Scenario 1:

Somebody removed your brain, destroyed it, and then replaced it with another which was identical (and replaced all the connections as they were). Essentially every atom/molecule would be replaced by another of exactly the same type in exactly the same place.

In this situation, it seems reasonable to assume, if we assume that one's experience/consciousness is a product of their brain, that from your perception, you simply die. Your brain is removed and destroyed: whatever happens after that does not matter. It's just that there will now be a person who thinks they are you and that they have always been you (the new brain), but they are mistaken.

Scenario 2:

Your brain is replaced molecule by molecule, atom by atom, in a way that does not interfere with the working of the brain (each bit is replaced by an identical bit only at a time when that bit is not being used and so the process happening in the brain is not disrupted).

Is seems reasonable in this case to assume that from your perception, you do not die. (If this is not the case then would that mean you would die slowly, in proportion to how much of your brain has been replaced? How would your consciousness fade out if the process in your brain is not being affected?)


In scenario 1, the process is completely stopped and replaced by another idential process. In scenario 2, the process is not disrupted. This implies that consciousness is the process (or multiple processes?) happening inside the brain.

Therefore, does this imply that cases where people die momentarily (ie are brain dead and then reawaken), from that persons perspective they just die. And when "they" reawaken it seems to everybody else that they are back, but actually they have just been replaced with another completely identical person?

  • 1
    Hi, welcome to Phil SE. The question of identity under slow replacement is not unique to consciousness, see the Ship of Theseus en.wikipedia.org/wiki/Ship_of_Theseus Also, the brain is a neuronet rather than a digital computer, so the "time when that bit is not being used" is probably never. That aside, as with the ship of Theseus the question seems to reduce to a linguistic convention: when do we say that the object is still "the same" or not. But an answer makes no difference substantively since we know what happens and how. There is no "actually" here, it is a matter of convenience.
    – Conifold
    Sep 29, 2016 at 0:15
  • Thank you...it's probably obvious that I don't read philosophy lol Sep 29, 2016 at 9:28

2 Answers 2


Scenario 2 is famously presented by Chalmers as the "Fading Qualia" thought experiment - he uses it to argue that surely, consciousness is preserved, because it's implausible that such minor stepwise modifications which preserve functionality could actually be changing anything about our experience. Against him, he notes, Searle argues (The Rediscovery of the Mind, pp. 66-67) that in fact one's conscious experience would slowly fade (a gradual mental death, in effect) while one's behaviour remains continuous and unchanged. In today's terminology, one is slowly transformed to a philosophical zombie.

Within this debate, scenario 1 is a bigger puzzle. It relates to the teleportation paradox and challenges functionalists and non-functionalists alike. Roughly, it's often thought that to the subject the experience is continuous - sort of like waking from a coma with no sense of time having passed. From another angle, it gives reason to doubt true continuity of experience in somewhat Dennett-like fashion.

On the whole you've here reproduced rather seminal problems in philosophy of mind. There's a wealth of literature on both!

  • This is a good point. I took OP as talking about self-idenity rather than conscious experience/qualia. We do know what happens when relatively small parts of the brain are taken out of comission, the rest readjusts to compensate, sometimes in unexpected ways. So why not "phase transitions" in qualia rather than "fading". What I dislike about Chalmers and Searle type arguments is appeal to (non-existent) "intuitions" about that which we know little about, have no idea how to bring about, and with conclusions we can't test even in principle. This afflicts modal arguments in general.
    – Conifold
    Sep 30, 2016 at 17:16

this first comic in this philosophical comic strip looked at this problem http://existentialcomics.com/comic/1 it took it a step further and said that continuation of consciousness is also an illusion and that our past selves are dead and our current self will die shortly and our future self will take over only to die and be taking over by the next future self.

So, if we take that logic, scenario 1 and 2 end up being the same in that we are never the same from moment to moment, our feeling of continuity are a result of our brain configuration.

  • Nicely put - this is exactly what I meant with my comment about doubting genuine continuity of experience. It is, by some lights, the only coherent answer to the puzzle.
    – commando
    Sep 29, 2016 at 7:07

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