"I suppose, that personal identity cannot be contained within the history of choices that have been made, because for every choice that has been made, if it was truly a 'choice' at all, it was also made the other way in some other tributary of the Great Tao."

This might sound like a nitpick and a pet peeve, but in this case I think it's important and essential: Your decisions do not split you. At least, not in the way one would naively expect.

See Thou Art Physics: To the extent one make choices at all, one does so in a deterministic manner. When one is on a knife's edge, it's natural to feel like one's decision is indeterminate until one actually makes a decision, but that doesn't mean it's not determined by one's decision process. I don't know to what degree typical decisions are deterministic. Reasons can move one to action, but one's true reasons for action are obscured by later rationalization. It may be possible to control the degree to which one's decisions depend on quantum indeterminacy. If there's a lot of indeterminacy, it might be best to think of identity as a probabilistic computation instead of a deterministic one.

One's decisions can also depend on quantum indeterminacy in the environment, some of which might be mediated by millisecond delays in one's nerve firings. I don't know very much about this. This is the kind of thing that might turn Shen into a miser. But note that Shen's environment might deterministically make Shen a miser, depending on their disposition.

There is also a chance that otherwise deterministic computations in one's head can be occasionally frustrated by freak quantum tunneling events. But this accounts for a very small amount of amplitude, and you could think of it as overriding one's decision process (like an aneurysm would), rather than part of one's personality.

This subject warrants a lot of discussion — I'm not an expert, please correct me if I said something incorrect — but I don't think it has much bearing on the question of what identity is.

"Ah, but then which conscious awareness do you wish her to have? There is no copy; all possible tributaries of the Great Tao contain an original. And each of those originals experience in their own way. You wish me to pluck out a {configuration} and present it to you, and declare "This one! This one is Ah-Chen!". But which one? Or do you leave that choice to me?"

The one where she miraculously recovered from smallpox unscathed, all those years ago.

But which one?

What do you mean? Are you yourself, right now, one person? You are not a fully constrained decision process. An infinitude of possibilities lie before you.

Why, then, do you insist that I pick out one Ah-Chen? She was, like you are, a fuzzy process. Do not limit her possibilities and strip her of her choices! I do not ask for a single point in process-space, I ask for Ah-Chen, as she was before the disease, brimming with opportunity.

What is the purpose to making any sort of distinction between the identity of one person, and the identity of another?

On a practical level, it often seems to have something to do with people being more willing to work harder for the benefit of people they identify as 'themselves' than they would work for 'other people', such as being willing to do things that are unpleasant now so their 'future selves' will enjoy less unpleasantness.

Out of the various people in the future who might or might not fall under the category of 'yourself', for which of them would you be willing to avoid eating a marshmallow now, so that those people could enjoy /two/ marshmallows?

When I imagine resurrecting loved ones, what makes me believe that even a perfectly preserved brain state is any more 'resurrection' than an overly sophisticated wind-up toy that happens to behave in ways that fulfill my desire for that loved one's company?

Nothing. It's just a question of definition, and social consensus hasn't set one yet. My answer is that, if the past version of said loved one would have considered this being as themselves, then I too can consider this being as them (at least in part).

When I imagine being resurrected "myself", how different from this 'me' can it be and still count?

Again, that's up to you - this is a question of what you desire, not of what reality is like. My quick answer is that the resurrected being must have all all the first order desires and values of my current self, as well as retention of key knowledge and memories, for me to consider it "myself". Any changes in desires and values must be changes which could potentially be brought about in my current self strictly via non-neurologically damaging experiences, for it to still be "me" (and I'd hesitate to define these mutable sorts of desires and values as "first order"). Additionally, the cognitive style must either be roughly similar to my current cognitive style, or superior to it, but not inferior in any major metric.

So basically, I define myself by my preferences ("utility function"? emotions?), my experiences("priors"?, memory, knowledge, acquired skill?), and my mental abilities ("rationality"?, innate talents, cognitive style?). I think "personality" is probably contained in those three...

"Umm... that... let me think. I suppose, that personal identity cannot be contained within the history of choices that have been made, because for every choice that has been made, if it was truly a 'choice' at all, it was also made the other way in some other tributary of the Great Tao."

I don't like that part at all. As far as I understand those things, just now almost all of your measure/amplitude/whatever went into the version of you that didn't spontaneously stand up and jump out of the window and the difference between that and what would happen in a completely deterministic universe (in which you also wouldn't have jumped) doesn't seem very important.

In fact, I think that the less determined your actions are, the less they are 'choices'. Not jumping out of the window because a quantum coin came up heads may be more 'free' in some sense but if its independent from your past mental states then it's not really something 'you' do.

You say this is adapted from a 16th century story.

I find this story strange and unusual, for that age, but you have adjusted it to fit Lesswrong. Is there a more direct translation available?

If you want your resurrected self to be "you," then it's up to you to decide if your values are satisfied. A soul is something you made up. You are not barely aware of something simple and fundamental. The heuristic you use is not an approximation for something nicer. It's just what it is. If you value having simple and elegant values, there's not much you can do besides abandoning that one altogether.

If you just want to know what you would consider your resurrected self, because you have never been in that situation so you're not sure what you'd think, I'd say most of it is about memory. If someone with a completely different personality inherits your memory, I think they'd probably think of themselves as "you". Similarly, if your memory was replaced with someone else's, you'd start thinking of yourself as them. You would have a different personality, but you'd likely think of it as having changed, not being someone else altogether. That's just my guess, though.

If you want to resurrect a loved one, you should probably restrict them to also having a similar personality.

Thank you for the story. It succinctly describes my stance on identity, and similarly describes my frustration with people who do not understand the lessons in the story.

1) Who cares if it's a wind-up toy or not, if it provides indistinguishable outputs for a given set of inputs? Does it really matter if the result of a mathematical calculation is computed on an abacus, a handheld calculator, in neural wetware, or on a supercomputer?

2) Where you draw the line is up to you. If you have a stroke and lose a big chunk of your brain, are you still you? If you're reduced to an unthinking blob due to massive brain damage, is that still you? It's up to you to decide where you draw the line, so long as you recognize that you're putting it in an arbitrary place determined by you, and that other people may decide to put it elsewhere.

A good set of thought experiments that helped me work through this is to imagine that you have a magical box you can step into that will create a perfect copy of you. Said box will also magically destroy copies that enter it and press the 'destruct' button.

• What mindset would you need to have to be able to properly use the box?

• Under what circumstances would be able to create a copy, then enter the box and press the destruct button yourself?

"You have indeed learned much. But you still have not described the purpose of your boundary-drawing. Do you wish for Ah-Chen's resurrection for yourself, so that you may feel less lonely and grieved, or do you wish it for Ah-Chen's sake, so that she may see the world anew? For these two purposes will give us very different boundaries for what is an acceptable Ah-Chen."

Poor Shen Chun-lieh should have just said he wanted the {CEV} of Ah-Chen + Shen-Chun-lieh.

I don't think anything less than CEV or equivalent will actually pinpoint individual identity sufficiently well that we will have no complaints about resurrecting people from the best information available. If I had to manually pinpoint my own identity I would accidentally carve off entire swaths that I don't even know I have and distort the other parts. The physical description of my body at the planck scale is too limited; I would never change. Au-Chen brought back from the dead perfectly would be a little girl dying of smallpox; curing the smallpox would destroy her planck-scale identity. I don't know what level of accuracy is sufficient. I can only assume that it's somewhere between planck scale (or even atomic scale) accuracy and the mess that is ~80 years of gene-driven growth and change of a human body.

I think war raged within Shen's heart right at a key point of this.

I think to resolve resurrection, you may first have to resolve mind control. Because in cases like this, the person who is doing the resurrection is given mind control powers over the person who is dead. As a good example of this, I think I can regenerate most of the dilemma without any physical death at all:

Example: Assume that you and a loved one are the only people who can stop a terrible apocalypse. There is a mad scientist in the next room, the final obstacle to saving everyone. He has a ray gun that makes people simpletons.

Thankfully, there are two of you, and one of him. You've been planning strategies, and after discarding several that are distinctly suboptimal, here is your best bet:

1: You and your loved one enter the room, both begin aiming at the scientist. 2: The mad scientist fires his quicker simpleton gun, hitting one of you. The other one shoots the scientist, stopping him, and then stops the apocalypse. 3: However, the unhit person is left with the duty of reestablishing their loved one's thought processes from a simpleton.

In this case, physical death doesn't even seem to enter into it, and you still seem to have to resolve that feels to me like an incredibly similar set of conundrums, most of it focused on "Someone needs to rebuild someone else's utility function, metautility function, etc... and you may be either of the two people in this scenario."

Does that sound reasonable?

Excellent job on this post! It is very well written with some awesome & very memorable passages. (And it's going to make me think about the nature of identity way too much over next few days... :)

I watched a couple lectures from this course. It really helped me approach the issue of identity (and death) from a new perspective. Specifically, I think memories are the defining characteristic of identity.

From my recall, Kagan gave the example of someone who lived forever, but whose memory was fully erased every X years. Who would they be at any given moment? It seems to me, in that case, they would lose identity each time their memories were fully erased. You'd have a completely new person after each "reboot". Even if personality and every other aspect of identity were perfectly preserved, memories are the key in my view. (It seems really obvious to me now [and maybe it is really obvious to most people], but I remember it shifting my understanding pretty significantly at the time I first encountered the idea.)

I've got nothing to contribute, other than that this story really helped resolve some personal crises on identity. This part especially:

"Even now, you are not quite correct. The soul is not a {computational process}, but a {specification of a search space} which describes any number of similar {computational processes}. For example, Shen Chun-lieh, would you still be Shen Chun-lieh if I were to cut off your left arm?"

Thank you for writing this.

I may be kidding myself, but I think of my identity as being at least as much tied up in something about how my experience usually feels as it's tied up with my memory.

I do care a lot about my knowledge of golden age sf, and was upset when I lost access to it after trying welbutrin briefly. (I don't know how often this sort of thing happens, but it damaged my access to long term memory for months. It was bad for my short term memory, too.) However, I think I'd still be me in some important sense if I cared about something else the way I care about sf, and wouldn't be me if I cared about sf in some other way. This is getting hard to define, because when I think about, I'm not sure about other ways of caring about sf. There are other people with much better memories of the details, and I wouldn't mind having that. I'm pretty sure I'd still be me if I could put a lot of work into trying to figure out who Severian's parents are. (Gene Wolfe, Book of the New Sun). I'm not sure I'd be me if I developed a huge preference for science fiction vs. fantasy or vice versa.

Here's one: a major thing I want from sf is the feeling of spending some time in a world which is different from and more interesting than this world. I can enjoy nitpicking the world-building, but it's not a primary pleasure.

A while ago, I tried D-phenylalanine, and I dropped it because I didn't feel like me. Sorry, too long ago to remember details.

I have a sense of rightness which drives the way I do calligraphy. I wouldn't want to lose that, but having a sense of rightness is an important part of how I approach creativity and I'd want to have something else it applied to. I'm not sure everyone else does it that way.

It's not that memory or physical continuity are nothing to me, but I can tell I'm me because I feel like me. If I became someone who found their identity in their memories, I'd be someone else. And if you resurrected someone who looked like me and did calligraphy like me, but who found their identity in their memory, you've gotten it wrong, at least by my standards. Not that the pseudo-me would necessarily care, and I'm not sure about whether you're obligated to care.

Possibly one of the ways you can tell I'm me is that I'm not taking a crack at the possibly harder question of what you'd want from resurrecting someone else.

Both questions seem to boil down to the hard question of continuity-of-consciousness. When I say I want someone resurrected, I mean that I want the do-what-I-mean equivalent of pressing "play" on a paused movie: someone resuming their life as if they had never left it.

Excellent post.

I have pondered the same sort of questions. Here is an excerpt from my 2009 book.

My father is 88 years old and a devout Christian. Before he became afflicted with Alzheimer’s he expected to have an afterlife where he would be reunited with his deceased daughter and other departed loved ones. He doesn’t talk of this now and would not be able to comprehend the question if asked. He is now almost totally unaware of who he is or what his life was. I sometimes tell him the story of his life, details of what he did in his working life, stories of his friends, the adventures he undertook. Sometimes these accounts stir distant memories. I have recently come to understand that there is more of ‘him’ alive in me then there is in him. When he dies and were he to enter the afterlife in his present state and be reunited with my sister he would not recognize or remember her. Would he be restored to some state earlier in his life? Would he be the same person at all?

I originally wrote this to illustrate problems with the religious idea of resurrection. I now believe that this problem of identity is common to all complex evolving systems including 'ourselves'. For example species evolve over their lifetime and although we intuitively know that we are identifying something distinct when we name a species such as homo-sapiens the exact nature of the distinction is slippery. The debate in biology over the definition of species has been long, heated and unresolved. Some definition referring to species are attempts along the line of interbreeding populations that do not overlap with other populations. However this is a leaky definition. For example it has recently been found that modern human populations contain some Neanderthal DNA. Our 'species' interbred in the past, should we still be considered separate species?

"Is it really Ah-Chen?" is a question of value, which is up to Shen Chun-lieh in the first place.

That he, or we, have value algorithms that get confused and contradictory in situations that humans have never faced is hardly surprising .

Values are choices. Identity masquerades as a fact, but it is fundamentally about value, and therefore choice as well.