I have a brain (A) that consists of certain atoms in a specific combination (C). If I destroy this brain, and afterwards regenerate the brain with the same atoms and combination (C), is this still brain (A) or a different brain?

If I assume that this is the same brain (A), then let's do this thought experiment:

I replace the atoms with different atoms, but of same type in the exact same combination. If I assume this is not brain (A), but brain (B), then there must be a difference in two atoms of same type. Time could also be a difference. However, scientists haven't found any difference in two atoms of same type. So is the consciousness of the new brain (B) the same consciousness as belongs to brain (A), or are they different?

  • Empirically, we have no idea. We can't actually do what you describe, nor can we record and differentiate subjective experiences. So how would we know whether the two structurally identical brains (Theseus I and Theseus II?) were experiencing the same consciousness or not?
    – Jedediah
    Commented Dec 14, 2021 at 19:28
  • Roughly as the answer has noted, although the brains may be similar or even copies, each has its own, distinct sense of subject. Like two similar places, each has its own distinct sense of "here". Various philosophers have noted the similarity of subjective experience to concepts of "here" and "now". They are unique to each instance.
    – Nikos M.
    Commented Dec 14, 2021 at 22:01
  • The same thing thing that makes two different robots function independently, even if they have the same shape, composition and programming. "Consciousness" is a dynamic process, not a function of intrinsic properties.
    – Conifold
    Commented Dec 14, 2021 at 23:03
  • 1
    Does this answer your question? The "Brain" of Theseus?
    – Conifold
    Commented Dec 14, 2021 at 23:05
  • Microscopically: "I have..." is wrong. It should be: "I had...", giving that atoms change and move constantly. A large portion of atomic "combinations" are not persistent. Macroscopically, you can't perceive atoms. But you seem to be the same person than 5 seconds ago on the mirror. Even if that is microscopically false. "Macroscopically" is determined by the senses, understanding and reason. So, the term being (is this still brain A or...) is quite subjective.
    – RodolfoAP
    Commented Dec 15, 2021 at 11:44

4 Answers 4


I think we can apply occams razor here

We know that human individuals are pretty similar, we even have twins.

We know that human individuals don't share consciousness or have any form of telepathy.

If we copy a brain exactly there is no reason to suggest that this would be qualitatively different from any other pair of individuals.

  • As an observer there is no difference, but what about the subjective counciesness? Commented Dec 15, 2021 at 16:44
  • what do you mean?
    – Ewan
    Commented Dec 15, 2021 at 16:53
  • I suspect @EliasKnudsen means "another person looking at the clone would be unable to discern a difference ... but would the clone themselves have a different subjective experience from the original person? Would they think they were different"
    – Brondahl
    Commented Apr 30 at 16:39
  • Unfortunately, the question is pointless to ask. We don't and cannot ever examine either half of the question - we can neither perform the atomic cloning, nor examine the internal subject experience - and so can never capture any data offering any insight into the answer. All that leaves is people, frankly, making up answers based on their own opinions and belief preferences
    – Brondahl
    Commented Apr 30 at 16:43
  • Their comment is confusing because in my answer there isn't an observer not seeing a difference. there aren't even clone brains to compare, or think about themselves. I'm just pointing out that there's no reason to expect anything crazy to happen.
    – Ewan
    Commented Apr 30 at 20:13

I have a brain (A) that consists of certain atoms in a specific combination (C). If I destroy this brain, and afterwards regenerate the brain with the same atoms and combination (C), is this still brain (A) or a different brain?

It is a copy of the brain (A), and not the brain (A) itself.

The (A) and copy of (A) are identical to each other, however, their object reference differs; they refer to different instances of (A), ontologically. Also, see indexicality.

For example, two thought experiments:

  • If you create two exact printer machines from a single factory blueprint, are they one and the same printer?
  • If two ants were born with identical anatomical structures, would they share the same mind?

(I think it's rather extremely counterintuitive to say Yes to neither of the above.)

  • 1
    In standard classical logic, you cannot say that equality between copies holds, because objects at different locations cannot be the same object.
    – user21820
    Commented Dec 14, 2021 at 20:49
  • Your comment doesn't make any sense. Mathematical equality is based on exactly the same equality in classical FOL. You do not seem to understand classical FOL...
    – user21820
    Commented Dec 14, 2021 at 20:55
  • The fact that you ask confirms my point that you do not understand classical FOL. I did not upvote your post, because it is simply wrong. I encourage you to learn FOL, otherwise all your reasoning (as in your post and comments) will be at best sloppy and at worse invalid.
    – user21820
    Commented Dec 14, 2021 at 21:15
  • @user21820 In my thought experiment i meant that everything happenes at the same position. However time is the only difference. Commented Dec 14, 2021 at 21:56
  • @user21820 If I can say that triangles ABC and A'B'C' are identical, then conversely, I can say that brain (A) and copy-(A) are identical. It seems that it's what the OP meant, nothing more, nothing less. Absolutely no one needs to learn FOL to understand this, otherwise a toddler couldn't distinguish between getting the same toy for the nth time in a row. Moreover, there is no productive need to get into the quarrel over the particular meaning of 'equality' where there is no need to, due to a rather clear context it is used in. Commented Dec 14, 2021 at 22:31

Problems of this type are grouped under teletransportation paradox thought experiments.

A useful concept is the idea of substrate independence, that while we depend on a particular physical manifestation, we think other modes or media could be doing the same thing. Chalmers thought experiment 'Fading Qualia' examines this issue.

In short, yes our intuitions about identity are deeply suspect. A substantial part of Buddhism is about investigating this, & they conclude there is a deep universality about awareness itself, & reality we experience is emergent & co-arises intersubjectively as illustrated by the metaphor Indras Net. That includes manifestations of identity, which occur in specific contexts & relate to attachment to specific narrative threads.

There are no universally valid answers because of this. The meaning of identity will depend on context, eg access to bank accounts, liability for criminal prosecution, the relationship with a partner, etc etc. Who is asking, why where & when, must shape any given answer.


This thought experiment, which is similar to one I discussed with a friend in 1968, tends to show that the isomorphism class of the physical phenomenon is not what corresponds to the resulting consciousness. Instead, what matters is the exact identity of the collection of matter that is involved.

(By keeping only the "isomorphism class" we refer to replacing some atoms by identical atoms.)

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