Author’s Introduction (Full Text)
- We can start with some science fiction. Here on Earth, I enter the Teletransporter. When I press some button, a machine destroys my body, while recording the exact states of all my cells. The information is sent by radio to Mars, where another machine makes, out of organic materials, a perfect copy of my body. The person who wakes up on Mars seems to remember living my life up to the moment when I pressed the button, and he is in every other way just like me.
- Of those who have thought about such cases, some believe that it would be I who would wake up on Mars. They regard Teletransportation1 as merely the fastest way of travelling. Others believe that, if I chose to be Teletransported, I would be making a terrible mistake. On their view, the person who wakes up would be a mere Replica of me.
First Two Pages of Section I (Full Text2)
- That is a disagreement about personal identity. To understand such disagreements, we must distinguish two kinds of sameness. Two white billiard balls may be qualitatively identical, or exactly similar. But they are not numerically identical, or one and the same ball. If I paint one of these balls red, it will cease to be qualitatively identical with itself as it was; but it will still be one and the same ball. Consider next a claim like, 'Since her accident, she is no longer the same person'. That involves both senses of identity. It means that she, one and the same person, is not now the same person. That is not a contradiction. The claim is only that this person's character has changed. This numerically identical person is now qualitatively different.
- When psychologists discuss identity, they are typically concerned with the kind of person someone is, or wants to be. That is the question involved, for example, in an identity crisis. But, when philosophers discuss identity, it is numerical identity3 they mean. And, in our concern about our own futures, that is what we have in mind. I may believe that, after my marriage, I shall be a different person. But that does not make marriage death. However much I change, I shall still be alive if there will be someone living who will be me. Similarly, if I was Teletransported, my Replica on Mars would be qualitatively identical to me; but, on the sceptic's view, he wouldn't be me. I shall have ceased to exist. And that, we naturally assume, is what matters4.
- Questions about our numerical identity5 all take the following form. We have two ways of referring to a person, and we ask whether these are ways of referring to the same person. Thus we might ask whether Boris Nikolayevich is Yeltsin. In the most important questions of this kind, our two ways of referring to a person pick out a person at different times. Thus we might ask whether the person to whom we are speaking now is the same as the person to whom we spoke on the telephone yesterday. These are questions about identity over time.
- To answer such questions, we must know the criterion of personal identity: the relation between a person at one time, and a person at another time, which makes these one and the same person.
- Different criteria have been advanced. On one view, what makes me the same, throughout my life, is my having the same body. This criterion requires uninterrupted bodily continuity6. There is no such continuity between my body on Earth and the body of my Replica on Mars; so, on this view, my Replica would not be me. Other writers appeal to psychological continuity7. Thus Locke claimed that, if I was conscious of a past life in some other body, I would be the person who lived that life. On some versions of this view, my Replica would be me.
- Supporters of these different views often appeal to cases where they conflict. Most of these cases are, like Teletransportation8, purely imaginary. Some philosophers object that, since our concept of a person rests on a scaffolding of facts, we should not expect this concept to apply in imagined cases where we think those facts away. I agree. But I believe that, for a different reason, it is worth considering such cases. We can use them to discover, not what the truth is, but what we believe. We might have found that, when we consider science fiction cases, we simply shrug our shoulders. But that is not so. Many of us find that we have certain beliefs about what kind of fact personal identity is.
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