My intuitive reaction to thought experiments such as described in the following question leaves me thinking I am not my body.

Almost Sure Mind Transfer via Parfit's Identity Theory (interesting thought experiment)

Here is a formalized argument representing my intuition. The two highlighted premises are argued in the answers below.

Premise 1) If the I is caused by the body, it is either caused by the body's matter and/or structure.

Premise 2) Given any two Is in a consciousness body's timeline, they are the same I.

Premise 3) If and only if two effects are the same, then the two causes must be the same.

Premise 4) Given two particular points in a body's timeline, the body's matter is completely different.

Conclusion 1) By premises 2-4 neither the body's matter, nor the matter/structure combination, can be the cause of the I.

Premise 5) It is possible to replicate the body's structure exactly. Yet the replica, despite having exactly the same structure, will have a different I.

Conclusion 2) By premises 2, 3 and 5 the body's dynamic structure cannot be the cause of the I.

Conclusion 3) By premise 1 and conclusions 1 and 2, the I is not caused by the body. In other words, I am not my body.

Is this argument deductively valid? Are any of the premises false? If none are false, is the argument sound?

If you disagree with premise 5, consider the alternative. For example, if someone could replicate your brain structure exactly on silicon, would you agree to be killed in the hopes you would be revived as an artificial intelligence? Or, say you were killed and your brain structure was instantiated twice in silicon. Which one will you be revived as?

Here are some related questions:

What is the modern solution to the mind-body problem for those who still hold the mind is separate?

If I upload my brain into a computer is it still me?

Would rebuilding a human body rebuild the person it was?

What's the difference between cloning and metabolism in terms of affecting personal identity?

  • Your mistake is to think that atoms and outside world really exist as you see them now. What you need and I (me the author of this post) need is to reflect on the infinite nature of THE most important human quality - imagination. Do you you think i can imagine your @yters world and you thinking about this question? Do you think in my imagination your body will be separate from your mind? Don't you think my(yours) imagination is one?
    – Asphir Dom
    May 13, 2014 at 23:58
  • Please research Leibniz and his geometric proofs that soul is immortal. It is very close to your ideas.
    – Asphir Dom
    May 14, 2014 at 0:02
  • I wasn't able to find Leibniz's proof after some googling. Please post a link if you have one handy.
    – yters
    May 14, 2014 at 3:16
  • Related question: philosophy.stackexchange.com/questions/2432/…
    – yters
    May 15, 2014 at 5:59
  • 1
    Your premise 3 is at odds with quantum mechanics. Or in more classical terms: Both the effect of the coin falling on heads, and the effect of the coin falling on tails can be an effect of the same cause, tossing the coin. Indeed, if that were not so, then tossing a coin would be pointless.
    – celtschk
    May 17, 2014 at 10:19

10 Answers 10


Identical twins are clones of each other that started off in an identical state (as they both result from the division of a fertilized egg). Identical twins do not consider themselves as being a single "I", but instead have two distinct identities. The reason for this is that their sense of self is to a large extent the result of observing a correlation between their own intentions and the actions of their bodies, and a lack of correlation between their intentions and the actions of the bodies of others. The sense of "I" is to a large extent a result of neuro-biology and development. Your clone would not be the same "I", just an equivalent "I".

Were you to clone yourself (say via a transporter malfunction), you and your clones would immediately realise that you were different people, even though your brain states were identical at the point of duplication, because your body would follow your intentions and not your clones and vice versa. The fact that you can't both be in the same physical place at the same time means there symmetry is broken, so at some point your behaviours will diverge.

Our sense of "I" is very much about our body, but it is a bit like the old joke about the chap who owned a cricket bat that used to belong to WG Grace, of course it has had a new blade and three new handles since then... The point being that if you carry on using the bat, to you it still seems the same cricket bat, even though none of the parts are original, it is still perceived as continuous.

Update: The original question was

"Let's assume my body is cloned into two other bodies, and my current body is destroyed. This all happens simultaneously, so there is no break in chronological continuity. The exact same "I" in the original body, if it is caused by the body, would show up in both clones. However, I can only ever be conscious of being in one of the two."

The error here is assuming that the original "I" still exists, if it doesn't, that "I" can't be conscious of being in either of the two. The two clones contain copies of the original "I", but a copy is not the original; they will perceive themselves as distinct entities because they are in distinct bodies.

  • Right, this is exactly my point. Since they are not the same "I" but the bodies start from the same state, the "I" is not reducible to the body state. Therefore, the "I" comes from some non-bodily source.
    – yters
    May 2, 2014 at 16:01
  • No, it is the difference in body state that gives rise to the sense of "I". In the case of the transporter clones, they both inhabit bodies in different states (positions in space and or time) which means they would immediately recognize each other as separate entities. The sense of "I" develops as a result of our interactions with our environment. Our plasticity in this respect is why immersive virtual reality is effective. There is no need for a non-bodily source to explain this, but without demonstrating that one doesn't exist. May 2, 2014 at 17:25
  • 2
    Being in different positions in space will result in differences in perception, which in turn give a difference in body (brain) state. May 2, 2014 at 17:45
  • 2
    but as I have pointed out two distinct physical bodies cannot be in identical state simply because they are distinct. May 2, 2014 at 18:59
  • 2
    as I said in my answer, we are not aware of the replacement of parts of our bodies because the use is continuous. However in the case of the transporter clones it isn't, because they have abruptly awoken in a new, distinct body. May 3, 2014 at 17:51

I don't think the thought experiment proves what you think it proves. We'll work primarily from this section:

The exact same "I" in the original body, if it is caused by the body, would show up in both clones. However, I can only ever be conscious of being in one of the two.

There are several problematic phrases:

  1. The exact same "I"
  2. caused by the body
  3. caused by the body
  4. I can only ever be conscious of being in one of the two.
  5. I can only ever be conscious of being in one of the two.
  6. I can only ever be conscious of being in one of the two.

Starting with (1), there are many different ways of being the same. I'm the same matter if you vaporize me into a pile of atoms. I'm the same person even as my matter changes. I've got the same hair as someone else. If you want to say exact same, then that would mean same in every respect. But one of these respects is that I am numerically identical with myself. The term numerical identity is confusing, but it basically means that there's a me you can point to. It's impossible that your clones are instantaneously so with you. At best one of them is (and then one would not be a clone).

Moving to (2), there's a few different ideas that could get parsed as caused by a body. First, do you mean matter by itself is the cause? if so, that's pretty hard to imagine. Second, do you mean the body as a organized system causes the I. If so, it's probably better to think of this as soul or form (following Aristotle, Aquinas, and many others). If the second description, then the suggested conclusion fails, because identity follows from having the same self organizing the bodily matter.

Moving to (3), I take it the "the" means "this", i.e. my I is caused by having a particular body. but if so, then there's no you left if that body is gone.

Moving to (4), who is this I? What ensures this is the same I? Is it the same because it would respond to things in its world in the same way? Because it has an identical brain state? This is not at all clear, and without that clarity it's not at all obvious that it makes sense to speak of an I after what was the I or at least the body housing the I is gone.

(5) seems to identify the I with consciousness -- not the body.

(6) The issue in 6 is that you've now defined being an I as being conscious of having a body and knowing it is yours. It's not at all clear this is what being an I is or that consciousness requires this or that this is sufficient for consciousness.

  • The "I" being described is a self conscious first person perspective of the world. If the "I" is caused by an organized system in your #2, then the same organized system will cause the same "I". How is one organized system identical to another? It is the structure, since the matter can completely change and the "I" stays the same. In the case of the clones, the structure is completely the same, so the same self conscious "I" should result. However, if two consciousnesses are the same, then they are conscious of the same thing, which is impossible in the case of the clones.
    – yters
    May 3, 2014 at 18:07
  • Therefore, since the exact same organizing system does not cause the exact same "I", the "I" is not reducible to the organizing system nor its matter (the body). And that gives the conclusion that whatever the "I" is, it is not reducible to and is not caused by the body. Which also implies that destroying the body doesn't necessarily destroy the "I".
    – yters
    May 3, 2014 at 18:13

One crucial perspective on this problem holds that our sense of identity is itself an illusion. All the way back in the seventeenth century, John Locke was thinking of exactly the same questions. ("Clones" notwithstanding, this is a very old problem.)

Consciousness and Identity in Locke

Locke explicitly holds that personal identity is determined by consciousness alone (see here for the source):

As far as any intelligent being can repeat the idea of any past action with the same consciousness it had of it at first, and with the same consciousness it has of any present action; so far it is the same personal self. For it is by the consciousness it has of its present thoughts and actions, that it is self to itself now, and so will be the same self, as far as the same consciousness can extend to actions past or to come, and would be by distance of time, or change of substance, no more two persons, than a man be two men by wearing other clothes to-day than he did yesterday, with a long or a short sleep between.

This helps us deal with knotty situations in which consciousness moves between bodies:

Could we suppose two distinct incommunicable consciousnesses acting the same body, the one constantly by day, the other by night; and, on the other side, the same consciousness, acting by intervals, two distinct bodies: I ask, in the first case, whether the day and the night — man would not be two as distinct persons as Socrates and Plato? And whether, in the second case, there would not be one person in two distinct bodies, as much as one man is the same in two distinct clothings?

So it's possible for one body to house two separate consciousnesses, and they would not be the same person. And it's also possible for two bodies to house the same consciousness, in which case the same person would exist in two different bodies. Locke doesn't consider the simultaneous case, but the conclusions he draws apply here as well; as long as the consciousness is the same, the person is the same, but as soon as the consciousness diverges (after the cloning process), the person is different.

Discontinuity and the Fictional Self

However, another thing that Locke doesn't explore is the possibility that one might be mistaken about one's memory of the past. This is because our experience is not perfectly continuous. Locke's example of the same body housing two different consciousnesses by day (Socrates) and by night (Plato) is instructive here; Socrates doesn't know a thing about Plato's activities. He might not even know the Plato exists! But this is a problem, because it shows that we have no particular reason to suppose that our consciousness is really the same before and after we lose it in sleep. The discontinuity that allows Plato to invade Socrates' body without Socrates knowing it also makes the internal identity of Socrates less certain.

This is why David Hume, writing a few decades later, insisted that the very notion of identity -- of the "self" -- is a fiction. Our experience is inescapably fragmentary, and any attempt to impose order and continuity on our fragmentary experience tells a lie about that experience.

So the problem with the cloning scenario you describe (from this point of view) is not that we have two bodies with the same consciousness; it's that we're imagining consciousness as ever being "the same" at all. If identity is always an illusion, then the cloning scenario you describe no longer causes any particular difficulties; we can hold multiple fictions of identity in mind at the same time, because they're all essentially false!

  • Assume for sake of argument that our perception of consciousness is not an illusion.
    – yters
    May 3, 2014 at 15:23
  • @yters, I am! I never said that our perception of consciousness is an illusion. Our perception of consciousness is perfectly real. It's just irreducibly fragmentary -- it properly has no "identity." (According to Hume, that is.)
    – senderle
    May 3, 2014 at 15:35
  • If we perceive consciousness as unified, but it is in fact not, then you are saying it is an illusion. We are perceiving something to be true which is in fact false.
    – yters
    May 4, 2014 at 18:19
  • @yters, I'm saying we don't actually perceive consciousness as unified. We sleep, and we don't mistakenly believe that we haven't slept. We experience other kinds of discontinuities in our consciousness as well. I don't think this is a matter of debate; if you disagree, then I'll let Hume speak for me: "If any one, upon serious and unprejudiced reflection thinks he has a different notion of himself, I must confess I can reason no longer with him."
    – senderle
    May 4, 2014 at 18:29
  • 2
    @yters, you've acknowledged that there are gaps in our consciousness, so we don't have to agree to disagree. Remember that I'm not the one making this claim. I'm just trying to accurately describe Hume's argument. For Hume, identity just is continuity of perception. Without continuity of perception, there is no identity. They're the same thing. So you can see that he would reject the claim that you perceive the same I before and after you go to sleep, because it directly contradicts his definition of "same." You are, of course, free to reject his definition, but he has reasons for it.
    – senderle
    May 5, 2014 at 1:57

It just shows that after this thought experiment, there would be two of you, one in each of the two bodies.

In particular, clone A will respond as you would if you were in clone A's place, as will clone B. But A and B do not have the same place.

  • You misunderstand the thought experiment.
    – yters
    May 4, 2014 at 18:20
  • @yters - I'm just rejecting the premises that are especially problematic for any theory of knowledge, e.g. 3 (unless it's conditional on the "must", in which case it's so weak it doesn't say anything relevant because its premise is not met). (4 is empirically wrong also.) You're left with the situation I describe.
    – Rex Kerr
    Oct 8, 2015 at 15:28

It's more interesting to consider the case of making two cloned copies. They each start with the same exact state, identical to you; but from that moment on, they're independent. They each have an I.

Now, so do you. If you're then killed, you're dead. Two new I's come into existence; each initially feeling and thinking exactly as you at the moment of cloning; and for every moment thereafter, a separate human being. An I. A subjective consciousness.

As it happens we have a real world model in common use. In computer programming, a process is a thread of control with its own private memory space. Typically a process is a running program, such as a copy of your browser or an instance of a word processing program

Now, a process can create another subprocess. (In Unix-like systems this is called a fork, but other operating systems have analagous constructs.)

At the moment of forking the subprocess inherits the entire memory space of the parent process. At that moment, these are two separate processes, or running programs, executing in that machine. They have the exact same state at that moment. But from the moment of cloning and onward, these are two separate processes. They are totally independent of each other (except for the relationship of "is the parent of" that the OS remembers).

No programmer would ever think they're "the same process." They're two separate processes ... independent software entities running under the operating system.

They do happen to

a) Run the exact same code. They execute the same program. They have the same code.

b) The subprocess is initialized to have the exact same state as the parent process at the moment of cloning.

It seems to me that the field of computer programming already has a rich metaphor for the notion of cloning.

A cloned human is a new human that runs the same code (DNA and basic brain wiring) and initially has its state set equal to the state of the parent human. From that moment on, the two humans function independently, have different life experiences, develop their separate minds independently, act independently in the world. Exactly like a parent and child process in a Unix-like operating system.

And for that matter, exactly the way a human makes a new child now! You spawn a new human and initialize it to a new-born infant state. Everyone instinctively understand that the baby is a new human being. Likewise if you cloned yourself, your clone would be at that moment a brand new human being; just one whose initial state was set equal to your current state. But it's a different I. And if they kill you, you're dead. It's your clone who will live.

This is conceptually no different than a human giving birth. It's merely a question of setting the initial state. [For that matter, why not clone me but make me a lot younger!! There would be a market for that :-)]

Now, how strong is my analogy between operating system process cloning and human mind-cloning or Star Trek transporter technology?

As a metaphor it's solid. I think it provides great clarity when thinking about what it would mean to transfer a human consciousness into a different substrate.

Whether it's literally true in some way ... we have no way of knowing. The science of consciousness (the "hard problem," as they say) is a tough nut to crack. We shouldn't be deluded by the fact that we have cool computer technology, into thinking that we'll soon be uploading minds.

We don't even know what a mind is.

  • 3
    But a child process has internal access to knowledge that distinguishes it from the parent -- and that knowledge is often important! That seems different from what the OP is suggesting. The clones may have external but may not have internal knowledge that they are clones.
    – senderle
    May 3, 2014 at 14:10

The majority of this question and other answers seem to be concerned with definitions of terminology (such as "I") and labeling/classifying things (such as, do X and Y fall into the same 'identity' or not).

Let's instead focus on science as a means of getting observable predictions about the behavior of reality. What should we expect to see if "Let's assume my body is cloned into two other bodies, and my current body is destroyed." somehow is implemented?

Would both bodies claim to be 'yters' (the OP user)? Yes, they would - their uninterrupted conciousness knows their name, and they'd both have memories of always being 'yters'.

Would both bodies claim to be 'the original yters'? Yes, they would - from their perspective, they've always been the original yters but suddenly a unique, distinct, separate clone appeared that also claims to be 'yters'.

Would the bodies have a psychological identity crisis? Experience shows that it's likely.

Would friends and relatives be able to distinguish one of the clones from the original? No, if the physical process is sufficiently good and doesn't leave identifying marks.

Would friends and relatives be able to distinguish one of the clones from the other? Not initially, but in time, yes, as they'd accumulate different experiences, memories and skills, and slowly become more like identical twins that share most of early memories.

But questions such as "Is 'yters' alive?", "what a mind is exactly?" are a bit meaningless in the sense that you can have wildly different answers that give the exact same predictions about future reality, so those answers are not distinguishable in practice - we could write any arbitrary one of the options down to use in law&legal process (just as we do for many current things) where such nuances matter; but none of those interpretations are "right" as in predicting different future reality than "wrong" interpretations.

The definition, location and behavior of mind and consciousness would matter a lot in building a practical implementation of such a cloning process, and the sideffect risks of imperfect copying; but IF such a perfect copy is implemented, then it doesn't matter how it's implemented as the results are the same.

  • Your response doesn't address my question at all.
    – yters
    May 4, 2014 at 18:21
  • 2
    @yters This response is that major parts of your question rely on a very particular definition of "I" and disappear/become meaningless for other possible definitions of "I"; and that it'd be more productive to discuss the thought experiment as such, instead of arguing about that definition. E.g. "However, I can only ever be conscious of being in one of the two" is a bit shaky statement - it's literally true, but if there are two copies of "I", then each of two bodies has a "you" that's conscious of being inside, and that copy of you is inside only one of them.
    – Peteris
    May 5, 2014 at 13:11
  • Similarly, "since both clones start out with exactly the same state, the consciousness should be unified" would need some argumentation on why you think that it would it be unified in any way, instead of simply diverging from that initial identical state.
    – Peteris
    May 5, 2014 at 13:12

Premise 4 is false: the body's matter is not completely different from one time to the next.

Over reasonable timescales, say up to hours or days, and at spatial scales larger than say the size of tissue cells, The physical configuration of our bodies is largely conserved. There are some small scale short time changes, but Theseus wouldn't complain if you replace a few nails in his ship. Over longer time scales, yes there are macroscopic changes, but the I of today is not the same I that I was 10 years ago (though current me has spatial-temporal continuity with the earlier one).

The key assumption here is that the identification of "I" over time doesn't depend on the molecular level configuration details, just like with every other macroscopic object.


I'd say I'm both of my clones, where a clone is a complete duplicate at a subatomic level. I'd also be a completely accurate virtual simulation of any of them.

The question is biased, and the conclusions you derive from this biased axiom are simply wrong. I consider I am the information (includes personality) stored in my brain, therefore any complete copy of my brain (in any format or substrate) is me. You seem to have a somewhat mystical notion of "I" where the soul or essence is lost in the process of duplication of the body.

That is nonsense, lesions in the brain have shown clear impact on the behaviour, cognitive capabilities and personality of the people that have suffered them. Without a physical existence we would need to ask ourselves what kind of existence do we have, and that only leads to nonsense.

If I get to be cloned (duplicated) twice, then the information in the brains will diverge, I'll get to live two lives. That's great. Those two people will have been the same person in the moment of the duplication, but they would be different (maybe not a lot) after some time, you could say they are different persons or different versions of the same person. that's semantics.

We all should try to be the best possible version of ourselves.

  • 1
    You say "any complete copy of my brain (in any format or substrate) is me." But that's exactly what I took the OP to be saying. I don't see that you've actually disagreed with the OP at all here.
    – senderle
    May 3, 2014 at 14:16
  • @senderle that's interesting because the OP seems to be saying exactly the opposite to me.
    – Trylks
    May 5, 2014 at 9:39
  • Yes, it is interesting, and perhaps there's an insight buried here; or at least some clarification is in order. What exactly do you disagree with? Your claim that the OP has "a somewhat mystical notion of 'I' where the soul or essence is lost in the process of duplication of the body" doesn't fit with anything I see in the question as currently stated. Where does it talk about "loss"? Perhaps you see something I don't? Could you quote the lines you disagree with?
    – senderle
    May 5, 2014 at 15:03
  • @senderle «The exact same "I" in the original body, if it is caused by the body, would show up in both clones. However, I can only ever be conscious of being in one of the two.» Implicit reasoning: «Therefore "I"'m not in the two bodies, therefore the "I" is not caused by the body.» Explicit conclussion: «Therefore, my consciousness is not a product of my body's state.» The problem is the assumption: «I can only ever be conscious of being in one of the two.» You are conscious of being in the two, separately.
    – Trylks
    May 6, 2014 at 9:47
  • But again, it looks to me like "you are conscious of being in the two, separately" says the same thing, because of that word "separately." This thought experiment makes it look as though "I" am simultaneously one and two people. That's exactly the problem. You may draw a different conclusion from the problem than yters does, but I can't yet tell what that conclusion is or how it differs.
    – senderle
    May 6, 2014 at 13:49

Regarding premise 1, there are differing definitions of what "matter" is. The science of physics deals with some things which are not matter such as photons.

I disagree with premise 2. Much of what "I" meant at some point in time does not exist any more. And by the way, newborns do not appear to even have a "I". But this probably depends on how you define "I".

Premise 3 is obviously false. Consider 2+2 and 1+3: two different causes, same effect. Possibly what you meant is different from what you wrote. In case you meant that the same causes produce the same effects, this true at our level of perception and false at the quantum level. Are quantum physics relevant to what "I" is? I do not know. Would you rule this out? If so, why?

Premise 5 seems very dubious.

Regarding your alternative to 5, most human beings would not agree to get killed no matter what. I do not think this proves anything relevant here. Human behaviour cannot be reduced to rationality.


I think some of the challenge is that you assume a priori that the timeline for a body is well defined. Consider the case of pregnancy (always a challenge case with these sorts of things) by premise 2, "Given any two Is in a consciousness body's timeline, they are the same I." the baby has no "I" until the moment it has its own body. But the cells are simply those of the body of the mother (and a little material from the father), so they are arguably part of the mother at first. There's a discontinuity there. There's also a discontinuity at death for the same reason. The body continues for quite some time after death (as a corpse). This leads to an interesting complication with the silicon argument. Consider that you are the first "I" in a particular silicon body. At some point you die, and the silicon is re-uploaded with a "new" "I," but it cannot possibly be a new "I" because the silicon body's timeline is still going.

Another thing to consider is the case of conjoined twins. Most appear to have one body with two consciousnesses, but there are records of conjoined twins with a link between their brains which lead to questions of whether they are one consciousness or two.

Also worth looking at is a slow continuous cloning process, which invokes some Ship of Theseus style questions. Rather than a nice easy instantaneous "here's your clone," allow the clone to not only grow over time, but as its consciousness grows to be a mirror of yours, you can use the body as your own. Think of it like your body just getting "bigger." Then, at some point, you begin drawing a barrier between the two bodies (perhaps shutting down a high speed data link). It is well recognized that individuals of a skilled trade often develop a sense that the tool is "part of themselves," so it seems reasonable you might find this second body to be "part of yourself." If, later, it is clearly cut off from your influence, but exhibits conscious behavior, is it still "part of yourself?" At what point did it develop a new "I?"

All of these challenges have two things in common: abuse of the discontinuity at the creation of an "I" and destruction of an "I," and the premise that "I"s are exclusive within some bounded system (like a body). All of these challenges are uncomfortable corner cases where those nice crisp discontinuities get muddled by continuous changes.

As a general rule, any theory of "I" with discontinuities at birth and death will develop idiosyncrasies if it attempts to define all of its thought experiments using scientifically achievable procedures on the body. It is currently believed by science that the world is continuous and differentiable. If one assumes a discontinuity in level of meaning of "I," one finds there must always be at least one uncomfortable case where a virtually indistinguishable shift in body "causes" an "I" to appear or not. (If you want to see just how much discomfort it can cause, consider trying to make sense of all of the opinions on abortion at the same time. The concept of when a life starts has wracked the US for years, trying to fit a discontinuity onto a physical process)

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