1) During a deep sleep, your consciousness deactivates to reactivate upon awakening

2) During a deep sleep, you are narcotized and killed, to be replaced instantly by an identical copy, which wakes with an identical consciousness

3) During a deep sleep, you are narcotized and killed. On a very distant planet, there was already an identical copy of you, which wakes up normally.

From the subjective point of view, what changes?

From a subjective point of view, these three cases are identical, your consciousness continues smoothly. Whatever the "place" where it awakens, it will be perceived as a continuous flow, interrupted just by the night break. Every time you wake up it is not possible to know with certainty if you are in the situation described by 1, 2 or 3. Metaphorically, one could consider consciousness as a musical file reproduced by any apparatus: if the reproduction ceases and starts again in an identical medium, it is the place and material of the apparatus that changes, not the music. Likewise, if my experience is part of consciousness and it continues identically elsewhere, what changes is the place of consciousness, not the experience.

(Inspired by a mental experiment by Derek Parfit, in Reasons and Persons)

  • 1
    How would two copies of me ever have the same consciousness? Clearly, if they were alive at the same time, they would have two different consciousnesses. Arranging it so that one lives after the other changes nothing -- they continue to have two different consciousnesses. To say what you are saying, you would need to define consciousness in terms of something other than the continuity of experience. So, what would that new definition be?
    – user9166
    Commented Aug 2, 2018 at 20:53
  • I disagree: arranging so that one lives after the other does matter, if we accept that we don't die every time we take a nap. Case 1 and 2 are the same for the conscience. What's the difference for the continuity of experience if after a pause it pop up in a clone or in the old body? Commented Aug 2, 2018 at 21:24
  • Our experience is not discontinuous when we nap. We dream, we respond to surrounding conditions like noise or changes in temperature, etc. We may not remember this stuff, but we do it. I may not remember driving home yesterday, but that does not mean I had no consciousness when doing it. You have conflated ongoing experience with consciousness, and I don't accept that they are the same thing. People with complete amnesia, who cannot form new memories have no cumulative, ongoing experience, but they do have consciousness. They can find something funny, make a bed, or adjust the thermostat..
    – user9166
    Commented Aug 2, 2018 at 21:39
  • I'm talking about "conscious experience", not bodily changes in general, and it pauses during sleep. People with amnesia have experiences, their short term memory works, they are not p-zombie. Moreover: "[...] says Michael Perlis, the director of the Behavioral Sleep Medicine program at the University of Pennsylvania. “Stage 4 sleep is not far removed from coma or brain death. While recuperative and restorative, it’s not something you’d want to overdose on.” from nationalgeographic.com/magazine/2018/08/science-of-sleep Commented Aug 2, 2018 at 21:42
  • Fine. no input is welcome. I will go away. But this still makes no sense. If there were two of me, at the same time or different times, they would have different continuous consciousness, not the same one. That consciousness reduces to a minimum does not mean it stops. And we are not talking about the same form of amnesia. There are diseases that prevent the formation of new short-term memories, they lead first to confabulation disorders and ultimately to simply living in continuous reaction.
    – user9166
    Commented Aug 2, 2018 at 21:52

7 Answers 7


So far I like @jobermark's answer the best, but there's a missing aspect here; your question has a hidden premise. Let's review:

1) During a deep sleep, your consciousness deactivates to reactivate upon awakening
2) During a deep sleep, you are narcotized and killed, to be replaced instantly by an identical copy, which wakes with your own consciousness
3) During a deep sleep, you are narcotized and killed. On a very distant planet, there was already an identical copy of you, which wakes up normally.

In (1), we can easily talk about the constancy of the body. I could dwell on this but to highlight what I mean let's just proceed.

In (2) you start with the hidden premise: "which wakes with your own consciousness". The premise is that consciousness is a "thing" that has a unique identity. In other words, it's not just consciousness that the identical copy wakes up with in this scenario, it's something you're calling "your" consciousness. Distance here doesn't quite matter, so (3) has the same problem, only you moved it to another planet.

To highlight this premise let's present one more scenario:
4) During a deep sleep, your consciousness deactivates and reactivates upon awakening. But before you wake up, you're moved 6 feet over, and an identical copy of you is put where you were sleeping. Meanwhile, on a very distant planet, there was already an identical copy of you, which wakes up normally.

Nobody was harmed in this scenario; three people just woke up. Somehow, which we'll ignore, they are "synchronized" to be identical copies. Presumably there's a problem of which one is you; all three remember going to sleep just prior to your nap (since presumably memory is stored in a state in your body, and all are identical). But only one of these can be the real you. Right?

Not necessarily. We need not even entertain that all three individuals share the same conscious; indeed, I would presume they don't. But all three do share the remembered experience of going to sleep. I'm specifically questioning the hidden premise, which is that there's some "law" by which if there's one you in the past, there must be at most one in the present; that there's at most one "genuine" you.

From this perspective, in scenario 4, there could be three you's. One wakes up in the same spot. One in the same body. Another mysteriously finds himself on a strange planet. None are the same as each other; all are the same as the guy who went to sleep. "The real you" simply isn't a thing; there are just conscious beings that have the capacity of remembering the experience of being a particular prior conscious being. Maybe we can postulate that this is wrong... that there's some genuine you that gets carried over... so, postulate it. Give some ideas of what it means and when it applies, and you may or may not solve your own problem.

But one thing's for sure. The hidden premise being exposed, you would have to postulate it if you want to consider it. You can't simply presume it.

  • I completely agree, I should modify (2) my mistake, sorry. So, 2) During a deep sleep, you are narcotized and killed, to be replaced instantly by an identical copy, which wakes with an identical consciousness". If you like, you can edit my question, or I'll do it. But the question remains: is that identical consciousness the same who went to sleep the night before? About your interesting (4) scenario, it's not a problem to suppose that these are three different (albeit very similar) consciousness, since from the very moment they wake up there will be some difference in their experience. Commented Aug 4, 2018 at 20:08
  • @FrancescoD'Isa What "the same" means needs to be defined. One of the most visceral things about self identity is the uniqueness of perspective; I see what I see and you don't, you see what you see and I don't. Analogously, I remember seeing what I saw in the past, not what you did, and vice versa. This is a perfectly fine definition of sameness; applying it here, woke-up-in-same spot guy, woke-up-in-same-body guy, and woke-up-on-planet-x guy are all the same as went-to-sleep guy, but not the same as each other...
    – H Walters
    Commented Aug 4, 2018 at 22:42
  • ...unless you have a different definition of same, this does indeed answer your question. Same-ness here isn't a transitive property.
    – H Walters
    Commented Aug 4, 2018 at 22:43
  • woke-up-in-same spot guy, woke-up-in-same-body guy, and woke-up-on-planet-x guy are all the same as went-to-sleep guy, but when they wake up they have immediately different experiences: they see different things etc. Commented Aug 5, 2018 at 5:53

1) During a deep sleep, your consciousness deactivates to reactivate upon awakening

What is this consiousness thing?

You seem to be modeling it as software run on the hardware of the nervous system.   Is a reactivate instance of software the same 'thing' as a deactivated one just because it is spawned from the same memory backup and run on the same hardware archetecture? Or is continuity of consciousness an illusion?

2) During a deep sleep, you are narcotized and killed, to be replaced instantly by an identical copy, which wakes with your own consciousness

Whatever this consciousness thing is, the new body clearly wakes up with its own copy of it.

In what sense is a new instance of software spawned by a backup of data run on new (albiet identical) hardware considered the same thing?

3) During a deep sleep, you are narcotized and killed. On a very distant planet, there was already an identical copy of you, which wakes up normally.

Are you postulating that this already existing copy was somehow unable to activate conciousness until you were killed?

What aspect of this consciousness thing suggests that an individual's liscenced copy can be run on exactly one hardware system at a time? Or that decomishioning one system would automatically enable the alternate hardware to operate?

What about: 4) During a deep sleep, an identical copy of you is placed beside you, and you both wake up normally.

Which body has your consciousness? The one which wakes first? Both? Neither?


From the outside perspective, there's no way to tell the difference.

From the perspective of the copy, there's no way to tell the difference.

From the perspective of the original, they will never know, as their consciousness has ceased. Whether or not a copy has been made is irrelevant.

Perform the experiment with both conscious and it will demonstrate the issue.

If you have two identical bodies, Body A and Body B, both conscious, they will experience the world separately and interact independently - it will not be one consciousness using two bodies at once. If they're in the same room, they'll be looking at each other, not knowing what the other is thinking.

If you then shoot Body A, that consciousness is gone. Whether or not Body A is awake is also irrelevant. In effect, for Body A, nothing about Body B matters, they still experience the world in the same way.

  • Thank you for your comment. Anyway, the question is: what happens from the perspective of the subjective consciousness? Of what you call "I" in this case? I agree that with two different bodies it's like you say, they have two different consciences. (the original teleport thought-experiment by Derik Parfit has many similarities to your proposal) Commented Aug 2, 2018 at 20:46
  • Apologies, maybe I'm misunderstanding what you're calling "I" in this case, could you clarify? I was considering there two be two "I"s, the copy and the original. As soon as you make a copy, there are two consciousnesses, not one, even if individually they wouldn't know anything had happened as noted in the answer.
    – Elle H
    Commented Aug 2, 2018 at 20:51
  • Excuse me if I wasn't clear: I'd say the subjective experience of the self. That thing you think is going on after a night's sleep. Both in a standard case (1) and non-standard case (2,3), it stops and restarts. Does it really matter where? (Of course, if there are still two clones, it does matter) Commented Aug 2, 2018 at 20:56

Sorry, this is long and winding and ultimately goes nowhere, because it is a deconstruction and not an argument. But I think the perspective is useful.

First, the detail of deep sleep is irrelevant:

If while sleeping I adjust my covers in the middle of the night because I am cold, I am applying logic, I am reacting to a sensation -- I am conscious. I have no ongoing memory stream to go along with that consciousness, but I am not simply making autonomic bodily motions like breathing or reflexive responses like moving away from a touch. My behavior is purposeful and involves both awareness and deduction, if on a rather minimal level. So the argument that consciousness ceases in sleep is unconvincing. Consciousness may reduce to an arbitrarily low level, but there is no proof it ever ceases. Arguments from the 'fact' that we are unconscious during sleep are therefore not really proven.

Second, all the details of timing are irrelevant:

If consciousness inheres in a memory stream then when two copies that proceed from the same memory stream exist, they either share consciousness, or they do not. So if I made a copy of myself, without destroying the original, would that copy share my consciousness, or not? Our instinct is no. The two copies would have separate wills, and could make differing decisions as soon as both existed. If the will is not unified, it is hard to see that will as belonging to an individual. So there are multiple individuals, and multiple consciousnesses.

So if we make a copy, and we consider the consciousness of the copy, how can it matter whether the original is destroyed? For it to matter would be a strange sort of change at a distance without any contact or connection. Consider this in a sort of 'Schroedinger's cat' scenario, where the original is isolated from us at the moment the copy comes into being. If the original were destroyed at just the right time, we would have to say this copy's consciousness was a continuation of the original's and if it were destroyed a single second later, we would have to decide otherwise. Since it is possible for us to not even know, I don't see how we can consider this a form of logic. It is really only an analogy. There is simply an arbitrary choice of labels, and labeling is not an aspect of consciousness. What we see continuing is identity from a third-party point of view, and not consciousness.

In that case, that continuity is the same whether there is only one of me at a time or whether you multiply me. And the prior logic suggests that it is not the same consciousness if you do multiply me. So this is not the same consciousness.

Finally, the concept of continuity is irrelevant:

If I awaken, as the copy, my behavior is a continuation of the memory stream of the original. If I awaken as the original, my behavior is a continuation of the memory stream of the original. If I as the original am killed and reconstituted centuries later, and two dozen copies are made, each of them has behavior that is a continuation of the memory stream of the original. But these will be a second consciousness, or maybe a single consciousness or a dozen consciousnesses. So why do we care about continuity of consciousness?

We don't.

Daniel Dennett's argument is that consciousness is an orienting signal that sits ready to adapt to updates in the memory stream. The timeline of experience is awareness of the changes in our composite mental state as we try to choose the next memory to consider conscious. But we can be conscious of a memory that is seconds old or one that is decades old before we return to the state of seeking a next conscious focus. So consciousness is in fact always of the past, and is indistinguishable from memory itself.

In that case, consciousness of the current moment is impossible. The feeling of it is an epiphenomenon, not a reality, and that is why it is basically impossible to argue about it logically. You can continually choose as your current memory the sensation of being focused on the temporal stream in the last focal period, but by the time you can choose it, even that is a memory of an event in the past.

If 'now' is not a thing, consciousness itself is not continuous from instant to instant, and it does not have or need a timeline. Nor can providing it a timeline unify or distinguish between 'instances of consciousness'. This whole line of reasoning within the philosophy of mind needs a different orientation and a different vocabulary.

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    – Philip Klöcking
    Commented Aug 3, 2018 at 17:24

Hindu philosophy asserts that there are four states of consciousness, the first three being the waking, dream, and dreamless states. The fourth state is the realm of the superconsciousness, nirvana, the turiya (which simply means the fourth). This is expounded in the Mandukya Upanishad. It is the shortest of the major Upanishads, being only 12 verses in length. Nevertheless, it has been commented on in detail by Gaudapada, the guru of the guru of Sankaracharya. Both the Mandukya with Sankaracharya's commentary and Gaudapada's commentary (called the Karika) are available here - https://www.wisdomlib.org/hinduism/book/mandukya-upanishad-karika-bhashya. Gaudapada's commentary is considered by many to be one of the cornerstone commentaries of modern Advaita philosophy.

The dreamless state you are referring to is referred to in verses 5 and 6. There is detailed commentary on this in the Karika. The verses state:

  1. That is the state of deep sleep wherein the sleeper does not desire any objects nor does he see any dream. The third quarter (Pāda) is the Prājña whose sphere is deep sleep, in whom all (experiences) become unified or undifferentiated, who is verily, a mass of consciousness entire, who is full of bliss and who experiences bliss, and who is the path leading to the knowledge (of the two other states).

  2. This is the Lord of all; this is the knower of all; this is the controller within; this is the source of all; and this is that from which all things originate and in which they finally disappear.

  • Thank you, this thought experiment was ideated just after reading that wonderful Upanishad! Commented Aug 3, 2018 at 6:03

You seem to be talking about substrate independence, not body independence. And then you just assume it (between you & copy; that you are 'like' a music file), so not really demonstrating anything.

Sure from the subjective point of view nothing changes. But not from the universes: hence there being anything to puzzle over. We knit together our realities from cross-referencing all the information we have. Yes in special circumstances that could be wrong, we are limited fallible beings. So what? Science is just our best tentative conclusions, on the balance of evidence and probabilities. Just do science. You are not independent of the universe, the gravity generated by every speck of energy and matter in it criss crosses your body right now. Your consciousness may feel independent, but it crucially depends on causal chains of evolution and language and childcare that are preconditions. You aren't a Cartesian 'I' only just tethered to the world and causality.

Are you the same person when you wake up that went to sleep? Have you been reconstituted correctly, and what might that mean or feel like?

Surely of far more interest than susbtrate independence, are systemic distortions, and the processes for examining and discarding them. What does it mean to have continuity with our past and future selves in practice? Given the limits on our certainties, how should we decide to be, so as best to adapt to that? Maybe holding our knowledge of ourselves more lightly, would be a first step.


If there was an afterlife, the hidden premise that the consciousness of the original sleeper would cease to exist would not hold. Instead, the person would wake up to face whatever afterlife there was: Tartaros, Judgement day, or others have been suggested.

So, the result could be that one consciousness is facing some form of life after death, while there'd be a second "equal but not identic" consciousness of a person who believes to be the same as the killed person... while the second person couldn't know the difference, the first certainly would.

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