[InsaneBaron]

So I've been studying Metaphysics lately. It's fun! Recently we tackled a very interesting question:

In ancient times, Theseus built a ship he used to defend Athens. After Theseus died, the Athenians decided to preserve his ship as a memorial. But after a time, a few of the planks started to rot, so the Athenians removed them and replaced them with fresh ones. A few years later, more planks started to rot and were replaced. This continued for centuries, until one day every plank of the ship had been replaced- there wasn't a single original plank left! Is it still the same ship Theseus used? If not, when did it stop being Theseus's ship?



For an added twist, suppose the old, partly-rotted planks were not discarded, but stored in a museum. Then, after every single plank has been replaced, someone takes all the rotted planks and puts them back together to form a ship. So now you have two ships. Which one is the ship of Theseus?

Who wants to try and answer? I myself am stumped.

[Flipside]

'This is the axe of my Grandfather, sometimes it needs a new handle, sometimes it needs a new blade, but in every way, it is still the axe of my Grandfather'

- Terry Pratchett

[InsaneBaron]

'This is the axe of my Grandfather, sometimes it needs a new handle, sometimes it needs a new blade, but in every way, it is still the axe of my Grandfather'

- Terry Pratchett

Pretty much.

[AdmiralRalwood]

Is it still the same ship Theseus used?

Yes.

Which one is the ship of Theseus?

The non-rotted one.

[Mars]

This applies to living things as well, since every cell in an organism gets replaced rather rapidly. The concept of a tool, ship, or person, and its design or genetics of it is the more durable part.

[Lorric]

Nice thread. Reading the OP had me confused too, but I have to agree with the other posters, great points made by Flipside and Mars. And of course the Athenians would certainly see the ship as the Ship of Theseus too.

[InsaneBaron]

This applies to living things as well, since every cell in an organism gets replaced rather rapidly. The concept of a tool, ship, or person, and its design or genetics of it is the more durable part.

In other words, (Aristotle's to be exact), you're saying the "form" is more relevant than the "matter" that makes it up. I agree it's pretty clearly the case with living creatures; so it's reasonable to apply the same logic to artificial objects.

To play devil's advocate, the "rotted" ship has all of the original parts of Theseus's ship, arranged in the same positions as the original- basically, the ship was dismantled and then put back together. That would make the non-rotted ship a high-quality replica.

Or maybe there's a third way; perhaps it's not a yes-or-no question, but a matter of degree? Perhaps the ship becomes less and less "Theseus's ship" over time.

Good points all around, guys!

[Scourge of Ages]

I asked myself this the last time I build a computer: When does an upgrade become an entirely new machine?

If you format the hard drive, it's still the same computer.
If you replace the hard drive completely, it's still the same machine.
If you replace the motherboard and CPU, it's still the same machine.
If you replace the case, it's still the same machine.
What if you do all of those at once?

I say, each person decides for themselves.
Personally, I say the functional one remains the primary ship/body/machine, as long as a significant portion of the old one remained at the time of change.

[Flipside]

I think it's something to do with time, if the handle and blade of 'my grandfathers axe' break at the same time, only then is the axe destroyed, as it were.

[Dragon]

I think that in this case, the rebuilt ship would be the Theseus' Ship. The other one becomes a replica (though a good one) the moment the last original timber is removed. To be considered the original, if restored, vessel, it should have at least one original part from the old one. For somewhat more modern ships at least, it's usually the ship's bell and the figurehead, maybe the nameplate (if the name isn't just painted on the timbers). Same with the axe, it's not "grandfather's" anymore if you replace both the handle and the head at some point after he died. However, it's easy to be fooled into thinking it is, because it'd be a deceptively accurate replica (Discworld is a bit different, since what you believe comes true fairly easily there, so this question is much easier).

If you replace the motherboard and CPU, it's still the same machine.

Actually, it's likely the point where it ceases to be the same machine. To replacing the motherboard and CPU often means reinstalling the OS and that, in turn, means you lose your HD contents, or at least installed programs (or else have to transfer them somehow). Unless you do some trickery to avoid starting from scratch like that (I had a mobo replaced with a slightly newer one from the same series, and had painlessly upgraded from Vista to 7, but those are special cases), replacement of the CPU+mobo+OS is usually enough to call it a new computer.

[Aesaar]

The parts of an assembly carry no information about the assembly itself.  If the ship itself was never destroyed, then at no point did it stop being the same ship.  As long as the assembly itself continues, its components don't matter.

Dragon: what if I replaced the CPU and Motherboard with identical ones?

Here's another question: if I duplicated a computer down to every single atom so that every component, every speck of dust, every electrical charge were completely identical, then destroyed the original at exactly the same time, why wouldn't it be the same computer?

[Lorric]

It's a fun little problem to chew over, isn't it. I'm not sure if there is a right and wrong answer to this. Your Ship of Theseus with the rotting wood would be the ship built from its original components (if it could still hold together at all), but your restored ship would be a better representation of what the ship looked like when it was in service than the rotten wood ship, and would have been a series of repairs on the original ship. The intangibles are what makes this difficult I think. Whether something is still something in spirit even if not of its original components.

[InsaneBaron]

Here's another question: if I duplicated a computer down to every single atom so that every component, every speck of dust, every electrical charge were completely identical, then destroyed the original at exactly the same time, why wouldn't it be the same computer?

Because, while the parts are identical, they aren't the same parts

[Herra Tohtori]

while the parts are identical, they aren't the same parts

What about quantum teleportation?

Do atoms and elemental particles have individuality?

[deathfun]

Taking a different spin on what Flipside said, it's the concept, or the idea of the something that belongs to someone
In the case of the ship, his ship was seaworthy and that particular design was the one he used. The rotted parts are yes, the wood from the original, but the ship that's seaworthy is closer to being the original than the rotted one. It's called restoration

Look towards any sort of monument anywhere, Italy will be my example. Constantly, places are being restored and fixed in order to maintain their structural integrity. Are these places any less than that they were before? As far as any tourist is concerned, nope

Another way to look at it is that the Ship of Theseus is a name, not a notion of direct possession.


So to answer the question (and effectively conclusion), it asked, is it the same ship that he used? No, that'd be impossible for it to be the exact same ship he used as the ship he used had planks made from long ago. However, that does not mean it ceased to be the Ship of Theseus as the Ship of Theseus is an idea, memory, concept, and the physical is just a representation of that idea.

For me, the question makes it seems too one or the other. The first line being, is it the same ship that he used? If you say no, then it immediately moves you into the position of "when did it cease to be". I dislike this because it never ceased to be his ship, it just ceased to be his precise ship that he used.




Now here's where it becomes even more involved. What makes the object itself unique? I have a Mosin Nagant used from WWII. It carries with it the history, the grime, and the dings dents and damage from seventy years ago (with cleanings there and here but the scratches remain). Now while the gun's design on its own carries an overall history, the individual gun tells a story too. If I repair the damages, replace the bore and overall make it as though it just came off the factory line, I in turn destroy the history involved in that one rifle itself. I still have my Mosin, but given what made it unique out of millions is what those pieces and parts went through, I have effectively removed the personal history of the gun. Its overall history remains, but the individual history does not.

[AdmiralRalwood]

I think that in this case, the rebuilt ship would be the Theseus' Ship. The other one becomes a replica (though a good one) the moment the last original timber is removed. To be considered the original, if restored, vessel, it should have at least one original part from the old one.

By this logic, you are merely a clone of the original Dragon.

[An4ximandros]

We are all mere vessels to something greater, something that cannot die: Ideas. Stories. Symbols. Memes.

[Dragon]

Basically, personality and memories. It's the former makes you a human you are. The latter are important, but secondary, in that you can forget anything and still be the same person.

By this logic, you are merely a clone of the original Dragon.

Materially, yes. My body is not made of the same particles it was years ago and I don't make a fuss about it. It currently doesn't even look much like what came out of my mother. However, there is something more to a living being: the personality stored in the brain. This is why I don't oppose concepts like brain transplants and so. As long as the brain, and the underlying personality is intact, the everything else is secondary and can (and should, if the need arises) be replaced. Humans, unlike axes (but not unlike ships and computers), have a "soul", or at least a personality, the preservation of which is more important than that of the material vessel. Indeed, the material vessel and personality are two different entities. It's the latter that really is "the" human being in question, it's also what goes away after death (the body might still be perfectly good). It can't exist without some vessel (much like OS data has to be written on something), but as long as a sufficient one is provided, it's mostly irrelevant what exactly it is.

Dragon: what if I replaced the CPU and Motherboard with identical ones?

Then you could argue either way, but I think it'd still be an upgrade, basing on what I said above about humans. The OS "setup" is what matters here. If you reinstall the OS and lose the data (or at least have to adapt it due to registry stuff changing), then it might be considered a "new" computer, even if the parameters are the same as before, because you changed the "personality" (if you've used the thing for long enough, you can leave off the quotes ). On the other hand, if you don't have to do that, you're still using the old computer, though physically, the machine may be new (as in, the parts would have warranty again).

It's harder to say where the "soul" of the ship is. Every ship, especially a sailing one, has its own little quirks and characteristics (in my country, at least, you're required to have experience as a first officer on a 20m+ ship for some time before becoming its captain, on top of needing to have the papers). They certainly do not reside in traditional ship's artifacts, such as the bell and the figurehead, so it's pretty hard to pin down. The ship made of rotten timbers would likely be unseaworthy (so it'd be hard to tell whether it's still sailing like it used to), but the replica's characteristics might change slowly over time as parts are replaced (especially if they're not replaced with perfectly the same kind of materials). I guess I haven't sailed nearly enough to be really able to tell, you might want to ask an actual sea wolf, not a beginner like me.

[karajorma]

To be considered the original, if restored, vessel, it should have at least one original part from the old one.

Okay then, is it still the Ship of Theseus if you probably still have original planks on board but maybe have already replaced them all?

[Aesaar]

Here's another question: if I duplicated a computer down to every single atom so that every component, every speck of dust, every electrical charge were completely identical, then destroyed the original at exactly the same time, why wouldn't it be the same computer?

Because, while the parts are identical, they aren't the same parts

What makes them different?  The atoms that make it up carry absolutely no information about what it is they're constituting, so what is it that makes these two hypothetical computers different?