IS PERSONAL IDENTITY WHAT MATTERS? by Derek Parfit 31 December 2007

In my book Reasons and Persons, I defended one view about the metaphysics of persons, and also claimed that personal identity is not what matters. In this paper I shall give some further arguments for this second claim, and also try to respond to some forceful objections by Mark Johnston. I shall not, however, try to decide what does matter, since that is a much larger and more difficult question. 1

PART O NE
1 The Metaphysics of Persons 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 Teletransportation 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. That is a disagreement about personal identity. To understand such disagreements, we must distinguish two kinds of sameness. Two 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 a different colour, it will cease to be qualitatively identical with itself as it

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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