Identity across possible worlds does have some similarity with diachronic
identity, but not much. (01)
For diachronic identity, there is a reasonable intuitive understanding that,
for most of the mass of "the same" physical object, there will be a continuous
path in space-time which that mass traverses. even though some parts of it may
diverge. There is also a more conventional way of defining "identity" as in the
example provided by Fritz Lehman, where the army defines a "rifle" by its stock
serial number. In that case, more than half the mass may change while the item
retains its (conventional) identity. (02)
But for possible worlds, there is **no** continuous path to traverse, the
worlds are discontinuous; so to use the term "identity" may cause serious
misunderstanding and logical contradiction. As suggested by the referenced
article on "transworld identity"
(http://plato.stanford.edu/entries/identity-transworld/ ... for which,
thanks!), a 'counterpart' relation rather than identity relation would be less
prone to misunderstanding. (03)
For the case where there is a multiverse which forks for every collapse of some
entangled quantum system, there would be a different relation. The
'counterpart' entities in different universes could be traced back to the same
entity in an earlier universe, though their properties may diverge
dramatically. This would again be a different relation from 'diachronic
identity' or 'counterpart' (e.g. for fictional or hypothetical worlds) (04)
The point (for me) is to avoid logical contradiction, and the use of an
unqualified 'identity' or 'same' relation risks misunderstanding. Diachronic
identity is intuitively understood and relatively innocuous. But for possible
worlds, I would avoid 'identity' completely. (05)
>----- ------- Original Message ------- -----
>Sent: Wed, 11 Jul 2012 15:32:14
>On Tue, July 10, 2012 22:02, Chris Menzel wrote:
>> On Tue, Jul 10, 2012 at 5:25 PM,
>>> Wandering far off topic, ergo changing the topic
>>> A comment on the comment of Doug F.:
>>> >> However, one would stretch to come up with
>>> >> "an instance of the planet Venus" would be.
>>> This touches on an ontological issue that
>concerns me for several
>>> reasons: possible worlds.
>I'm not sure how this relates to the treatment of
>Venus as a class.
>Do you mean the class of all possible planets
>>> Consider the planet Venus in each of the Sci-Fi
>novels in which the
>>> planet is described - it can have different
>>> therefore is in fact a different individual.
>> That is *far* from clear. Suppose in one story it
>simply lacks a single
>> grain of sand that it actually has. I'm certainly
>not inclined to say it
>> is a different individual.
>It depends upon the definition of the individual.
>Just like Theseus's ship.
>Is Venus the same individual today that it was last
>year? It has different
>mass, grains of interstellar dust that it didn't
>have then, and has lost
>hydrogen from its atmosphere.
>The Venus in any Sci-Fi novel is far more similar
>in properties to the Venus
>that recently transited the Sun than my current
>properties are to those
>of the Doug Foxvog of 50 years ago. If that is the
>basis for determining
>whether something is a different individual, i and
>Foxvog are certainly two different individuals.
>-- doug foxvog
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