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.

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"

https://en.wikipedia.org/wiki/USS_Constitution

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

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

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.

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

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

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

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??

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.

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. ;)

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...

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?

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?

> 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.

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.