On 19/07/2016 2:18 am, Bruno Marchal wrote:
On 18 Jul 2016, at 03:54, Bruce Kellett wrote:
As you say in another post, computationalism depends on the breakdown
of transitivity for personal identity: M is the same as H; W is the
same as H; but M is not the same as W. Given this, you have all sorts
of problems with the nature of personal identity -- maybe it is not a
modal concept! I will talk more about this in reply to your other post.
Well, the machine notion of 3p-self can be defined in arithmetic, and
all correct machine knows that her 1p-self is not. Sure it is a tricky
notion, but the non transitivity is not a problem, as the "Parfit
person series" will work transitively in all cases, except when
duplication occurs, but why would that cause any problem, you tell me.
Nothing here threats the validity of the reasoning leading to the
reversal physics/arithmetic. I think you confused non transitivity
(the failing of some transitive link) with intransitivity (the failing
of all transitive link). With self-duplication, we lost transitivity
in one case, but both surviver recover it as long as they do'nt
duplicate again, and so the old guy who stayed in Moscow remains the
same young guy who teleported at Moscow through some duplication a
long time ago. You might elaborate on your problem, as I don't see any.
I think a relation is either transitive or it is intransitive: personal
identity is a transitive relation; 'father of' is an intransitive
relation. You can't be 'half-pregnant', as it were.
I quote from Wikipedia on personal identity:
"Generally, personal identity is the unique numerical identity of a
person in the course of time. That is, the necessary and sufficient
conditions under which a person at one time and a person at another time
can be said to be the same person, persisting through time."
And from the Internet Encyclopedia of Philosophy: www.iep.utm.edu/person-i/
"Personal identity is an instance of the relation of numerical identity;
investigations into the nature of the former, therefore, must respect
the formal properties that govern the latter. The concept of identity is
uniquely defined by (a) the logical laws of congruence: if X is
identical with Y, then all non-relational properties borne by X are
borne by Y, or formally "A(x,y)[(x = y) --> (Fx = Fy)]; and (b)
reflexivity: every X is identical with itself, or formally "Ax(x = x).
(Note that congruence and reflexivity entail that identity is symmetric,
"A(x,y)[(x = y) --> (y = x)], and transitive, "A(x,y,z)[((x = y) & (y =
z)) --> (x = z)]."
And later in the same article:
"Should fission be an acceptable scenario, it presents problems for the
psychological approach in particular. The fission outcomes Y1 and Y2 are
both psychologically continuous with X. According to the psychological
approach, therefore, they are both identical with X. By congruence,
however, they are not identical with each other: Y1 and Y2 share many
properties, but even at the very time the fission operation is completed
differ with regard to others, such as spatio-temporal location.
Consequently fission cases seem to show that the psychological approach
entails that a thing could be identical with two non-identical things,
which of course violates the transitivity of identity."
Fission, in this case, is equivalent to the duplication protocols under
consideration in this discussion. There does not seem to be any widely
agreed resolution of the problems that the duplication scenarios entail.
Some acknowledge that these scenarios indicate that psychological
continuity is not sufficient for person identity. "These commentators
typically complement their psychological theory with a non-branching
proviso and/or a closest continuer clause. The former states that even
though X would survive as Y1 or Y2 if the other did not exist, given
that the other does exist, X ceases to exist." This might be
problematic, however, and we could avoid some problems by adding a
closest-continuer or best candidate clause, stating roughly that the
best candidate for survival in a duplication scenario, that is, the
duplicate which bears the most or the most important resemblances to the
original person X, is identical with X." For instance, if the original
survives the duplication, he is the closest continuer and hence uniquely
identical to the original.
And so on. As I have said, the philosophical literature on personal
identity is extensive and quite complex. The idea of transitivity of
personal identity does seem to be central, so duplication cases are
often problematic.
Parfit's analysis seems to suggest that the duplication scenarios, since
they violate transitivity, entail that the original that is being
duplicated does not survive the duplication. However, in the duplication
case with two copies, Y1 and Y2, although the original X dies, having
two survivors identical to the original is even better that being
identical to just one survivor. "Generally, according to Parfit,
psychological continuity with any reliable cause matters in survival,
and since personal identity does not consist merely in psychological
continuity with any reliable cause, personal identity is not what
matters in survival."
Whatever line one takes with respect to personal identity in general,
and in duplication cases in particular, it seems clear that the simple
psychological account of personal identity is insufficient to survive
all the difficulties. Abandoning the transitivity of identity is
difficult in general because it is precisely that transitivity that
gives us a reliable notion of the continuity of personhood through time.
The things that might seem to violate transitivity in duplication
(copies in separate locations, etc, that is, non-psychological
differences), also would give violations of transitivity relating copies
of the same person at different times and places. We need a principled
account of exactly what leads to the violation of transitivity in one
case and not in the other. That is why I still think that the original
is the continuation if not deleted during duplication, and the duplicate
in that case is simply a new separate person -- sharing some background
and memories with the original, for sure, but actually a different
person. Identical twins can share many memories and other
characteristics without us ever thinking that they are two copies of the
same person. If the original is deleted during duplication, then two new
distinct individuals are created.
In this way, the important principles of identity, such as congruence
and transitivity, are respected in all cases.
Bruce
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