Parfit thinks that survival (not identity) is important to people. Peter Unger has questioned rather survival is really the important thing. He comes up with a counterexample to Parfit’s theory of survival. Imagine that you have a wife, husband or other special friend. Now, you have a choice. Either you can keep your same wife, husband or special friend or this person is transported to another world and you are given a duplicate of your partner. To spice things up, you get a cash reward if you choose the duplicate. Unger thinks that clearly we will want to keep our same partner or friend. Unger notes that we care about individual particular people, not just bundles of properties and personalities. Because of this, Unger concludes that we care about identity, not survival.
Robert Nozick characterizes Parfit’s theory of personal identity as a no-rival theory. This is because Nozik does not allow for fission cases because when one person turns into two people, there are two equally good rival candidates who can possibly carry on the identity of the original person. In other words, he excludes possibilities where there are rival candidates for identity. Xander can only be identical to Yunker if there is not an equally good candidate, Zorro who is just as psychologically continuous with Xander and Yunker. Nozick thinks that Xander and Yunker can be identical even if there is a rival candidate Zorro who has the same amount of psychological continuity to Xander and Yunker as Xander and Yunker have to one another. Nozick provides what he thinks is a better alternative than a no-rival theory.
Robert Nozick’s Closest Continuer Theory. Imagine that Larry is a copy of (identical to) Moe. A day or two later, Curly is also made as a copy of Moe. Nozick thinks that Curly can be identical to Moe, too, if Curly’s connection to Moe is the same or better than Larry’s connection to Moe. Nozick’s theory does not specify that the connection between Larry and Moe must be psychological.
Nozick uses some cases to test this theory.
#1. Imagine that you are perfectly cloned. There are two individuals exactly like you. The question is: which one is you? Nozick says that you are still you because the clone is not the closest continuer. The connection that you have to yourself is stronger than the connection that the clone has to you. After all, you are you and your clone is just your clone.
#2. Imagine that you are perfectly cloned and then you slowly die. Nozicks says that when you die, you become your clone. Your clone is your closest continuer once your original body and mind are gone. Someone might be inclined to say that this is silly, since original me is living simultaneously with the clone, I am me, not the clone. While I am still alive, the clone is not the closest continuer, so how can it be that the clone is the closest continuer at a later time? Nozick thinks that the closest continuer may be a different individual at different times. Nozick says that ultimately, you choose whether you become the clone or not. This will depend on whether you consider a very long time span or only a short time span.