Monday, February 08, 2010
Am I different persons? Personal identity (23)
One of the problems discussed in the philosophy of personal identity is that body cells or body parts are artificially replaced by new cells or parts. For example it is Parfit’s case in which I am (or rather my brain and body is) teletransported to another planet with the help of a machine. Then, according to Tye in Consciousness and Persons, “I no longer exist” (p. 148). But he continues: “[W]hat happens to me, if 10 percent is replaced, or 35 percent, or 70 percent? Is there a fact of the matter about which partial teletransportation destroys me?” After some discussion Tye concludes that such a fact of the matter does not exist but “Once enough of the original neurons are replaced (and the originals simultaneously destroyed) a new brain is created and the resulting person is not me”. I’ll pass over here that Tye talked earlier about teletransporting brain and body and now suddenly only about the brain. Readers of my blogs will know that I see the identity of a person in the body as a whole (including the brain) and not only in the brain. But is it really so that we can say that if enough of my brain or body (including my brain) has been replaced, I no longer exist in the sense that the original person that I was has been destroyed?
What philosophers who discuss this theme always forget is that the replacement of cells and body parts is not only a philosophical thought experiment, but that it happens also in nature. For isn’t it so that damaged parts of the body can heal by replacing the damaged tissue by new tissue? Even more, isn’t it so that during my whole life my body cells are gradually and continuously replaced by new ones, while the old body cells are destroyed? But in the case of the natural replacement of my body cells nobody says that my personal identity is destroyed and that I have become another person with another identity after some time. If we would accept that, it cannot be without consequences. For instance, fingerprints do not change through the years, but after, say, ten years they would be the fingerprints of another person! Or take this: the mainstream of personal identity philosophers, who defend the so-called “psychological view”, state that a person’s personal identity remains the same as long as a person can still remember past facts of his or her life or as long as a person has remained unchanged in other psychological respects between some point of time in the past and the present. If a person has changed enough in psychological respect he or she is no longer the same, they say. However, if we accept that the replacement of my body cells makes me another person after some time, then it can happen that physically I am another person but psychologically I am still the same as before this replacement. And that sounds rather weird.
If we cannot accept that the gradual natural replacement of my body cells and body parts makes me another person, what is then the fundamental difference between this natural replacement of my body cells and parts and its artificial replacement by means of teletransportation, transplantation or which other artificial replacement we might invent in real or in our thoughts? For the latter replaces me by another person in the view of Tye and others, while the former does not in case there is a fundamental difference between both. But if there is no fundamental difference, either a big part of the discussion about personal identity must be done anew or it must be accepted that I am physically different persons during my life, even if my life is a psychological unity.