Parfit argues that questions about personal identity do not necessarily have determinate answers. He does so by asking us to consider a spectrum of cases in which a person changes in a variety of ways.
Let’s call the person before the changes are made A and the person after the changes have been made B. After considering each change, we can ask “Is A the same person as B?” In many cases, the answer will be “yes” or it will be “no.” The conclusion Parfit hopes to establish is that there are some changes for which it is equally appropriate to say “yes” or “no” or even “yes and no.”
Parfit starts by repeating Williams’s argument. That’s what his “psychological spectrum” involves: a series of minute changes to a person’s mind. If you would survive one such change, it seems, you would survive them all, even to the point where your mind is completely different. That suggests personal identity is the same thing as bodily identity: you stay with your body even though your mind has been completely altered.
But things are not so simple. What if we did something similar with your body? In the “physical spectrum,” we imagine a series of minute changes to a person’s body. If you could survive one such change, it seems, you would survive them all, even to the point where your body is completely different.As in teletransportation, for instance. That suggests personal identity is the same thing as psychological identity: you stay with your mind even though your body has been completely destroyed.
An inquiring mind might ask “what if we combined them?” OK, what if we did that? Imagine a series of minute changes to your body and mind. The person at the far end of the spectrum would have a body and mind like that of Greta Garbo.
Would you be the same person as the Greta Garbo person? Parfit doesn’t think so. There is nothing left of you: both body and mind are gone.But what about an immaterial soul? That tells us there is something fishy about these spectrum experiments.
Most of us would have felt pretty good to have come that far. But Parfit has far too original and searching a mind to have stopped there.
We have two points that seem pretty solid.
That’s a bit of a head scratcher. Some of the changes on the Combined Spectrum must be enough to kill the person on the left side. But no particular change is enough to make the difference between remaining alive and dying. What do we make of this?
Parfit’s proposal is that there are a range of changes for which it would be indeterminate whether the original person survived the change. That means it would not be definitely true that the original person was identical with the changed person and it would not be definitely false.
Franklin proposed a very helpful analogy with colors. Take two colors: red and orange. There is a spectrum here too. Start on the left: it’s definitely red. You can add a minute amount of yellow to red and it will still be red. If you add a lot of yellow to red, the color will be orange. The color on the right side is definitely orange. But somewhere in the middle, there are colors that are sort of red and sort of orange. They aren’t either red or orange, mind you. So you can’t say they are the same color as red. And you can’t say they are not the same color as red. There is no fact about whether the colors in this zone are red or not. The only facts are the proportion of red and yellow in them.
Here’s a way of summarizing Parfit’s view. There isn’t anything for a person to be other than a body or a mind. But both physical and mental continuity can come in degrees. So there have to be cases in which it is indeterminate whether the original person survives some changes. By analogy, the amount of red in a color comes in degrees and that is why there can be cases in which it is indeterminate whether a given color is the same as red.
There is, of course, an alternative. If personal identity consists in the identity of an immaterial soul that cannot be divided, then we wouldn’t be driven to this conclusion.
I understand everything about Parfit’s line of reasoning. But I can’t get past the following argument that I take from Williams.
Maybe I should believe in immaterial souls!
We had yet another extremely good discussion of this. Here are some points I jotted down.
Ian had an argument that seems to prove there can’t be a sharp line between survival and death on any of these spectra. Pick almost any sharp line you like, and most of us will cross it during our lifetimes: we undergo lots of physical and psychological change in our journey from infancy to old age, after all.
Kai said in response that he thinks it makes a difference whether the change is gradual, as it is in real life, or sudden, as it is in Parfit’s examples. If so, these examples might be misleading.
Josh noted that if there are indeterminate areas on a spectrum, then the border between the indeterminate and determinate areas has to be indeterminate as well. And that’s just hard to understand. Does it mean that the whole thing has to be an indeterminate zone? I cited the title of the course to get out of that one!
Finally, Kai said something after class that struck me as very interesting. He said that what happens in the indeterminate part of the Combined Spectrum is that part of me sees the white room. By analogy, if one of my memories is transferred to another person, that would be part of me in a new mind. Why is it so much harder, he asked, to imagine part of me experiencing (part of?) what a new mind experiences?
And I have to confess that I don’t know.
When I first taught this course here, one of the student evaluations said something like “it was like we were all pros.” You should feel the same way.
The New Yorker published a profile of Parfit in 2011.Larissa MacFarquahr, “How to Be Good,” The New Yorker, September 5, 2011. You can’t read it without a subscription, but you can see a picture at the bottom of the page.