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Ship of Theseus (wikipedia.org)
46 points by BudVVeezer on Aug 19, 2015 | hide | past | favorite | 50 comments

A thing's identity doesn't reside in the object itself, but rather the person or persons doing the identifying. Also, identity can be split into elements. The name, as in "Ship of Theseus," can be swapped out independently of the elements, though doing so tends to lead to confusion.

The example given of the sock with the hole in it: assume it's the only sock that the owner has with that hole. If the hole goes away, then it no longer has a unique identity, it's just another sock in his drawer. What gave it an identity in the first place was the fact that it was different.

With a ship, its identity appears to be tied to its designation. If you carried on replacing all the parts of the ship, it'd still be the Ship of Theseus, because that's what it's called. Back in the day when I owned a desktop computer, several times this would actually happen. Every component would got swapped out over a period of time. It carried on being my computer throughout all of it.

A computer's identity can be arguably split into two main elements, a computer and a system. If I replace the operating system and wipe all the data, using it feels completely different. Yet it's the same computer, just running different software. If you replaced the crew of a ship with a different crew, then the ship would operate differently, say, in battle, but it would still be the same ship.

You could restore the old system / crew and retrieve the original functionality, but if you replaced both the hardware and the 'software', yet kept the designation, you have two different things with the same name.

A person's body has all of its cells replaced after a period of years. But we don't go around emptying the prisons of long-serving inmates on the basis that the person that committed the crime isn't the same as the person currently in jail.

One can devise conceptions of identity with varying degrees of immutability. The conundrum makes the incorrect assumption that identity itself is an immutable concept. It's not.

What I find more intriguing in this article is that whenever I click in the "Śūnyatā" reference link (by the end of the page) it moves to the column on the right side.

Would that be the same link or is it a new one?

For a somewhat practical example of such a ship:

"The detachment estimates that approximately 10–15 percent of the timber in Constitution contains original material installed during her initial construction period in the years 1795–1797"


There's a wonderful Indian film with the same name which kind of touches on the subject - https://en.wikipedia.org/wiki/Ship_of_Theseus_(film)

I would recommend the movie to the fans of cinema/indie movies.

Where this question becomes practical is with the Origination clause of the US constitution. It states that any bill for raising revenue must originate in the House of Representatives. If the House passes a bill that deals with some topic, and then the Senate amends it by removing all of its' language and replacing that language with something else, did that bill still originate in the House?

See: Sissel v. United States Department of Health & Human Services

Thanks for posting this. I was about to check out as this being a bit of philosophy I have no interest in. But, I can see where at least having a name for the phenomenon makes since in circumstances like this.

Works well for code projects too! Is it the same code base, even if all the lines are rewritten?


Graydon Hoare about what code he has left in Rust.

The answer to this may have a serious impact upon whether my github account is full of awesome code examples that I wrote myself.

I think of it like a band (Could well apply to a company too) which occasionally replaces members. So long as they replace few enough members each time that people can associate it with its previous roster, people will accept it as the same band.

Even if after 20 years of incremental changes to the band none of the original members are left it will still be considered by many to be the same band (although they will all likely lament the loss of such and such member) By being recognized as the same band it inherits many of the same rights such as performing the same songs as the previous incarnations of the band (assuming of course it owns, or pays royalties to the right holders, but that is an unrelated topic).

However if too many members change at once, or they lose a member whose presence independently defined the band then people will likely not consider it the same band.

The identity is a label applied to the set, as the set changes so does the definition of the label. For the most part assuming members of the original set do not get placed in different new sets all identifying as the original label, people will generally accept the label as applying to the new set which was formed.

I would chalk it up to people being stupid, or language being imprecise. The alternative seems to be to consider every change to the set to require a new label and be identified as a new set.

The Wikipedia article mentions a band, the Sugababes, that started with three founding members, but one by one all of them ended up leaving the band and being replaced. Is it still the same band?

An interesting twist is that the three founding members regrouped and formed a new band, with the Sugababes still in existence. Which is the real Sugababes?

A band isn't only defined by its members, though. They can have a distinct sound, a preferred genre, even various brandings and styles that make for a markedly different performance.

But those attributes are defined by the members. :)

Not really. For bands like the Sugarbabes they are defined by the producers, session musicians, composers and lyricists.

But those members may choose a different set of attributes to build a different band brand.

> Could well apply to a company too

I've thought about this in the past. Companies get a reputation for doing certain things poorly or doing them well. For example, think of high profile games from a long time ago that have continued to release new versions to this day. How many of the people who worked on v1 have continued to work on the latest release?

On a larger scale, consider what happens when the oldest person in the world dies. Every person born before them is gone. How did we manage to perpetuate all of the ideas, culture and values through to an entirely new set of people? The mechanics are easily observable, but the scale is boggling.

This gets very interesting in terms of long-lived companies. Should we boycott, say, IBM for aiding the Holocaust? Even if no one in the management is alive or working for the company anymore? Hard to say. It's still the same company, but run by different people.

Another great example of this is a sports franchise.

The St Louis Rams have different ownership, players, coaches, and city from the LA Rams. Are they the same team?

In sports, every year something small enough changes to make people accept that it is the same team.

In order to experience/measure something, you must interact with it. Any interaction changes both sides. You can't experience the same ship twice.

That's not really satisfying on a human level, though. I can't take your car and claim that it's no longer "your" car since some atoms changed.

To generalize, physical identity seems to be an important part of ownership, so how does that interact with this concept?

Just accept unsatisfying, impractical truths, and despite that, allow yourself to have an illogical intuitionistic sense of things. That's what I do. :)

I love this insight. Thank you.

Also thank Heraclitus (535 B.C) -- which goes even further: even time changes things, so you can't experience the same ship twice even without interacting with it.

Known a bit more prosaically as Trigger's Broom in the UK.

And applies to humans, too, with our continually regenerating cells.

There's a good conversation about this, humans and cell regeneration specifically, in the movie "Waking Life" (as well as many many other great conversations about a variety of philosophies)

Is that the animated movie about dreams from ~10yrs or so back?

yes, the fact that it applies to people makes it very interesting.

am i the same person as when i was born?

i would like to think that i am... but 'knowing' this makes me question a lot of the seemingly obvious things about self, to the point where i wonder exactly what i am, and realise that it is very poorly defined to start with... and probably not so special. :)

also... Trigger's broom is classic. :)

There is no you, yet there you are.

The DMV solves this by saying, "The Frame".

Now I don't know what happens if I cut out the left frame rail and replace it, then cut out the right rail and replace that, then the front sub-frame, then the rear. Whichever section has a VIN plate riveted to it??

Similarly, the ATF solves this by saying "the lower receiver".

i would guess that you are actually not allowed to do such work, that is kind of the point... at least here (UK), to be legal i'm pretty sure you need to get a DVSA (used to be VOSA) inspection and approval rather than just a regular MOT if you do work like that.

although the regulations in the US are famously lax compared to the rest of the developed world... so maybe there is just nothing there. XD

It reminds me about the story of a famous Japanese street food vendor, who had cooked soup out of the same pot for fifty years, every day, never stopping to clean the pot, because he never stopped cooking soup out of it. When the soup got low, he just threw in the ingredients it needed to fill the pot again. According to the story, he had been serving the same pot of soup for fifty years. Pardon if I have murdered this story, and I have no idea where it comes from. Just something I read one time, and remembered.

In USA: "marry ketchup bottles"


The answer depends on perspective and subjectivity. If I took the ship across the ocean last year, and now I take the fully-parts-replaced version this year, I'm still calling it by the same name. In my mind it is "same", unless I decide to get especially academic about it. It is both same and not-same. Meh. Not the most interesting of paradoxes. ;)

Its more interesting when you consider how it applies to living beings. If I replace every part of a dog with cybernetics, is it still the same dog? At what point does it stop being the same dog? The brain? The nervous system? Other various senses? How much of identity is tied up in how a creature perceives its environment? What happens to the creature when we alter that perception or enhance it?

is identity even real? such thinking can be construed as a 'reductio ad absurdum' argument that it is not...

how can we even tell if it is a concrete concept? its very poorly defined to begin with too...

I'd guess it's about as real as most other concepts we use - fuzzy at the borders and breaking down when you focus on them too hard. It's like asking when a chair stops being a chair - when it has 3 legs? 2 legs? When it's angled 45 degrees? 30 degrees? Etc.

I suspect that identity is just another way of grouping things by properties, in this case including sharing spatial and temporal history - I am the same I was 10 minutes ago, because I'm made mostly of what I was made 10 minutes ago, and I moved somewhat continuously through space, etc.

yeah, it falls out of how the brain functions i think... there are a bunch of classifiers in there, and its not always easy to map what they do to reasoning. there are loads of fuzzy concepts like this with day-to-day utility which are very difficult to define accurately in a way that unambiguously communicates intent to another person.

> The answer depends on perspective and subjectivity.

And therein lies the entire discipline of Philosophy.

As Paul Graham pointed out in his essay on philosophy, it depends on your definitions. Here, it depends on your definition of "same". But that makes it a much less interesting discussion about different (mostly unstated) definitions of the word "same", rather than a profound philosophical discussion about something...

No, it's obviously still a profound philosophical discussion about identity.

Saying "it depends on your definitions" sidesteps the whole issue of how you come to these definitions, and what impact they have on how we view reality. In other words, it hides the profound issues under the rug.

For example, a common argument against moving your brain information to a robot as a way to "live forever", is that then it's no longer you (since your physical brain ceazes to live).

The Ship of Theseus sidesteps this argument, since an example of it would be replacing your neurons one by one with artificial ones -- with you awake.

With such a procedure, you feel exactly the same at all times, and you have no recourse to saying your personality was merely "transfered".

It feels like you were the physical person X, and after these steps, you were the same person with a robotic brain, but with no abrapt change or loss of consciousness, just a continuous process.

All right, let me put it this way: There may be a profound philosophical question about identity. However, because of the problems of the differing, unstated definitions of "same", almost all of the discussion is really about the assumed definitions of words, and is therefore almost completely a waste of time. It appears to be about the profound philosophical question, but it's mostly not.

It still is profound whatever one's definition of same. Pick a definition of same. Make it as precise as you want. It might be totally compatible with some of those definitions you come up with. For all others, The Ship Of Theseus still makes a powerful questioning tool that raises insights to question those "single, precise" definitions.

There's a naive (mostly anglosaxon/empiricist) idea that philosophy is just noise because of the conflicting definitions of things.

Whereas it's the total opposite: questioning and disecting the definitions we use (and what they presuppose), is the exact role of philosophy.

The Ship of Theseus (and countless others ideas and paradoxes) are tools in questioning those beliefs and "definitions".

Those examples don't stem because of our confusion about what is same -- they are tools to probe what we consider same, to poke holes in our idea of sameness.

And I call the objection to this naive, because having a "single objective definition" is not something possible (like science doesn't claim to know some ultimate "reality", just to make ever better models and approximations of it).

We have to live with various ideas about identity/sameness, and we need philosophy and arguments like The Ship, to question them and see their partial nature.

I don't think there's a "single objective definition". There are multiple valid definitions. What I'm saying is that most of the discussion about The Ship Of Theseus is really discussions about the definition of "same", but most of the time, people don't realize that that's what they're arguing about. This means that most of the argument is wasted time.

Sure, have a discussion about different definitions of sameness. (Ironic, that.) Poke holes in the various definitions. That's fine. Just don't have conversations where two different people have different implicit definitions of sameness, and each sees the other's position as clearly stupid, because the other person is using an unstated, but different, definition of "same".

>Just don't have conversations where two different people have different implicit definitions of sameness, and each sees the other's position as clearly stupid, because the other person is using an unstated, but different, definition of "same"

As you say, discussing X while having 2 different ideas of X is obviously wrong -- people practically talking past each other.

But that's only if the discussion is not philosophical but just a practical, everyday conversation.

That's because in the latter people talk and talk about X while X goes unexamined, where the essense of a philosophical conversation is to examine X, and investigation how each one defines it, and what might be correct or wrong about any singular definition.

A non-philosophical discussion would be: - X song is the same as Y, they stole it. - No it's not, they just have the same chord changes. - They should come out with their own, they're copycats.

Whereas a philosophical disussion would be in the vein of: "what is sameness?" (itself), "when we can say that a song is stolen from another?" etc.

The best enunciation of this was the opening scene of John Dies At The End: https://www.youtube.com/watch?v=O-W_P7rMQRA

It has been said that every cell in your body is replaced every 7 to 10 years. This is not actually true, since brain cells aren't replaced but if it was, we would all be "Ships of Theseus".

Is the ship a reference object or a value object?

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