Analyze Derek Parfit's Personal Identity

This essay will analyze Derek Parfit’s Personal Identity. In his essay, Derek Parfit explains a scenario where a brain is divided into two pieces. The two pieces of brain are then housed in two different bodies. 1 To Parfit, there are three possibilities for the survival of the identity to which the brain in question originally had. 1. The person’s identity does not survive. 2. The person’s identity survives as one of the two new people. 3. The person’s identity survives through both new persons.

Parfit rejects all three of these possibilities for various reasons.

I will attempt to explain how Parfit goes about rejecting these three possibilities, and explicate what I believe Parfit overlooked. In his essay Parfit rejects the first possibility by bringing up a person who has lost half his brain. He says that it is possible for people to have half of their brain destroyed and still survive. 2 This being the case there is little difference between having half a brain transplanted and having half a brain destroyed.

Either way the person still only has half a brain. Parfit also rejects the second possibility. In the second possibility the person survives as one of the two new people.

Parfit’s rejection is based on both halves of the brain being identical. If both halves of the brain are identical, and both are transplanted successfully, then there is no reason for one to survive and the other not too. The third possibility is more difficult to resolve. Parfit rejects the notion of the survival as two people.

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If survival consists in the sameness of identity, then it doesn’t follow that a person can survive in two people and have the same identity. On the other hand it may be possible for one person to have two bodies with a divided mind.

3 Supposing that the two people were separated for a long enough time, it stands to reason that they may end up different people. 4 This is where a major problem occurs. If possibility three is possible, it is only possible if a person survives as both new people. Parfit has rejected this claim. But he also says that two people could survive and be different. Parfit then tries to resolve this discrepancy. He brings to example two people who make up a third person. The two people can be themselves, but also comprise another person. 5 Even this doesn’t seem to resolve the issue.

Parfit then raises another possibility; he attempts to separate survival and identity. In other words one could survive as the two different people without being those people. This concept he calls the “descendant self”6, whereby a person doesn’t necessarily have the same identity as either of the resulting persons. Rather, the two resulting people together make up the person. So it seems that Parfit is skirting the original question of identity. His theory of the “descendant selves” attempts to remove identity out of the problem and replace it with survival.

I don’t believe that Parfit feels identity is a necessary component in survival. Furthermore, by taking this stance, I don’t think that he answers the question of personal identity. Clearly though only parts of one’s body needs to survive, and I think that Parfit would agree that that is the brain. This being the case Parfit brings to example a person with epilepsy. Doctors can split the brain and create “two separate sphere’s of consciousness”. The separation of the two halves of the brain doesn’t seem to matter, as long as they are in the same body.

If the two brain halves are in the same body then that constitutes the same person. But what is the difference between being in the same body and not being in the same body? The only difference is that the separated halves are in different bodies. Parfit objection would be that the two people could be separated for a long period of time they would end up being different people. They may not even recognize each other if they met. Still, it doesn’t mean that they are not the same person. If me right now and me sixty years from now met, we may not know or recognize one another.

Is that to say that we aren’t the same person? I don’t think that Parfit is truly interested in the problem of personal identity per se. Rather, I think that he is more interested in explaining survivability. In that it doesn’t matter to Parfit that the original person survives, instead, what is important is that someone survives. Furthermore, that “that someone” has some relation to the original person’s psychology. Moreover, that the psychological relationships are continually overlapping. 7 These overlapping relationships Parfit calls “psychological continuity”.

I don’t think that this idea of psychological continuity solves the problem of personal identity though. If we look at Parfit’s diagram, we would see the original person “A”8, and several “descendant selves”. 9 These descendant selves are connected to person “A” through psychological continuity. In this way, any person on the tree is a descendant self of “A”. Moreover, though these people may not be person “A”, and in fact are not person “A”, still they survive “at best” as part of person “A”. This is somewhat difficult to understand. The descendant selves are not the original person.

If this is the case, how does Parfit answer the question of personal identity? The answer is that he doesn’t. Or rather, that he skirts the issue. Parfit makes survivability the important issue. How is it that someone can survive into the future? Even though there is no one identical to you in the future there is psychological continuity between you and a future self. This being the case, survivability is a function of psychological continuity. This is where I think Parfit’s mistake is. Continuity, to me, implies an uninterrupted succession or flow. I believe the key word here is “uninterrupted”.

Yet, in Parfit’s example there is an interruption. Between each of the descending selves exist differences, which create a separation. Another way to think of this is to use Parfit’s original example of the brain surgery. Suppose we had three people, and two of those people had their brains removed. Further suppose that we took the brain of the third person, split it half, and transplanted the halves into the two people without brains. The third possibility (which Parfit rejects) would say that the original person’s identity survives through the two new people.

What Parfit wants to say is that the two new people are descendant selves of the original person. Furthermore, that the two new people share psychological continuity with the original person. Though they are not the same people as the original person, the original person survives through them. Herein lies what I believe to be Parfit’s mistake. The two new people do not share psychological continuity with the original person. Continuity, as stated above, implies an “uninterrupted” succession or flow. To say that a person’s psychology is continuous through the type of operation stated before isn’t true.

Having one’s brain cut in half already implies that one wouldn’t be the same person. If this were the case then personal identity wouldn’t be the same either. Though some of the original person’s memories and traits may survive, the original person’s identity wouldn’t. Ultimately, if the two new people created only share some memories and some traits of the original person, I don’t think that it is enough to say that they share psychological continuity with the original person. This being the case, it also wouldn’t follow that the original person survives through the two new people. A few memories and traits don’t constitute survivability.