The Ship Of Theseus: Revisited In The 21st Century

Over the course of around seven years, your body replaces itself – bit by bit. Every cell in your body dies, and is replaced by another.

So, how are our identities maintained? What is it about ‘me’ that persists? If (as I believe is the case) the mind is physical in nature, then how can the idea of a continual ‘self’ make any sense? Should we even be responsible for the actions of our previous versions of ourselves?

These questions are raised in a thought experiment known as The Ship of Theseus, and it works as follows.


The Ship of Theseus

In Greek mythology, there was a king named Theseus who founded the city of Athens. A great naval warrior, the Ancient Athenians dedicated a shrine in his honour by preserving his ship in the port. The “Ship of Theseus” remained for hundreds of years. However, as the ship became old, some of the wooden planks started to rot. So that the Ship of Theseus was maintained properly, these planks were swapped with new planks made of the same material.

This is the crux of the thought experiment: how many planks must you replace before it is no longer the Ship of Theseus? This thought experiment makes for one of the more fascinating problems in philosophy – the problem of identity. What is it that allows things stay the same even after they change? At what point does an object become different? When we talk about an object and say that “it changed,” what even is the “it”?

The Problem At First Sight

At first you might think, ‘of course replacing one plank of the ship doesn’t change its identity.’ Maybe you think that you’d need to replace every plank of wood before the identity changes. Or is it that the Ship of Theseus’ identity never changes, because it still holds the same form. These are all reasonable answers to the problem, and none of them are necessarily false, however they aren’t particularly correct either. The problem has no definitive answer, and I don’t intent to give one in this article. What I am interested in what this problem says about the nature of who we are in the 21st Century.

The Problem For 21st Century Physicalism

I believe, wholeheartedly, that the ontology of the mind is physical. The mind is not some fundamentally unique nomological dangler that doesn’t subscribe to the laws of this universe.

I also believe the following, and I challenge anybody to dispute me in the comments below. Continuity of identity is possible and does happen – I can know this via introspection and this knowledge is subjectively incorrigible. I am the same self that woke up yesterday, and I am the same self I was eight years ago. When I see photos of myself as a child, I am looking at me.

So, where does that leave me?

  1. The mind (and so the self) is physical in nature (the mind is part of the body)
  2. The self remains constant over time.
  3. The body doesn’t remain constant over time.

As per Leibniz’ law, surely these beliefs I hold entail a ‘Reductio ad absurdum’? Is this not a paradox even?

Well, taken at face value, they do.

My Solution To The Problem

I believe that ‘self’ and ‘mind’ have been conflated to give rise to this problem. It is not that the mind is physical such that the self is physical. The mind is the collection of experiences that make up my qualitative existence. The self is a more nuanced concept, identifying the relationship between previous versions of me.

Because there is nothing physically the same about me now and me ten years ago, there is no thing that is the same about me now and me ten years ago. Therefore, the concept of ‘self’ cannot be a part of the category of ‘thing’. To borrow the language of  Gilbert Ryle, I think considering the ‘self’ as a thing would be to make a category mistake’.

Think of it like a program on a computer. By replacing each part of the computer one by one, never inhibiting the computer from performing its function on the screen, there is nothing about the computer that is the same as before I started replacing bits (and therefore there is nothing physically the same about the computer program too). However, it is the fact that the computer has remained functional, performing its program without fail, that it is possible to identify the continuation of the identity of the computer. I believe this is how personal identity works too.

Although over time my body (and therefore mind too) changes completely, the continued functionality of my mind never left. Every time I wake up, there has not been a significant enough change to my body that I fail to identify as the same person that went to sleep. My conscious experience of who I am is sustained through all the bodily changes that occur over time, because these changes are individually insignificant.

The self, then, is not attached to any physical thing, but is an emergent property of the aggregate of our bodies. To change the body slightly is not enough to change the emergent property. Therefore, the possibility of continual identity even when there is no continual mind or body remains, and the paradox outlined earlier fails to disprove either a physical mind or the possibility of sustained personal identity.


Check out this great video I found that explains the paradox of The Ship of Theseus in ninety seconds:


What do you think of the paradox of The Ship of Theseus? Do you agree with my interpretation of a solution? Have your say in the comments below!



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  1. James,

    This is nice little summary of the classic problem and a good read! I will take up your call for a challenge.

    Specifically, I would like to challenge the point that collating thing and self arises in a category mistake. Defining Self as a relationship between different sets of experiences of being you, as I take your definition, is on the first reading circular. If we define the self as just a relationship of self through time, we don’t really get any closer to understanding what self means.

    I think this central, because if the paradox you try to overcome lies in the fact that your self is a non entity than its ontological status is the pivot of your argument. Further still, if we were to take your definition, we would find that we were only describing an ontological condition, underlying the possibility of their being change at all since the self, as you are defining it, is that condition by which the mind and body are recognised as physical beings. Hence, or otherwise, your argument that the self is not a physical thing because it names the relationship between physical body and experience remains incoherent because it does not specify clearly enough what that relationship is.

    If I might suggest, rather than considering the self not a thing, considering the relationship between the ontological status of self with respect to time may be useful!

    Thanks again for the wonderful read and keep writing! You’re inspiring me to write! All the best from America!


    1. Mitchell,

      Thanks for the response, I appreciate you taking the time to read my work!
      When I am defining the self it is not that I am saying it is the relationship between different individual selves – that would I agree be circular. The relationship is between all the different instances of our conscious experience of identity – not the identity itself.

      I do agree, however, that the argument I put forward fails to provide a specific clarification as to what this relationship is. That’s because I don’t know what the relationship is exactly! What I feel I have done is illustrate why this must be the ontological status of identity.

      Once again thanks for your comments! I really appreciate it.


  2. Hate to be that guy, but you brain doesn’t really change. Your neurons are basically just your neurons all your life. They don’t really get replaced the way most of your cells do. Also your computer analogy is bad, because once you start replacing the RAM, you are literally pulling the program out of the computer if its loaded and running, unless you are switching the program into other places in RAM on-the-fly, which doesn’t really happen with computers. Also you’d run into issues when replacing the CPU if you don’t have multiple cores, because computation would literally stop while the CPU is gone.

    That said, it may be possible that, if our subjective experience is a continuous kind of thing, replacing parts slowly may not interrupt anything.

    1. Benji,

      Thanks for your reply! The computer analogy was put there in order to help conceptualise my point – if it’s a poor analogy then thank you for letting me know. However I still can’t see why replacing the hardware even an atom at a time would impede any processing. It’s not that the brain is replaced lobe by lobe – we are talking about microscopic transactions.

      Regarding your point about the brain cells, what is important is that the there are not enough cells that remain constant even for physicalists to want to claim that the cells are one and the same as the self. If this is the case then the argument stands and I believe it does.

      Does this change your opinion at all? Please do let me know if I’m still missing something!


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