On 19 Jul 2016, at 06:58, Bruce Kellett wrote:

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.

But then computationalism is made false. With computationalism, or with Everett, the duplication illustrates the non transitivity of 1p identity. There is no problem with this, other than eventually justifying the physical laws by arithmetical self-reference. And this is confirmed by the fact that the logic of alternatives continuation in that frame gives exactly what we expect: a quantum logic.

Bruno






Bruce

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