Since every living being has a metabolism, we all live in non-equilibrium state. We keep on exchanging molecules and atoms with our environment. I assume that our brain is affected by this as well as the rest of our body.

So while my atoms keep on changing while I'm writing this, why am I still the same person, or better the same conscious being as I was tens of years ago?

(I was pretty shocked when I realised that the first time.)

I'm not speaking of growing up and being influenced by society. I just wonder, that all atoms of my body might be exchanged, without having an effect on my thinking. Does this mean, that there is something non-physcial (the mind or call it soul if you like), that can't be exchanged or can I influence my thinking by started to eat only carrots from northern france (just an example, not meant seriously ;-)?

EDIT Thanks for all your comments, so far. I would be happy to find some references to further read on the topic. Thanks.

  • 3
    There are those who would frown upon questions like this, because it does not cite specific expertise (this is "doing philosophy"). While we're still sort of hashing out modifications to our FAQ in meta, I would be in agreement with such a argument; the quick and dirty fix for this question is to turn it into a reference request for literature on psychological continuity (or more generally (but perhaps too generally) personality identity).
    – stoicfury
    Commented May 6, 2012 at 23:23
  • 8
    This is an old notion though, and you'll find lots of literature here. "Old" as in at least 500 BC old, when pre-socratics like Heraclitus said: "No man ever steps in the same river twice, for it's not the same river and he's not the same man."
    – stoicfury
    Commented May 6, 2012 at 23:27
  • 1
    @stoicfury: What? This is a classic subject for philosophy, from Buddhist deconstruction of the conventional self, to en.wikipedia.org/wiki/Ship_of_Theseus And in modern terms, we can evaluate which cells are replaced and which are not - some brain cells are conserved through our whole lifespan; and this can be linked to the conserved cell groupings between caterpillar & butterfly, for instance.
    – CriglCragl
    Commented Nov 12, 2020 at 3:46
  • In any hierarchy of complexity, atoms as the building blocks of cells on up to fully formed lifeforms to include human beings, it is only a starkly defined confusion to posit atoms on an even par, let alone to suggest that atoms are above us in any ascendency. Saying that because atoms 'change' and therefore we are somehow not the same person day-to-day is no different than suggesting that because 98% of our epidermis dries and is removed and replaced daily that this makes us a different person.
    – user37981
    Commented Nov 12, 2020 at 14:51
  • Check out Dennett's "Where am I" video on YouTube
    – Razor
    Commented May 23, 2022 at 18:45

7 Answers 7


It depends on what sort of philosophy one has, and even potentially what sort of practical issues one has to deal with in real life. Certain religious people might point to a soul, which keeps personal identity constant regardless of physical changes. General Semanticists following Alfred Korzybski would say no. Draks_yesterday (where _n indicates that we've subscripted the previous term) is not the same person as Draks_today since physical changes do occur. Also, people sometimes link memory and personal identity together. Given such a link, since no doubt your memory differs to some extent, your personal identity does differ today than yesterday. I pretty much agree with the general semanticists position here, and do think that memory does affect personal identity also. That said, the differences between Draks_today and Draks_yesterday could come as extremely tiny and difficult to figure out. On top of this, if you start to ask me about how we should deal with criminal behavior with this in mind, I might claim this as too abstract and philosophical to apply to criminals since such differences seem all too trivial compared to similarities, and the risk of overemphasizing the differences can become far too high with this sort of idea in mind.


There is an enormous philosophical literature on the question of identity, and the canonical thought experiment is the Ship of Theseus.

Suffice it to say that you'll find a wide range of opinions on this matter over the past couple millenia of philosophical thought, but you'll find very few people willing to argue that you are exactly the same as you were a few moments ago, and very few people who would claim that there is no continuity whatsoever between the you of a few moments ago and the current you.

Can you narrow down a bit what you are looking for?

  • Since I'm still kind of shocked when I think about that, reference are fine for the moment. Hopefully I will learn something and come back with more (philosophical) background...
    – draks ...
    Commented May 7, 2012 at 6:48

For an accessible article that, to my very limited knowledge, has philosophical relevance, see Derek Parfit's article "Personal identity". You can find it by popular search engines.

If you want less biased and broader approach, see for example Metaphysics: Conteporary introduction, published by Routledge. It discusses "Persistence through time" and gives further references.


I'd say, yes for the mostly, and perhaps my answer isn't the most philosophical but I will try to use science.

You are what you make of yourself, which is emergent property of a billions of neurons. Neurons don't exactly 'replace' or divide like most other cells going through mitosis in your body, say for example skin cells. This probably like the reason why you retain a lot of your memory (whether is accessible or inaccessible is another matter).
From this it follows, if you are your consciousness which is a mass cluster of neurons and neurons rarely in a lifespan and they are slowly growing, then you are mostly what you were yesterday. Obviously this changes if you got into an accident or had some significant moment occur in your life which dramatically altered yesterday's state.


There are at least two answers to the question "Am I still the same person as I was yesterday". Yes, and No.

It might be helpful to think of it with a fractal comparison. How long is the coast-line of an island? Well, that depends on what you measure it with. In the same way, it could be argued that, if I go to sleep and wake up - most days I'm the same. But, if I experience some major event or trauma, I might even say, "I'm not the same person I was"

On one level, I am not even the same person from second to second (choose your own unit!), because of changes occurring. We don't even need to separate physical and mental processes here, as we know that one affects the other.

On another level of course I am the same. If we accept that the definition of "person" implies someone moving through time from birth to death, then we can do away with the question altogether.

Now, I find myself thinking about what loss of memory means in respect of this question.... but I also need to get on with some work!

  • Question is over ten years old. Try to find a recent question, we find there are often similar ones here.
    – Confused
    Commented May 24, 2022 at 16:32

Answer these two questions: (1) Are "you" on the day of you birth and "you" one day before your death maybe in the 90's the same person? (2) If the answer to (1) was "No", then is "the same" meant in an absolute sense - can you be a little bit different from day to day and still be "the same", so that every day you are "the same" as the previous day, but after 90 years the changes have added up so you are not "the same" anymore, or would there have to be days where you were not the same?

(As an example: My height today is "the same" as my height yesterday. Yet if I or my parents had written down my height in centimetres every day of my life, there would have to be about 120 or 130 days where the height written down wasn't the same as the day before).

  • 1
    I'm not sure I see how this answers the question.
    – E...
    Commented Jul 30, 2016 at 14:54
  • It doesn't answer, it clarifies. It forces you to understand what you mean by "the same". Without that understanding, the question cannot be answered.
    – gnasher729
    Commented Aug 1, 2016 at 16:06

Is it true that the world did end on 2012 December 21 but we don’t remember and we’re now living on a new universe? But I also have one more thing to share on that same day and year I had something wrong with my tooth and I was playing around with it but then I remember just like zoning out for like 2 seconds and I felt weird like my old body was gone and I didn’t felt the same like I didn’t feel like I was living on the same world before but know I just feel like I’m in a video game or something

  • No, the world did not end on 21 December 2012. The end means... end. There is no point to end something just to begin again from the exactly same point.
    – lukuss
    Commented Apr 4, 2018 at 8:33

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