well, what exactly do you mean by "the same"?

When we ordinarily say that two things are the same, aren't we merely implying that we can substitute each for one another for some intended purpose?

Suppose we have no purpose for visually comparing two photographs. Is it even meaningful to ask ourselves "are they the same"? For what is the criterion of sameness here, and to what purpose is it being put to?

Perhaps in absence of any criteria of sameness, we might say they look the same, but are we really expressing a truth regarding their appearance to us, or are we merely expressing our ambivalence towards them?

If we were expressing a truth of their appearance to ourselves, wouldn't we would have to be literally superimposing their images on top of each other in our imagination?

and even if we could do that, wouldn't we still need some external criteria of correctness to compare our judgement against? for otherwise we wouldn't be asserting anything and would merely be creating a private definition to ourselves for the meaning of "looking the same to me" which would assert nothing positive or negative to ourselves in an epistemological sense.

So if self-identity over time is a concept analogous to judging the appearance of photographs with no external criteria of correctness, it is a meaningless concept.

On the other hand, if one is asking whether one is physically and functionally the same over time, the answer depends on the scale we are employing for our criteria of sameness, which is normally chosen according to our intended purpose.

I have the solution to this problem. I'll repost what I posted in another thread in response to Purple Pond.

I realize it is a strange idea that I am asking you to consider. Bear with me a bit and keep an open mind and consider the following. It is long, I know, but I don't know how else to get this across. If you get what I am trying to communicate, I think you'll see that it neatly solves all of the many puzzles of personal identity is a possible solution almost always left unconsidered.

Have you ever wondered why you find yourself being the particular person you happen to find yourself being? Don't look at it from an objective standpoint. Look at it from a subjective standpoint. Ask yourself, "Isn't it a little odd that I happen to find myself being Purple Pond and not someone or something else?"

First, consider that having a subjective perspective and being someone isn't an objective state of affairs. If you were to restrict yourself to third-person language and describe the world, there is one thing you couldn't declare: which of the entities in the world you are. You could say things like "Purple Pond is sitting in a chair looking at a screen" or "Oysteroid is wearing a white sweater" or "Purple pond says that he is Purple Pond". You couldn't say "I am Purple Pond." Finding yourself as a particular person, occupying a particular perspective, is something other than an objective fact, something that reveals itself to be more than a little mysterious if you think about it for a while.

What are the odds that out of all of the 3 pound hunks of matter out there in the vast universe or maybe even infinite multiverse, most of them lacking biology, you just happen to find yourself being a human in this special place and time? Did you win the cosmic lottery a hundred times over or something? Shouldn't you find it a bit surprising that you find yourself occupying such a privileged vantage point on the world? After all, it seems, you might have been a mouse instead, or a bacterium, or a cloud of dust or a rock in outer space.

Suppose we have a big bucket filled with a trillion marbles, one of which is gold, the rest of which are blue. We blindfold you and have you dig around and withdraw a marble. Then we ask you whether or not you should expect to take off the blindfold and find yourself holding a gold marble. Of course, the answer is no. With a random sample, you should expect to have a typical sample. If you do end up finding yourself with the one in a trillion golden marble, shouldn't you find this surprising?

Now consider how rare life is, how rare brains are, as far as hunks of matter go. Even as far as brains go, human brains are extremely rare. Even if the only thing it is possible for a self to find itself as is a human brain, isn't it weird that you are this particular one, and not another? What is it that determines which vantage point on the world you have?

From an objective perspective, of course Purple Pond is Purple Pond! How can it be otherwise! A is A! But that ignores the issue. The issue is your subjective perspective and your being someone.

People say, "I am my brain." What does that really mean? They are connecting something, their 'I', to something else, a particular brain, and saying that A is B. Isn't this a bit odd? What is this 'I'? To be a truly separate individual, it is as if you have your own 'I' and I have another one, as if each brain has a unique 'I' associated with it. But this idea, resembling the old individual soul idea, just adds mystery to mystery. Suppose you are a soul, even if you don't believe in such things. Why are you this soul and not a different one? Same problem. And on you would go with an infinite number of homunculi within homuncili.

Consider further what a strange idea it is that you can be something, some arbitrarily extended, but limited, collection of physical particles. People sometimes ask what it must be like, if it is like anything at all, to be a rock. Notice what they are doing! Is there some magical boundary around a rock other than the one we impose when we see a rock and identify it as such, mentally separating it from its surroundings? If a rock, which is a collection of many smaller things, why stop the collection at that point? Why not a pile of rocks? Why not the mountain? Why not the planet? Why not the whole universe?

But isn't it strange that you could be a collection of things in the first place? Let's simplify this so that the issue becomes more clear. Suppose you were to find yourself being a thing that is composed of exactly two things, perhaps two quarks. How can you be a pair of things? Isn't that a weird idea? How is it that you have this span, that what you are can extend beyond just one thing to include more?

Gilbert Ryle used to talk to his students about the question of whether there are three things in the field, two cows and a pair of cows. This makes me chuckle.

When people claim to be a brain or a whole body or whatever, they are saying that they are a huge collection of things, that their identity has this incredible span. Why not half the brain? Why not a single neuron? Why not two brains? Why not everything?

And then you get into all the usual problems of personal identity. Are you the same person over time? But the atoms in your body are changing. The form is changing. Whether you are the very atoms or the pattern in which they are arranged, this creates problems.

If what you actually are is this particular, arbitrary set of particles that currently composes your brain, then after a while, you become dispersed and might end up being split up over multiple bodies as other creatures eat the matter that once composed your body. And if you are these specific particles, realize that they were once separated and belonged to many different organisms. What are the odds that the collection that is you just happened to come together in one brain, all at the same time?

No, you couldn't simply be identical with this collection of atoms! What about the form, the pattern? If you are a particular pattern, consider that the form is constantly changing! You would only exist momentarily! There would be a succession of many, many separate selves, each living a moment in the course of a life.

That doesn't make sense either, does it? So what are you? Consider that you already accept, if you believe that you are a brain or a body, that what you are spans multiple things. It involves multiple particles, multiple cells, multiple organs, a span of time with many states, and so on. It is just that you think that what you are ends with your skull and your birth and death. But why would it end there? Is that some kind of magical boundary that encapsulates an ego? Does a skull boundary define an 'I'?

I think we tend to find it easy to accept that we are a brain, and to not notice that we are thinking that we are a multitude, because of the fact that, because of how our minds carve up the world into things, we think of the brain as one thing, like Ryle's pair of cows.

And then you can consider all the questions that arise with teleporters and the like. If we read all the information describing your body, destroying your body in the process, and then assemble a copy at a distant location, when the person steps out of the teleporter, is that person you? Do you, the same you that you are now, find yourself then on the other side? What if we make two copies? Which one will you be, if any? Or did you die?

How do you know that your form propagating from moment to moment isn't just like that teleporter? Is the experiencer of your perspective this moment the same one as an hour ago? I would say yes, obviously. Otherwise you couldn't experience the flow of time. Your identity must span time in order for you to experience change. And your identity must span some space and material in order for you to have a unified experience of all that your brain is doing, even to experience an apple as an apple, with its combination of color, shape, meaning, and so on, the processing of which involves many brain regions.

So you already have span, both temporal and spatial. You are already more than one thing and more than one state of those things. So why do you think that what you are is limited to this body and its lifespan?

Consider how the idea that you are simply that which is everything, that it is all one and you are it, would solve all of these problems in one fell swoop.

Why do you find yourself being Purple Pond? Well, being everyone and everything, you'd naturally expect to find yourself being Purple Pond. Consider the marble picking again. If you were allowed to hold all the marbles, should you be surprised to find yourself holding the golden one?

Think about it probabilistically. If you are in one of two scenarios, with you not knowing which, and you had to guess which one you are in, which should you bet on, the one in which your case is far from typical or the one in which your case is typical or even inevitable? For example, suppose we flip a coin and determine which of two prizes you get: A, all the marbles, including the golden one, or B, just one marble selected at random. Now suppose that before we tell you the result of the coin flip, we tell you that you definitely have the golden marble. Which should you expect to be true, that the coin chose A or B? You should guess A. In that case, having the golden marble is something you'd expect. In the other case, it would be a big surprise.

The fact that you find yourself being Purple Pond, being a brain at all, being alive at all, being in an inhabitable universe at all, and so on, is absolutely inevitable if you are everything, and astronomically unlikely if you are just one arbitrary three pound thing on a particular arbitrary planet, in a particular arbitrary galaxy, and so on.

Think about a lottery win. If you describe the situation objectively, it is not very surprising when someone wins. But if you find that you are the winner, that is a different thing, isn't it? That is surprising! But notice that it suddenly ceases to be surprising, even subjectively, if you happen to be everyone.

This idea even clears up all the confusion about the anthropic principle and the fine-tuning of the cosmos and whatnot. Why does the universe seem so fine-tuned? Suppose there is an infinite multiverse containing all possible universes. In one of them at least, these conditions will prevail. And if you are everywhere, naturally, you should expect to find yourself alive in a universe fine-tuned for life! But if you aren't everything, if you are just one arbitrary three pound hunk of matter, inexplicably having both span across a multiplicity of things and a limit to that span, then your situation is indeed unusual and suprising to find yourself in.

But there is a natural objection to all of this. Why don't you feel yourself being me and everyone else? Why don't you know that you are everyone? Why can't you access my memories?

There are some famous cases in which people with severe epilepsy have undergone a procedure in which the corpus callosum in their brain has been severed, effectively isolating the two hemispheres. If you aren't familiar with this, I'd suggest researching and reading about split-brain surgery. What results from this is a situation in which it seems that there are now two selves, one for each hemisphere. Using clever methods, you can ask one hemisphere a question and give it information while avoiding giving any information to the other. You quickly find that if you ask one hemisphere questions about what you have only shown the other hemisphere, the answers contain no information about it. You can show that there is no integration of information between the hemispheres. Further, the two hemispheres seem to have distinct desires, distinct plans for the future, and so on. And sometimes, one hand will try to button up a jacket while the other tries to keep it unbuttoned, and so on. Suddenly, it seems that there are two people in one skull, each controlling half the body.

What has happened here? Can your self, the very you that you are, be divided into two? If you undergo such a procedure, which of the hemispheres will you find yourself being afterwards?

Consider another hypothetical scenario. We take a guy named Bob, who is an amnesiac who cannot remember new information for longer than a few minutes, and we place him in a room with a chalkboard mounted on the wall. We show him things, give him experiences, and he records what he observes on the board. When we ask him what we have told him or what he has experienced, he consults the board. It basically serves as his memory. Now, suppose that we take him to a second room, room B, also with a board. But this board is blank. In this room, he does not have any access to what he wrote on the board in room A. We can replicate all the experiments from the split-brain studies using Bob in these two rooms, and we can show that there is no information integration between the rooms. In room B, Bob cannot give information about what he observed in room A, and vice versa. And he can't connect things observed in the two rooms.

Obviously, we can't conclude from this that there are two separate people here, one in room A and one in room B. Bob is one person regardless of the inability to integrate information between the rooms. The only issue here is that there is no way for information to pass from room A to room B and vice versa. While in room B, Bob knows nothing of his life in room A. He doesn't remember being in room A. He might have written a concerto in room A, but he would know nothing of it while in room B. If we give him a portable notebook, he might then integrate information between the two rooms, but without such a device, there is no reason to expect him to have access to information in the other room. The same goes for the two hemispheres in the split-brain. The corpus callosum is like a notebook allowing information to pass between hemispheres.

What's the point of this Bob business? I'd suggest that the very same situation holds for us as seemingly separate individuals. Our two brains are like the two rooms. There is one experiencer with both perspectives simultaneously, but over there, in your brain, there are obviously no memories from my brain. How would they get there? They'd have to get there by some local physical mechanism. In this brain over here, I lack access to what is stored in that brain over there. In the Oysteroid brain, I find no Purple Pond memories, naturally, and vice versa. And that's all there is to it. That's why we think we are distinct selves. In actuality, I believe, that which we are, that deepest inner witness that looks out from behind these eyes, is everywhere and is everything. And it isn't a separate self inhabiting the multiverse, as if there is one big soul assigned to one big multiverse. No! It is all just one whole. Your very self is the very substance of it all. The scenario with Bob isn't a perfect analogy here, as Bob is separate from the rooms.

There is one substance and it experiences all of its modifications and relations and is everywhere present to itself. And if you want to know what it is like to be it, just ask yourself. You're it. You're everything.

It isn't like reincarnation, where you can look forward to another life. No, you are living them all simultaneously and always. You are already over here, experiencing my life. You are already beyond the life of Purple Pond. You just can't access this information from there. While in that room, you don't know that you are also in this room and all the other rooms.

Take this seriously. Think about it. And realize that there is never again cause for envy. When you see someone else enjoying some life that you don't have, know that you have it, that you are that person. Also know that when you hurt another being, you are hurting yourself. It is none other than you that has the experience on the other side of whatever you do to another.

If you have made it to the end, thanks for giving all this your consideration!

Why am I the same person throughout my life?

There are several factors.

1. You have not forgotten 99.9% of your memories. Most of your mental functions are non-conscious; your memories are alive and well in this department. When you need a memory, non-conscious brain operations will provide it to you. (((Or not. Things do get forgotten, and there is always that business of not remembering who somebody is that you "you know you know" but you can't think of their name. All that stuff is normal.)))

2. While it is the case, as Heraclitus said, that you never step into the same river twice, the world is pretty stable for all practical purposes. You are part of the world, and you too remain pretty stable. If you de-stableize too much, you will be declared dead. Since you are posting here, you are probably still alive. Just guessing.

3. Some of the atoms in your brain are coming and going in fairly heavy traffic because you seem to be still alive. But just because there is trafficking of atoms and molecules in your brain doesn't mean that everything in there is being chewed up and lost. Your body does get renewed completely several times during your lifetime (with a few exceptions, one being a lot of those neurons inside your skull), but the shape of the structure stays the same.

I know I do feel like I'm the same person, but say that the many worlds interpretation of quantum mechanics is true, there will be an unimaginably huge amount of people who also think that they are me, does that mean all of them actually are? Does that mean that the woman who thinks she is a reincarnation of Marilyn Monroe actually is Marilyn Monroe? — A disturbed person

Forget about the many worlds of quantum mechanics. It's speculative and it isn't going to make any difference, anyway. It's not your problem.

The woman who thinks she is a reincarnation of Marilyn Monroe may enjoy thinking she is, and as long as she isn't annoying everyone by constantly trying to sing "Diamonds Are A Girl's Best Friend" or obsessing about her affair with President Kennedy, she's probably harmless.

4. Who else would you be?

I bet that whatever you feel, there is a lot of continuity in it. That is, you aren't constantly feeling like you have become somebody else, or are losing the continuity of identity that you had several days ago. Ideas sometimes occur to us that just aren't that helpful, and we waste time thinking about it. Like the many worlds business. There may be other universes, but as far as we know, we aren't going there.

So relax. Or get busy -- whatever is on your list of things to do.

Whether or not you’re the same person you were at an earlier time depends on how you mean the question. As I mention below, I think most would agree with me that you’re the same person as you were yesterday or last week, but not the same person you were a long time ago, in a much earlier distinctly-different part of your life.
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I would prefer not to rely on faith in the existence of a physical "soul" like described in many religions

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There’s no “Soul”, “Mind” or “Consciousness” separate from the body. The animal (including humans) is unitary. We’re the person, the animal, full-stop.
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, and I would also like to believe that the world around me is to some extent real.

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It’s real in the context of your life, and that’s real enough.
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Firstly, I understand that there is no argument or relevance for continuation of brain matter/brain atoms as the atoms in a brain are constantly being replaced all the time, and I don't see much significance in whether they are or not anyway.

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Yes, and an animal, including humans, is a system. There’s a story about a ship, in which one piece of the ship at a time is replaced, until eventually, years later, every part of the ship has been replaced, and the question is, is it the same ship as it was before the replacement process started? Sure, if the ship is regarded as a system.
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“This hatchet belonged to George Washington. Oh sure, it’s had a few new heads, and a few new handles.”
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But whether you’re the same person that you were at an earlier time depends on how you mean that question.
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There’s also a meaningful sense in which you aren’t the same person you were a long time ago. It’s plain to me that I’m not the same person that I was as a child, or even as a teenager. Of course I remember some of my concerns and priorities in those days, but I don’t know or understand how I justified those, though I suspect where I might have gotten some of them. It’s as if I know a few things about that person, as one might know about another person. I don’t even know the person that I was then.
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So I wouldn’t expect a definite, all-applicable, answer to that question. It depends on how you mean it.
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I’d say that (as I mentioned above) most would probably agree that you’re the same person as you were yesterday or last week, but not the same person that you were in a much earlier and distinctly different period of your life.
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I do accept that memory is important, but I have forgotten 99.9% of my memories and even the things that I do remember, I am not remembering in this very moment, if that makes sense.

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Yes, that’s like I was saying above.
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I know I do feel like I'm the same person, but say that the many worlds interpretation of quantum mechanics is true, there will be an unimaginably huge amount of people who also think that they are me, does that mean all of them actually are?

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Depends on how you mean it. They’re all the person with your name, but after a while they might differ significantly from you. You feel what you feel, not what they feel, and, in that meaningful sense, they aren’t you.
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Does that mean that the woman who thinks she is a reincarnation of Marilyn Monroe actually is Marilyn Monroe?

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No. I disagree with the notion that someone can remember a past life. In fact, I claim that the matter of whether or not a person has lived a past life is completely indeterminate.
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Maybe the way I perceive the world is fundamentally different to the way other people see the world - as in maybe the way I see/interpret colours is different from the way other people see them, but I do not have evidence for this and even if it is true, would it really be sufficient?

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I think a lot of people would agree with your impression of not being the same person you were a long time ago. I think you’re right.
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Michael Ossipoff

No one thread runs through the whole length of a rope.

Who else could you be?

To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day
To the last syllable of recorded time,
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.

When ropes are made out of continuously extruded fibers of nylon the threads or fibers could be as long as the rope.

Your statement is true of long ropes made out of hemp fibers, for instance, or linen, cotton, silk, etc.

Your statement is true of long ropes made out of hemp fibers, for instance, or linen, cotton, silk, etc. — Bitter Crank

True. It still makes an excellent metaphorical answer. One does not need anything to be the same now as it was then, in order to be the same person now as you were then.

A very pertinent question as far as I'm concerned. You have, what I call,a ONE problem. The concept of self/I is intricately associated with ONE. The letter "I" is ONE in Roman and Arabic numerals. Is this a coincidence? I don't know but it is central to the problem you are facing. We, instinctively(?), think that there can be only ONE self. We say "He's someONE" or that "noONE's in the room" and these linguistic terms indicate our deep-seated beliefs about identity.

However, some say that change is a truth that can't be denied. By that token we, every ONE of us, are always changing - mentally and physically. The self, then, must be gently detached from the number ONE and then reassigned to the ever-changing self. I am ONE but we are MANY.

Of course, and I got the metaphor. Sometimes I can't resist...

Nor I.

No one thread runs through the whole length of a rope. — Banno

We need to be very careful here. As I said in my reply to the OP and I'm quoting the evil demon from the movie Ghost Rider, ''I am one but we are many''. It is (was?) my belief that the self is not ONE but MANY and your rope analogy dovetails perfectly with what I said.

However, I think we need to look deeper into what we mean by ''different'' or ''change'' vis-a-vis our shared belief that there is no ONE thread that runs the length of the entire rope.

Consider the mental illness multiple personality disorder (MPD). The diagnosis is made only when two personalities are sufficiently different. Small differences in personality are common - so-called mood swings I believe - and these don't warrant the diagnosis of MPD.

Taking this line of thought further we see that much of the change (mental and physical) we notice in a person are diluted by the presence of at least one continuous, to use your words, thread.

The threads in a rope overlap in such a way that continuity (in other words self-identity) is maintained throughout. Most of us aren't diagnosed with MPD are we? Should we be? Or is your reasoning faulty?

Perhaps it's not the individual threads that is the self. Rather the entire rope is.

One rope or two?

One rope or two? — Banno

Depends on what you mean by ''rope''.

Exactly.

Exactly — Banno

So, redefining ''self'' will solve the conundrum? I guess my POV does suggest such a route but I also mean that there IS continuity in the timeline of a person -that the discontinuity alluded to by your analogy is irrelevant. Small changes can be ignored.

So, redefining ''self'' will solve the conundrum? — TheMadFool

Solve, or dissolve...

The point is that there need be nothing that ties you to who you once were.

The point is that there need be nothing that ties you to who you once were — Banno

(Y)
That speaks of some underlying objective i.e. wanting/hoping something to be the case, whatever that may be.

The point is that there need be nothing that ties you to who you once were — Banno

"All I know is that I know nothing" ?! :)

"All I know is that I know nothing" ?! :) — Vajk

"I"?

" " " "

You're not, we always change. Stuffs in our bodies are always dying

I know I do feel like I'm the same person, — A disturbed person

You cannot step into the same river twice. In fact you can't step into the same rive once.
What you feel when you feel 'the same person' is continuity of an ever changing reality.
You are not the same person as you were when you were five years old. You are not the same person you were yesterday. You were not even the same person you were when you stated to read this post.

I would prefer not to rely on faith in the existence of a physical "soul" like described in many religions, and I would also like to believe that the world around me is to some extent real. — A disturbed person

There is an "I", the Observer that is peering through the eyes and is learning, experimenting, creating, and evolving. This idea that we are some bouncing particles is a man-made myth and needs to be discarded in order to understand life. Actually, the Daoists had it right. The "I" resides in the center of the body and the brain along with the spine is more of a transmitter/receiver antenna.