I saw this question somewhere in the Internet(I forgot the source) and I think this forum is a good place to ask it.

According to what I know, the atoms in a persons body are replaced every certain amount of years: https://skeptics.stackexchange.com/questions/18427/are-all-the-atoms-in-our-bodies-replaced-on-a-regular-basis

Then, if a persons body atoms are replaced every x years, should the person be prosecuted today for a crime that he/she committed x years ago, when today that person is physically another person(different atoms)?

And lets say hypothetically that 0.00001% of atoms are never replaced, should 0.99999% of the sentence in years be eliminated (the person is 0.00001% responsible for the crime) ?

This is a related question in the forum: Am I still the same person as I was yesterday?

  • 4
    If not, by the same reason you will not be paid by your company at the end of the month... Mar 15, 2015 at 18:58
  • I have an idea; Maybe instead if thinking of people in terms of atoms, is better to think of people as information. The physical self of the person may change, but his/her information(memories, motivations, passions, etc) may still be present x years after committing the crime. Hence the person should be still be prosecuted because, his mental "software" may still be present x years after the crime is committed.
    – user63152
    Mar 16, 2015 at 1:54
  • So if I told you that all of the atoms in your body would be different a year from today, and that any crimes you commit today would not be punished till next year, would you figure that you can commit crimes with impunity?
    – WillO
    Mar 16, 2015 at 13:37
  • Heraclitus and Christ both probably say no. But who listens to them, really?
    – user9166
    Mar 16, 2015 at 19:02
  • You can't prosecute or punish atoms. They will have no awareness of being 'prosecuted' or being 'punished'. The one that is being prosecuted is the 'awareness' inside the body that is aware of prosecution and punishment and also has recollection of the transgression committed. Mar 17, 2015 at 7:17

4 Answers 4


Atoms do not contain little tags that say "I am part of user63152", and whose unique properties determine the actions of user63152. Indeed, aside from differences in isotopes, and a handful of observables like nuclear spin, atoms of the same type are indistinguishable from each other.

Thus, we needn't care whether the atoms are replaced every minute, every decade, or never. That ongoing entity which is you is you by virtue of emergent properties (like thought) which are robust to changes in which atoms you are made from. So while time may have some bearing on how we choose to prosecute crime, it should not be because there has been some swapping around of functionally equivalent parts.

  • But anyway, we need also some sort of "physical stability" in order to "support social interactions" (fingerprints, retinal scan). Without them, we are in trouble ... If my identity is only in my "inner self", there are possible situations in which I may have problem to be "recognised": what about my bank account ? Mar 16, 2015 at 15:19
  • Mauro, between the atoms in the body and our "inner self", there are many biological layers, with different rates of substitution. Anyway, I think our bank account is only based in a legalist view of your "self" as an ID number.
    – Rodrigo
    Mar 16, 2015 at 17:24
  • Say due to radioactive exposure/mutation of DNA a person's "tag" i.e., their DNA changes this person had done a crime in the past, should this person now be criminalized or not?
    – How why e
    Feb 13 at 10:14
  • @Howwhye - The person would be dead approximately a billion times over before their DNA wasn't easily recognizable as that of the original person. This isn't a concern in practice.
    – Rex Kerr
    Feb 14 at 1:13

Arne Naess wrote many essays about the Self. In them, he argued for a concept called the Ecological Self, but along the way he used a series of phrases to challenge commonly held approaches to defining the self. Such class of phrase pairs looked like:

  • I enjoy listening to Mozart.
  • My body enjoys listening to Mozart.


  • I am my mother's son. ("daughter" if you are female)
  • My body is my mother's son ("daughter" if you are female)

If one considers the pairs of phrases to not be quite identical, it suggests that "my body," i.e. the atoms in my body, are not quite exactly the same concept as "my self." Thus, replacement of the atoms in the body is probably not sufficient to be a change of self.


What is the purpose of punishment? If it is to link consequences to decisions, then the question is whether that old collection of molecules should have predicted the damage it would cause any better than this new collection of molecules.

Our notions of learning imply that behavior is a feedback loop and the consistency of personality is unrelated to the set of molecules that embody it, but related to the information that flows through them. So by and large, the prediction of recidivism remains good over long periods of time. Our morality gets no better with time, and the corresponding replacement of molecules, unless something else changes.

The better question is whether you should incarcerate, for instance, an amnesiac, or an addict who has just undergone something like ibogaine therapy, a rapist subject to chemical castration, or a terrorist who has undergone a religious conversion: a person who really feels like a 'new person' and has had a real part of their personality deactivated or removed in a way that has statistically proven likely to change current and future decision making.

  • How could you tell if they are really a new person, or if they were really a good liar? The liar should be further punished. So, we punt and leave them in prison. Better to wrongly punish one person than to hurt many by releasing a liar. "By their fruits ye shall know them."
    – user16869
    Sep 7, 2015 at 22:35
  • That is irrelevant. I am not talking about implementation, but about the morality of the punishment itself. You cannot know the court process that establishes guilt is ever right, or if the lawyers are just good liars. Does that mean the punishment is always undeserved, because of what we can't know? "If you free someone of their sins, they are free, and if you hold them bound, they are held bound."
    – user9166
    Sep 8, 2015 at 0:11

It seems to me that this is just a reformulation of Theseus' paradox. Plutarch notes in his biography of Theseus that the ship that Theseus and the other Athenian youths returned upon was preserved by the city of Athens through the ages. As various planks and rails rotted, they were replaced leading to the question commonly discussed among philosophers over whether or not the ship we have now is one and the same as the ship that Theseus returned to Athens upon.

Really the question at hand is the very question of identity. It's not an easy question to answer. A good starting place is the subtopic Understanding the Persistence Question over at the Stanford Encyclopedia of Philosophy in the Identity entry: http://plato.stanford.edu/entries/identity-personal/#UndPerQue

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