Parfit and the Selves That Matter

10 April 2023

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.

Comments (6)

Tim Smith's picture

Tim Smith

Friday, April 14, 2023 -- 2:23 PM

Dave Edmond's book isn't out

Dave Edmond's book isn't out for another few days, but he has been on Philosophy Talk before ( and has even written about Parfit - elsewhere ( If one is interested, there is plenty of stuff to read ( or listen to ( I took the opportunity of this show to pick up Parfit's book 'Reasons and Persons' as I had the book already, having supposedly read it before.

It turns out I hadn't read R&P before, not well, at least. Reading is always different, depending on your time and place and the emphasis you bring with your attention. This recent moment was very other than the moment I had brought before and is an afterlife that may last longer, but probably not. Parfit is perfect at either moment, early in life, or late. In this most recent time, however, I have come to understand something profound and life-affirming. The profundity is the tapestry of consolation implied in the unsigned blog above.

When Parfit died in 2017, NFTs were starting to circulate and hold value, and Blockchain laid the framework to digitize identity and contracts in the previous decade. There is more than enough fodder to spew a blog on that irony.

As Edmonds relates, Derek was on the spectrum and was loved and respected by those who took the time to understand his philosophy. Parfit lived that philosophy, and that is the deepness I alluded to above. It is inspirational and makes the goal of reading Edmond's book worthy of anyone's time.

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Daniel's picture


Friday, April 14, 2023 -- 4:42 PM

--Which presupposes that you

--Which presupposes that you can prove it. Otherwise how could such a comprehensive claim be justified? How can you speak for "anyone", which is equivalent with "everyone", with application to universal time-use value? Assuming that you're not lying, what are the grounds for this particular value judgement? Take the example of Kate the writer at the beginning of R & P. Her desire to create good books causes enough negative health effects to make the fulfillment of the desire produce greater adversity for her as an individual. While one respects her choice to write good books, it could not be recommended by another individual who doesn't. As one can imagine similar scenarios with large reading-commitments, which you obviously must have considered, how are they overridden by a time worthiness-universalization for this particular one?

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Tim Smith's picture

Tim Smith

Sunday, April 16, 2023 -- 9:40 AM

Here is a recent review of

Here is a recent review of Edmond's book ==> . The article is pay-walled and very short but does allow anyone to open it in reader mode or save it to reading sites like Pocket.

The reviewer is Carl Rollyson - who has a particular bent on biography and exercises his lens to pick at Parfit's idea of personal identity. He also recounts a storied interaction with Amia Srinivasan and alludes to Parfit's spectral need for capturing repetitive images and fixation on morality.

Another good read.

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Daniel's picture


Tuesday, April 18, 2023 -- 12:20 PM

You've hedged your bet.

You've hedged your bet. "Anyone should" has deflated into "one that is good". I surmise therefore that it was not through dishonesty that you chose an expression of universality for your recommendation, but merely that you had not bothered to consider its truth or falsity, and allowed your desire for praising the work to override your care for anyone who reads it.

A question arises however with regard to the relation of Rollyson's treatment of personal identity and your claim in the second paragraph of the 4/14/23 2:23 pm post above that survival of the individual is not temporally neutral and as such can only arbitrarily be defined outside of the time and place of particular emphasis furnished by one's attention. How does your example of reading-diversity across both the moment of assumption that something had been read, and the moment of discovering that it hadn't been, apply to the analysis of this scholar? Although both can without inaccuracy be called "reading", they are clearly different activities. Does the temporal non-neutrality of individual survival which is tied to attentional emphasis imply an agent-neutral account of survival-importance?

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Daniel's picture


Saturday, April 22, 2023 -- 4:32 PM

While professor Smith is out

While professor Smith is out on lunch break, perhaps it's a good opportunity to discuss the teleportation thought experiment invoked above. Let us alter it a bit though by saying that the replica on Mars is exactly qualitatively identical to the original individual on Earth down to every molecule except for one exception. One molecule must be added to the Mars version so that the trademark of the manufacturer can be embossed upon it, visible under an electron microscope, in order that a warranty be supplied in case of any defects. The Earth version however can have no such warranty on account of the fact that it has not been artificially produced, and any defects must be remedied within the context of terrestrial health insurance, whether state run or private. This means that over time, a given quantity of individuals on Earth would be composed of slightly less molecules than their duplicates on Mars, even if in each given case the added amount would be so small that it could not be perceived.

Then let's say that the quantity of ponderable matter in the universe is finite, as some physicists do, but its duration is infinite. Because a molecule which is added to something in a finite universe has to be taken away from something else, consistent use of the bio-teleport system, given an infinite amount of time, would absorb almost all the other matter in the universe so that all that remains would be the teleported individuals and the mistakes which didn't make it through which are not protected by the manufacturer's warranty. As anything edible would also no longer exist, what protects the remaining mistakes from being eaten by their manufactured duplicates? How could the manufacturer's liability protect the consumer in this case if what went wrong can not help make it right?

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Harold G. Neuman's picture

Harold G. Neuman

Saturday, May 20, 2023 -- 11:34 AM

There has been reference to

There has been reference to and opinions about Parfit, cloning, transhumanism and so on with other blogs I have read this month. Lots of differing views. Insofar as cloning, as I understand it, is (or was) different to the trekie notion of teleportation, I have not taken that discussion seriously. There are other conversations I have had regarding humanism and transhumanism that leave me equally nonplussed. Item: I did not know the humanist idea was 700 years old. That clears up a few things, while raising more questions. For me, anyway. Oh, and I had not mentioned it here, but part of my inquiry included Panpsychism, a cosmos-inclusive belief which has been around since Descartes.---and, ebbs and flows, at will. Or, according to interests, preferences and motives. Seems to me that when physics, biology and belief systems collide, there i s a stochastic, freeway pile-up of 'huge' proportions. Intersections, real or imagined, are dangerous places. Oracles are of no use. Even when they think. I'll ride along.

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