What does it take for a person to continue to exist? Some say that the person must have the same body. Others say that the person must have the same psychology.

To see the difference, imagine that you step into a Star Trek-style teleporter. The machine will scan your whole body, and send that information over to a second machine located on a different planet. The first machine will then destroy your body, while the second machine creates a duplicate body. The person that comes out of the second machine will have all your memories. It will seem to them that just a moment ago they were on a different planet.

Teleportation illustration taken from: https://gypsy.ninja/scientists-able-teleport-particle-space/

In this story, what happens to you? Those who think personal identity consists in sameness of body will say that you cease to exist when the first machine destroys your body. The person that comes out of the second machine thinks and looks just like you, but they are a different person. Those who think personal identity consists in sameness of psychology will say that you teleport from one planet to another. The person that comes out of the second machine has a different body, but they are not a different person. They are you.

So, what does it take for a person to continue to exist? Sameness of body or sameness of psychology? One possibility is that there is no right answer—or, more precisely, that the right answer varies from person to person. If Manuel cares about sameness of body, then what it takes for Manuel to continue to exist is that he has the same body. So, Manuel cannot survive teleportation. But if Jimena cares about sameness of psychology, then what it takes for Jimena to continue to exist is that she has the same psychology. So, Jimena can survive teleportation. This is relativism about personal identity. What it takes for someone to continue to exist is relative to the person’s own conception of personal identity.

So far, so good. But what if someone’s conception of personal identity changes? Imagine that as a teenager, Kin cares about sameness of body. After he takes his first philosophy course, however, Kin decides that what really matters is sameness of psychology. Afterwards, he steps on a teleporter, which destroys his body and creates a duplicate body. In this story, what happens to Kin? Does Kin survive teleportation? Is the person that comes out of the second machine Kin? Relativism says: it depends on Kin’s conception of personal identity. But which one? The conception of his younger self, or the conception of his older self? This is the transfiguration problem for relativism.

Some relativists say: what matters is Kin’s conception at the time at which he steps on the teleporter. Since at the time, Kin cares about sameness of psychology, he does survive teleportation. But this seems like an odd thing to say for a relativist. After all, the guiding idea behind relativism is that there is no one conception of personal identity that’s better than the rest. But if what matters is the conception of Kin’s older self, doesn’t that suggest that this conception is somehow better than the conception of his younger self?

David Braddon-Mitchell and Caroline West (2001) suggest an ingenious solution. On their view, Kin’s story involves two people. There is a Kin-1 that continues to exist as long as he has the same body. But there is also a Kin-2 that continues to exist as long as he has the same psychology. Before the two Kins step on the teleporter, they share one body—f you shake Kin’s hand, you are shaking one hand, but saying “hi” to two people. When the teleporter destroys Kin’s body, Kin-1 ceases to exist, whereas Kin-2 simply teleports to a different location.

On this view, both conceptions of personal identity are correct. The conception of Kin’s younger self is correct with respect to Kin-1, whereas the conception of Kin’s older self is correct with respect to Kin-2. And, if Kin later adopted a different conception of personal identity, there would be a third person Kin-3 corresponding to that conception.