The works of Derek Parfit (1942-2017) have had a profound influence on how philosophers understand rational decision-making, ethics, and personal identity.
Derek Parfit was a really interesting thinker when it came to identity and the self. He had a particularly cool thought experiment involving tele-transportation.
Suppose you’re on your daily commute to Mars. You’re about to get beamed up, but something goes wrong—the transporter makes a copy of you on Mars, like it’s supposed to, but it forgets to vaporize you back home. So now there are two of you. And if there are two of you, the question is which one is the real you—the you on Earth, or the you on Mars?
To some the answer seems obvious: it’s the original you on Earth. After all, imagine if the teleporter malfunctioned a different way, and didn’t create a copy on Mars. You’d just happily go about your business down here. Of course when the transporter is functioning normally, you disappear down here and materialize on Mars. So by that logic the Mars you is the real you. Could both be the real you?
Parfit says no. Suppose your Mars self sets up an oxygen factory and marries the boss of the Thunderdome. Meanwhile, your Earth self hangs out at a surf shop on Bondi Beach. These two people are living totally different lives and can't possibly be the same person. So maybe one of them is you and one of them isn’t—does it even matter?
Perhaps you might not care in that scenario. But suppose the Earth version of you only has one day to live, and the Mars version is going to live long and prosper. Wouldn't you hope in that case that the Mars version is the real you? You'd certainly want to know whether you're in for a long happy life or certain death. But it seems like there’s no way of knowing—it’s not like you can just ask them, since both would claim to be the real you, both would look like you, remember my childhood, etc. Even your family and friends would probably be confused.
These are all cool questions, but Parfit ends up saying something even more interesting. He thinks it doesn’t even matter who the real "you" is—his slogan was "identity is not what matters."
But shouldn’t identity matter? Most of us were very different as 20-year olds than we are as older adults but still feel responsible for the dumb things we did in our youth, because we're still the same person. And we really care about what’s going to happen to us in old age because that’s going to be us too. Parfit thinks we’re right to care about our past and our future—but not because you’re literally the same person.
But aren’t you literally the same person? You’ve got the same name, you’ve been dragging this body around the whole time, you've got (more or less) the same likes and dislikes. Fine, but that’s not the thing that matters: what matters is that you can remember the stuff your 20-year old self did, and you can count on your 70-year-old self to carry out some of your plans. Plus you have a lot in common with those people: you like a lot of the same music, you have similar personalities, you even look related.
Of course, you also have some of those things in common with people who aren’t you—and Parfit says you should care about them too. That’s exactly what’s so powerful about this way of thinking. Suddenly you stop being so self-centered and start seeing yourself as just another thread in the tapestry of human life. You might even become less afraid of death.
If this all sounds difficult to believe, our guest may be able to help (assuming it's really him and not his replica from Mars): David Edmonds, a former student of Parfit's and author of a new philosophical biography, Parfit: A Philosopher and His Mission to Save Morality.