Parfit’s reductionism of personal identity comes into picture as a radical solution to the duplication problem (assuming that we accept the psychological continuity theory), wherein a personal identity in terms of its psychological continuity could branch into two (or more) successors, each of which is continuous of the previous personal identity before branching and is hence identical to each other, thereby we would seem to have two (or more) persons (or agents) having one and the same identity, thus violating the rule of numerical sameness upon which we build our previous accounts of personal identity. Instead of simply adding the clause such as “this psychological continuity does not take a branching form” as a way to tackle this duplication problem, Parfit has otherwise suggested his reductionism view. This account entails two major arguments, as that 1) the thing as we call “personal identity” is indeterminate and consequently we should see how 2) (the issue of) personal identity might not be as important as it seems to be. These two arguments would be in order discussed to explain his argument for reductionism. First, to say that the personal identity is indeterminate is to say that personal identity is not numerical identity, implying that every bit of changes of the either person’s material constitution (in terms of the spatiotemporal continuity) or of his psychological states (in terms of the psychological continuity) does change the person into a different one; this is the strongest case where we seem to never be the same person the next second (every time you breathe you become different!). More specifically, this indeterminacy could be understood by considering personal identity as a spectrum rather than a true-false conditional, one end of which is the exact same person with everything intact, starting from where we continuously “change” a little bit of the person, say, erasing his apparent memories (the case of the psychological spectrum), replacing his body and brain cells with exact duplicates (the case of the physical spectrum), or replacing his body and brain cells with NOT exact duplicates (the case of the combined spectrum), until there is nothing left with which we could identify the changed as the previous person, where is the other end of the spectrum. At first, we could be very confident in identifying the changed person as the intact one (i.e., who is only replaced 1% off his body or brain cells or only a few apparent memories are erased); however, while the process keeps going, we become less confident in the identification, and it therefore seems we are urged to say that the person (or his identity) has ceased to exist or survive at some point along the spectrum. It is especially so in the case of the combined spectrum where the person becomes both less physical and psychological when waking up (Bear with me that I do not address the three spectra individually in an effort of carrying out the point more succinctly).
Moreover, if we decide that the person should survive case n, by the same logic we should also decide that he survive case n+1, n+2, n+3… in seeing personal identity as transitive. However, it is clear, at least intuitively, that the person should cease to survive at some point, at least it is the case when there is nothing left of him at the other end of the spectrum, implying that the person would survive at the one of the cases but somehow die at the next, which is certainly counterintuitive and not of common sense. Therefore consequently, we should either accept 1) there is a certain distinct cut-off after which the person cease to survive, or 2) the person survives all the time even though he is by definition completely and distinctively different at the end from who he was before in terms of his physical constitution or of his psychological states; or, as Parfit strongly suggests, 3) there are “borderline cases” where the question gets so vague that we just cannot answer it and thus the personal identity is in this sense indeterminate. It is obviously that to accept 1) would be irrational, and since we seem to be unable to distinguish with certainty the distinct cut-off in 2), account 3) wins out as the most constructive solution in this context.
However, once we accept the account 3), or even accept account 2) without the ability of finding the cut-off, which seems an impossible mission, the issue of personal identity does not matter any more; it does not matter whether I would be the same person next second, insofar as I regard the significance of me having the same personal identity, i.e., what it entails rather than what it is. It just (in part) because we regard that personal identity significantly carries on our beliefs, desires and other mental states that we regard the issue of personal identity. Therefore, the issue of the continuity of personal identity is in this sense reduced into the issue of the continuity of psychological states that are connected with the formal, and thus what matters is the latter. And if personal identity does not matter, neither does death; I should even be pleased and relieved to have known that two persons would continuously love my children as I do after my death in case of the duplication problem.
Nonetheless, if we insist on the ontological question of personal identity per se, this reductionism seems only to get things more complicated, if not distressing. Since a materialism view of personal identity seems incapable for our purpose so far, an alternative dualism account advocated by Swinburne may provide some implications. A classical dualism view, especially according to Descartes, is essentially saying that we as persons are more than bodily matter, and it is this extra saucy something, or the immaterial soul-stuff, that is organized as a soul which defines the personal identity (the significance and the possibility of the soul-stuff being divisible seems to me not fully explained in the article). And this soul just is (or at least an essential part of) the personal identity. Therefore, it is the continuity of the soul that marks the continuity and the survival of a person. Thus, a person is said to be alive as long as he has the very soul as he is, despite that he may have a totally new body, or have no material body at all. More specifically, it is the consciousness in virtue of having the soul that matters to the personal identity at all; if I lost all my past memories and had a new body, it is logically possible that I could still consciously experience and interact with the world I live in. By the same logic, since the soul is who I really am, it is also possible that I am disembodied but still conscious. This is in correspondence with what Swinburne called simple view of personal identity as a response to Parfit’s account, which claims that though personal identity is closed connected to the spatiotemporal continuity of the body and the psychological continuity of the mental, these are only evidences or phenomena by and through which we think of personal identity and therefore essentially not personal identity, just as a finger print nay suggest the presence of a person but it is never the person per se.; or according to Aristotle, they are not essential properties of personal identity. And in order to have this dualism account coherent with the Aristotle’s framework in which the universe is made up of substances that have properties, we are in part forced to widen this framework to include a kind of “substance” other than matter, namely the soul-stuff. (As much as I wish to write more.)