The Big Question: The Ship Of Theseus

That's right, I went there. It's a real big question. Crazytown on Kotaku today. I have faith in you, Kotakuers. Together, we can solve this philosophical classic. It goes like this...

You have a ship. Over time, it gathers wear and tear. Its crew repairs it, as needed. Parts are replaced — both small, like individual planks, and large, like a major sail, or eventually a mast. It all happens a little bit at a time.

After a while, the ship is made of completely new parts. Is the ship the same ship? Or is this a different ship? Theseus has been texting me about this all day and won't leave me alone until we get back to him.

[Ship] via Shutterstock


    Point to the exact moment where it stopped being the same ship.

      when the final piece that was present originally got removed

        But I've used that ship the entire time- it's in continuous use, and it never disappeared.

          But after replacing every single part of something, surely it can be now be wholly considered as a replacement and not the 'same' ship.

            Just about every cell in your body dies and is replaced over a matter of years. Are you still you?

              I think I'm a different person now then when I was 5 years old. Physically and mentally I am completely different. Yes I have the same name, belong to the same set of friends/family, but I am a different person. This ship may belong to the same person, carry out the same duties, but it's not what it once was.

              Last edited 28/05/14 2:48 pm

                Maybe philosophically, but if 20yr old you committed a murder out of youthful recklessness, the law isn't going to buy your, "I am physically and mentally a different person," monastic 40-yr-old self, when it finally catches up to you. Far as the cops are concerned, you're still that one what done it.

                However the new you is a result of being the old you and growing up. It is impossible to retain the old you and the new you couldn't possibly exist at any point in time without the old. And all the time, you are you. Things have changed, but not been completely superseded in function or essence. In fact, many things haven't changed at all!

                Similarly, the ship is more than the sum of its parts, especially in its interaction with human beings. Moreover, drawing such a fastidious distinction in nature based in composition, could be easily pushed ad absurdum. A few minutes after sailing, the chemical reactions of the sea water on the wood would dramatically change it's composition, initiating slow but irreversible processes of oxidation, calcification and putrefaction, depending on the kind exposure. After a few days, there wouldn't be a single plank in the whole ship unaffected by seawater even if only slightly so. Is it a different ship, then? Only in the most technical of the senses, but I think we can agree that this is a difficult question because we're not talking about measurable realities but about abstract ideas about the "nature" of something.

      Each is an entity that travels upon its own path through time. At each quantum of time it becomes a new entity in which its composition may vary relative to the previous state. Therefore it is the yardstick by which you measure time that one stopped being the other.

      Last edited 28/05/14 4:57 pm

    It you're refering to it as a location then it's the same ship.

    Does it have the same name? Totally the same ship, bro.

    Point to me when an Early Access Steam game that overhauls all of it's core mechanics, graphics and various other bits and bobs STOPS being that game and starts being a different game.

    Edit: Also, screw you for making me use the word bro unironically. Damnit, I have to go hand in my fixie, my regular quinoa shoppers card and my beard to the nearest hipster department.

    Last edited 28/05/14 12:28 pm

      What about if the same game re-releases under a new name in the hope of shedding negative press?

        It's still, unfortunately (or fortunately), the same game. @puck and you put it much better below - this is based off the idea, the concept, rather then from the base mechanics and materials that make something up.

    Grandpa's axe.
    Conceptually, it's always the same object due to the way we define it. Because there's only one. It's going to be the same dilemma when it comes to teleportation - create a copy somewhere else and destroy the original. Is it still the same thing / person?

      I love the episode of Star Trek where a Doctor (not the onboard Dr) refuses to use the teleporter for this reason. She believes she instantly dies at the ship end and an exact replica is created at the other end.

      Yeah that's always freaked me out. I copy and paste a digital file, to me it's the same file in every practical way, but of course it's using different physical bits to exercise it's existence. If we figure out large scale teleportation, then that could really mess with people's sense of self, especially if the original isn't destroyed. I can imagine that if you're the person walking into the teleporter, your existence would be cut short immediately, but if you're the person walking out, you'd testify that it all worked perfectly and you were just walking in on the other side only a moment earlier.

        The destruction of the original would be utterly essential to any teleportation thing or you'd rapidly get black market cloning, sex slaves & organ harvesting gangs cropping up. Any chance of making a copy of a person on the sly and you know that some arsehole would go down that road.

        Once we hit that technological stage, matter & energy would be considered basic resources and presumably if I were to teleport from Wagga to... Helsinki for example, my 186kg of matter/energy would be dematerialised while my data is sent across the network, my matter/energy is stored in a resource bank and those resources used to reconstruct the next 186kg worth of passengers coming to the Wagga transport terminal.

        Obviously there'd have to be some manner of verification system in place to ensure safe delivery, your pattern is saved in storage until you enter some personal details at the other end to ensure you appeared correctly, if not they can junk the dud copy (which would cause all manner of human rights issues if a copy wasn't entirely perfect but still a viable human) and try another transport.

          There'd be so many repercussions to that level of technology that it hurts my brain. I'm sure you'd step out at the other end of the teleporter with a sudden hankering for a nice cold can of Coca-Cola(TM)!

          You'd be able to save backup copies of yourself as well, so if you were ever in an accident and died the only thing you'd lose are the memories up to the last backup - although at that level of technology they probably be able to wirelessly upload your memories as well. Maybe at that stage we'd actually never go out in our real bodies, we'd just sit in a tank and our consciousness would hop from one body to the next, as long as it was within range of the nearest consciousness transmitter.

          It hurts my brain particularly because I get the powerful impression that I'm an conscious individual entity, separate from my body, who is basically seeing out of the window that are my eyes, when in fact I believe that there is no distinction between body and mind (and the impression consciousness) at all.

          Last edited 28/05/14 1:26 pm

            Ever seen a show called Earth: Final Conflict? They had "peaceful" aliens living on earth and having the equivalent of teleportation tech, in one ep, people got delayed in transport and then showed up later apparently fine but it turned out that they'd been sent to the alien's secret moonbase and implanted with mind control tech

              Haha brilliant. Seriously though, once we can disassemble and reassemble atoms, it would be trivial to take the further step of making slight adjustments to a person when they came out the other end. Go in voting one way come out voting another.

                That level of precision manipulation would be extremely complicated and would have to be tailored to the individual since moving a few atoms to the left in one person could make them strongly conservative but in another person it could make them so unhinged they become a serial killer. It'd also have to be really subtle or people would say "Brian used to be an atheist campaigner for gay marriage but as soon as he teleported to Berlin, he started wearing a God Hates Fags t-shirt". If I were manipulating people, I'd be more likely to go down the route of making them receptive to key phrases or something along those lines.

                The best countermeasure would be multiple data checks enroute. Say each time the data set passes through a router, it's checked for integrity and rejected and the person rematerialised at the last hop before the data was altered. The system could be built so passengers were scanned prior to entering the transport room to establish a baseline pattern and scanned again immediately before transport starts to compare them. Each transport pad could be an isolated unit to further reduce the possibility of tampering so if anyone wanted to corrupt a person in transport, they'd need to trick the incoming scanner, the transport scanner and all the router integrity checks as well as having a very specifically tailored method of interfering with a person's pattern without killing them or being obvious in their alterations.

                The same mechanism could be used for general safety; make sure transports go through a minimum of 3 routers no matter how far they go, each storing the pattern until the next hop verifies complete and correct reception, any failure means the person is rematerialised at the current station. Keeping the individual transport pads as isolated systems means that a catastrophic malfunction would only mean the death of one person rather than everyone in that transport.

      But what if I hand my grandpa's axe down to my son, who never knew grandpa,
      it's most likely my son would call it dad's axe, so is it then the same object?

        Nice. In this case, I'd say yes it's still the same object, since there aren't two separate concepts. It is still The Axe. There'd have to be an acknowledgement of Grandpa's Axe, and Dad's Axe, and something that distinguishes the two as being different. Like if when the handle is replaced, it's a dark wood, but in pictures of Grandpa with Grandpa's Axe, it's light wood. To the father that replaced the handle, it could be the same, but to the son, it has no conceptual overlap.

    Cells in our body do the same thing, but we remain ourselves. It's because labels like "ship" or "person" refer to an idea of the whole more than to physical substance making up that whole. A waterfall isn't the water itself, which is continuously replaced, but rather our perception of a system which involves the sustained event of water falling.

      not every cell does it though. neurons in our brains are never replaced, so for all our lives, we have a group of cells that remain constant, even if the rest of us changes...

        That's slightly reassuring for some completely illogical reason :)

          Or not when you consider that they can degenerate and die off...

      Actually, the negative argument in the Ship of Theseus paradox extends to the human analogy as well, by arguing that we are not the same person we were before, and that our identity is in a constant state of change. You can look at a photo of yourself as a 5 year old and say 'that is me', but it's not strictly true. The you that exists today no longer shares the same identity as the 5 year old 'you' in the photo - your identity today is no longer one of a child with all the wonders of the world still ahead of them, dependent on your parents for learning and survival and yet unable to contribute meaningfully to the world around you; but of an adult with experiences and behaviours and reactions unique to how you are now. And as every moment passes, so too does your identity change.

        That's a really cool way to look at it as well. It really comes down to how we use labels, and the way in our minds their definitions often have hard edges for the sake categorising, but in reality the boundaries between ideas are much more fuzzy. This leads to all sorts of problems that can't be easily solved from a category-based paradigm, such as "when is a foetus considered to be a person", "when is a child considered to be an adult". In the end we just arbitrarily reach an agreement on what a label defines and draw the line there.

        It just comes down to agreement I think. Is that the same ship? If we all say it is then it is! I imagine walking up to a King surrounded by his guards, and saying "Let's all agree that I'm the king now, kill that imposter!" and if I'm convincing enough and the guards come to a consensus, then now I'm the king. In reality the guards would likely reject my claim of being the king partially because in their minds they have a consistent idea of who the king is. Just as somebody viewing the ship would see it as the same ship if it didn't break with their mental image of it as time went on. If it closely resembles their recent memories, it passes the consistency test - the change has to be gradual so people can accept it and adjust their mental models. If you replaced the ship all in one day (or replaced the king), they wouldn't have time to update their definitions, it would be too jarring and they would reject the label.

        Seriously though, I'm the king. I'll treat you better than that old king what's-his-face. Are we all in agreement?

          We tend to place value on visible or easily recognisable qualities when determining identity. If you walked in and said you were the king, the guards would reject you because you don't resemble the king. But if you did, in fact if you resembled him exactly, how would the guards react? Probably with confusion, because to their eyes now there are two kings, but they know there can't be two kings so they struggle to find something to differentiate between them.

          But if you, resembling the king exactly, entered his bed chambers at night and murdered him and then took his place, nobody would question it. Even though you are not numerically identical to the now-dead king, you are sufficiently qualitatively equivalent that you could effectively usurp his identity in the minds of the people.

          Does that mean you actually have taken the identity of the king, though? This ventures into the notion of relative identity, where identity only exists in a relative context between an observer and the observed. To the guard you're the king. To the peasant you're the king. To the queen, she might have her suspicions in the bedroom, and to you, you know you're not the king that was there before.

            Yeah absolutely - so if the ship had the same name painted on the outside, and it generally resembled how it's always looked, and there wasn't a duplicate floating around to confuse people, then that would convince most (non-philosophers) that it was the same ship, which I think in turn makes it the same ship. So I don't personally think definitions have an existence outside of the human brains that defines them

              "which I think in turn makes it the same ship"

              That's quite an assertion, and possibly a non sequitur. Can you show how to reach that conclusion by way of logic?

              I mentioned briefly in a reply below, but I think you may be confusing labels with identity when the latter is a much more base concept. Consider the hypothetical situation where you believe anything I tell you. If I place an apple on the table in front of you and tell you this is an orange, you believe it and you call it an orange. Then without changing anything I tell you it is in fact an apple, and you believe it and call it an apple. The label for the object has changed, but has its identity? Is the apple when you call it an apple different in some way from the same apple when you called it an orange?

                So for me, a label is an object's identity. By label I don't mean it's name, I mean it's definition, it's identity according to an observer. You've changed the name (from orange to apple), but that's just changed my idea of what to call the object, not my idea of it's identity. So when you ask "The label for the object has changed, but has its identity?" I would say: its identity, for me personally, has changed, because it has no identity outside of our definitions of it.

                If through some alchemical process you change an apple into an orange, by changing the anatomical structure of the fruit while retaining all the same mass and energy, I can now call it an orange. A label of it can change, because a label is a subjective consensus, but what becomes of the "fundamental identity" of the apple? Has it changed as well? If that's the case, then how is it different from a label, how is it fundamental?

                Last edited 28/05/14 3:46 pm

                  I feel like we might miss something going between both threads so I'll leave it to the later thread for my replies =) I think I addressed your question there with the definition of identity in philosophy.

    I remember first wondering this in one of the Herbie movies. The one where he's with the lady at the old fire station, they mention how he's had all his different parts replaced over the years and stuff. Made me wonder how exactly he's the same "person" or whatever. I guess since not all the parts are replaced at once, they each carry their own experience and signs of wear and tear through the life of the ship, so in a way it's still the same ship. But at the same time, it's not the same physical ship you started with.

    Last edited 28/05/14 12:34 pm

    Was serenity a different ship after the events of both the tv series and the stripping down and defacing it got in the movie? nope.
    The Mary Rose was basically rebuilt from the ground up after a number of battles left it in tatters and was still the same ship when they salvaged it from the sea floor.

    An object is nothing but a pattern. if the pattern is unchanged then the object remains unchanged, even though the material composing it, may. Take for instance a whirlpool in the ocean. It retains its shape, but its constituent particles are constantly changing.
    It is the same for humans and indeed all life. None of our molecules remain static, they are constantly changing and being replaced. Yet the human "pattern" remains more of less the same.

    a philosophical question pointing to a future where humans become something new, by our own devising.

    You gotta play Deus Ex: Human Revolution. He questions this the whole game.

      Well he didn't ask for it so it's only fair to question things

    In my view, you'd have to replace a minimum of 50% of something in one go to be a new thing rather than modified version of an existing thing.

    Recycling case, optical & physical drives on a PC while replacing PSU, mobo, cpu, ram, soundcard & GPU in one action? That's a new machine.

    Progressively upgrading the same components over a long period makes it the same, albeit upgraded, machine.

    Besides, as I understand ship construction (which is far from my specialty so I may be wrong), you can't replace the spine of a ship without basically pulling the entire thing apart and rebuilding it from scratch. As long as it has the spine it'd be the same ship

    What is a ship without its crew? After all the repairs and replacements, is it still being manned by the same crew?

    It's because you're looking at it wrong man...

    A ship isn't a few bits of timber and some cloth, it's not a collection of men and ropes... it's a statement of intent. It's a representation of a nations authority, and a floating embodyment of her hopes, and dreams, and aspirations. It's a means to shift men, materials, and the balance of power.
    A ship is a regents promise to her people, no matter how near or how distant... it's an oath to her allies, and a warning to her enemies.

    From what you are saying it sounds like the ship is undergoing usual wear and tear, I would say that its unlikely the whole ship would be replaced over its lifetime. The bare bones and main structure that holds it together would not be replaced (well from my thinking it would be quite an expensive undertaking and probably not worth it to replace a whole hull of a ship).. plus I suppose as humans we tend to create bonds with inanimate objects and try to give them a soul of their own (like when people name their cars and literally their boats) so it would be more of the memory created around the ship that continues with the newer parts included.. similar to how we are the same person even though our cells are fully replaced every 7 or so years..

    It's the same ship because all of the parts are of different ages and replaced at different times. At no time are all the parts replaced all at once otherwise that would be considered a different ship albeit with the same name.

    It's a question about identity really. If I turned into a dog right now, am I still myself? Or have I become an entirely new existence, separate from who I was moments ago? If I could convince you that a dog in the room was actually me having been turned into a dog, would you still recognise it as me because you believe it is, even though it really wasn't?

    As an extra philosophical question, if, during the night, someone replaced the ship with an exact duplicate and no one ever found out, is it the same ship?

      I was starting to worry that nobody here really appreciated the philosophical paradox presented by the Ship of Theseus, but you've restored my faith =) The Ship of Theseus is an identity paradox, intended to outline the difficulty we have in separating qualitative equality from numerical or literal equality. The old and new ship are qualitatively identical but they are not numerically identical, in the same way two copies of a file on a hard disk are qualitatively identical but not numerically identical.

      Personally, I find elements of both sides persuasive, but I believe the solution is in transitive identity - the identity of all things is in a constant state of change, and the identity of something now is never the same as the one it had a moment ago. The two identities may be qualitatively equivalent, but are not the same.

    Kotakuers? People (i.e. us) who read Kotaku are Kotakuers? I would have said Kotakuans (like people from Nauru are Nauruans), or being a word borrowed from Japanese, Kotaku-jin?

    From memory, this question has a second part, which is:

    What if all the replaced parts are kept aside, and once every part of the ship has been replaced with a new part, the old parts are used to reconstruct the ship. Which then is the "real" ship?

    My answer is they both are, and yes it's a paradox. Get over it and have fun with your ship.

    when i get a radiator replaced in my car, or fit off new tyres, its still the same damn car!

    had the replacement parts been upgrades, like say you put in bigger canons, a better mast, different type of planks, new battering rams (too much Black Flag) then i suppose its different, but not completely different, more like a modified/improved version of said ship...

    There's a very zen-like answer to this (one of many really), which I prefer.
    Think of a river, the water running through a river constantly changes, but we still identify and relate to it as the same river, even though the contents (water, dirt etc.) is shifting around.

    The ship is the same ship, as that is what we know it as.

    The HMS Victory which now stands as the oldest complete wooden ship in existence has very few oak planks that are original to the ship from when it's keel was laid 250 years ago. Mainly some lower structural beams and such. Everything else has been replaced in time due to rot, war damage or for upgrade reasons.

    Is it still the HMS Victory? You bet it is. Has it got any original parts from 1750? Hardly any

      You don't address the paradox here though. On what basis does a ship made up of no original parts retain its original identity? If all the removed parts from the original HMS Victory were reassembled into a full ship and placed beside the current HMS Victory, which one is the real HMS Victory?

        It's only a paradox if you believe labels have meaning beyond what we agree upon. If you assembled the original parts into a full ship, that wouldn't make it the HMS Victory because we've come to an agreement that the ship made of no original parts is the HMS Victory. If somebody comes forward and puts out a passionate argument that it is indeed the HMS Victory, and everybody is swayed, then now it is the HMS Victory and the 'no original parts' version isn't.

        Which one is more correct? Neither, they are just agreements, To argue that that agreement could be wrong makes the (I believe) incorrect assumption that there is any objective right or wrong in the matter at all, rather than just consensus.

          The paradox looks at identity though, which is something of a more foundational notion than labels. Forget the name 'HMS Victory' for a moment, if we point at the original HMS Victory and refer to it as 'this ship', qualifying its identity by scope, and then point to the modern HMS Victory and refer to it as 'that ship', is it correct to say 'this ship is that ship'?

          Labels exist at a more surface level. I can call you duck, and convince others to call you duck, but it doesn't really change your identity, it's just the word we use to reference you.

          Last edited 28/05/14 3:09 pm

            I think get what you're saying, but I don't actually agree with there being a foundational notion of identity. I don't think there is a "this ship" and "that ship", there are only labels. When you say "this ship", what is a ship? How do you define a ship? Is it a collection of parts, or the atoms that make up those parts? You can say it has an identity because on a macro level is generally looks like an object that has obvious boundaries, but I believe that's just a definition you've given it.

            What is the difference between calling me a duck and calling the ship "this ship"? Each definition has created a boundary where none exists. Am I separate from the air, from the ground, from the universe? When I die my atoms, which were once in stars, will again scatter away and become part of different 'objects', each one given a label as it temporarily coalesces into something recognisable before dissolving again. People will define the scope of those objects through their definitions, but none is more valid than any other, it is just them imposing their paradigm on it.

              Identity in philosophy is defined by the logical premise 'X has all properties in common with Y', or 'X = Y'. It doesn't matter what a ship is or what defines a ship, as long as the same definition is applied consistently. It doesn't matter what you call X and Y, indeed X and Y themselves are just labels to make it easier to refer to the underlying entities.

              This isn't a great comparison, but perhaps think of it like the relationship between physics and maths. Physics is a high level way of expressing our observations of the way the universe works, while maths is the foundational concept that allows physics to be expressed. Physics strives to be as objective as possible but can be wrong, while maths is something of a universal concept that holds true no matter its language or expression. 2 + 2 always equals 4, whether we call it 'two' or 'zwei' or 'ni' or 'four' or 'vier' or 'shi'.

              Identity as a philosophical concept belongs to a level similar to the one at which maths resides. It's one of the fundamental notions of reality. Of course, in philosophy those notions can be questioned in ways that maths can't, but hopefully the comparison at least sheds some light on how philosophy regards concepts like identity in logical terms.

                I think you've lost me a bit sorry, bits of the conversation are slipping out the other side of my brain as this new stuff goes in... I think I need more RAM. :D

                So you're saying that identity is simply a consistently applied definition of an underlying entity. But are you saying that this definition exists without an observer to apply it?

                I not sure I personally believe that any philosophical concept belongs on a similar level to the fundamental nature of mathematics, especially if it's prone to paradox.

                  And therein lies the flaw with my comparison. They're not on the same level, but the relationship is more what I was trying to identify.

                  Identity does have to be consistently applied, but as a definition it's a unique one. For identity to be equal, all properties of X must be the same as Y, such that X = Y. The paradox and the debate comes from what constitutes the properties that make up X and Y, and to what extent they go. For example, two apparently identical white marbles, side by side, what property distinguishes the identity of one from the other? If the spatial location is a distinguishing factor, does that mean simply moving the left one to the exact position of the right one causes the left one to become the right one? It's an interesting question since we know there are two marbles and thus two different identities, but it's difficult to pose the correct properties that differ between them to cause the identities to differ. Certainly when acting upon the left marble, the right one doesn't move, so it can't be true that X = Y in this case.

                  Anyway, it's an unsolved problem in philosophy for a reason of course, and I'm certainly not saying you're right or wrong (but I'm always right *ahem*) but I find the discussion and debate of it fascinating nonetheless. Philosophy is great fun to indulge in.

                  As an aside, there are a lot of mathematical paradoxes. Have a look at Grandi's series and others.

                  @zombiejesus I really enjoy discussions like this, but I'm not versed in philosophy, so perhaps I'm questioning arguments that are already considered to be settled, sorry if that's the case! :)

                  I'm still not getting how an object has an identity fundamental to it and distinct from it's label, and as such I can't actually see a paradox here. I feel like a problem is being created where there is none. The difference between those two marbles, which are fundamentally identical, is that I call the one on the left "the left one" and the one on the right "the right one", and if you mix them up when I'm not looking it's irrelevant, which ever one is on the left is the left one. They have no identity beyond what I've assigned to them. If we fused the marble into mixture of atoms and extracted two identical marbles from them, each with a combination of material from the original two, it wouldn't be a problem because I still have "the left one" and "the right one". I don't think I'm able to get behind the idea that there is such a thing as a fundamental identity. You're defining what a fundamental identity is in philosophy, but to me it feels like a false definition that will only lead to problems and paradoxes.

                  Last edited 28/05/14 4:48 pm

        The simple answer to that is wherever the ghosts of the ship still haunt. Yes apparently Victory is Haunted by past sailors. It seems they know which is which!

    Nothing really stays the same anyway.

    Either the object changes; the perceiver and his perception of the object changes; or both entities change.

    well it is the same as the human body every few years all the atom that make up out body are replaced so are we still the same person. to the crew of a sailing ship it would be the same ship but the ship is just the name you give it. if bob gets his leg blown off by a cannonball and gets a wooden one does he no longer bob

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