interoperability issue here. I don't say the situation is impossible, but it is of more than purely theoretical or philosophical interest.
Pat
Cheers,
Ali On Tue, Mar 10, 2009 at 12:11 PM, Ali Hashemi <ali.hashemi+ontolog@xxxxxxxxxxx> wrote: Hi all,
For those who are interested, check out: - Mark Hinchliff (1996), The Puzzle of Change. Philosophical Perspectives, 10, Metaphysics, 1996. pp. 119-136.
for a nice overview of the issues at hand here.
In - Trenton Merricks (1999) Persistence, Parts and Presentism, NOUS 33:3 (1999) 421-438
we get two nice definitions of the two accounts:
(1) For any presently existing object 0, 0 endures if and only if 0 persists
and all of O's parts simpliciter exist at the present time. I I
We can give a parallel account of what it is for an object to perdure:
(2) For any presently existing object 0, 0 perdures if and only if 0 persists
and some of O's parts simpliciter do not exist at the present time.
While in - Storrs McCall & EJ Lowe (2003). “3D/4D Equivalence, the Twins Paradox, and Absolute Time,” Analysis 63, pp. 114–23.
and - McCall & Lowe (2006). "The 3D/4D Controversy: A Storm in a Teacup." NOUS 40:3 (2006) 570–578
we get an argument for the equivalence of the two perspectives. They come closest to actually positing axioms showing equivalence:
The reader will have noticed that there is a close similarity between the set
of 3D particles which constitute an enduring object O at a time t, and the
instantaneous 4D temporal part of O at t. This fact provides for a simple
translation scheme between the 4D temporal parts ontology and the 3D
particle ontology. Let T(O, t) be the instantaneous 4D temporal part of O at t,
and let <O, t> be the instantaneous 3D sum of the particles which constitute
O at t. In 4D ontology, O is the mereological fusion of all its temporal parts
T(O, t), one for each moment at which O exists. In 3D ontology, O is the
set of particles which successively constitute it at each moment O exists, a
set which “changes”, i.e. is replaced by a new set, each time O gains a new
particle or loses an old one. To translate from the 4D to the 3D description
of O, reduce O to its temporal parts, and replace each temporal part T(O,
t) by the momentary sum <O, t> of particles which constitute O at t. The
collection of all such momentary sums <O, t>, for every time at which O
exists, yields the set of sets of 3D particles which successively constitute O.
Conversely, to translate from the 3D to the 4D description of O, first reduce
O to the momentary sums of particles which constitute it, then replace each
<O, t> by the corresponding temporal part T(O, t), then reconstruct O as
the fusion of its temporal parts.
I haven't been successful at finding people who disagree with McCall and Lowe's observations, the closest is in a phd thesis found here:
Gibson (2007) Time, Objects, and Identity - pihlisci archive, Oxford PhD (section 6.4).
He argues, (rightly imo) that their appeal to particles is unnecessary and potentially distracting. He also seems to assert that their position is of ontological equivalence, tho McCall and Lowe never explicitly state this. These two points aside, Gibson's major quibble arises from the equivalence between 4D-3D being based (implicitly) on linking X with "the life of X." Based on this, Gibson notes that the parts of one's life are not equivalent to X himself. I don't agree with this line of reasoning as it seems to me he is conflating several senses of life to derive this apparent oddity, the sense of life required for the mapping to work is exactly that which captures X and his properties as the parts of X's life. Whether this is too technical a definition to be palatable is another issue, which imo, doesn't affect engineering / business considerations. If it is so objectionable, let's call it not "life of X", but "X through his life."
Anyhow, I thought I'd post this to the forum and see what people have to say.
For the record, I don't believe that the 3D-4D translation provided in McCall and Lowe (2006) is ontological equivalence. Moreover, for someone developing ontologies for practical applications, i think logical equivalence suffices. Anyone disagree?
Finally, as many have pointed it, we haven't really come across any ontology which has formalized these notions of perdurance and endurance. I would imagine if one wanted to actually enforce a 4D view in an ontology, they'd need a second order axiom, otherwise, they could use CL's ability to quantify over explicit relations via an axiom similar too
whenever you have a relation (i.e. Rel1) you want to be restricted to the 4d view, you would state:
(forall (Rel1) (4DRel Rel1))
then you would have to have something akin to:
(forall (R ...) (if (4Drel R) (exists (t) (and (R ... t) (time t) (argument ...) ) )))
with appropriate axioms to define what an argument is. Though this style is coming perilously close to mixing meta concepts with the ontology itself.
Yet without a set of axioms, whether at the metaontology level or within the ontology, it is nigh impossible to develop a mapping through which one could prove, at least, logical equivalence between the two view points.
As Michael Gruninger pointed out though, there is high similarity between the notions of 3D-4D and time intervals and time points. While the latter are clearly not ontologically equivalent, their extensions may be mapped to logical equivalence over particular domains.
Cheers,
Ali
--
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