# Ship of Theseus **URL:** \ **Category:** In My Humble Opinion\ **Created:** [March 27, 2010, 5:28am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998 "2010-03-27T05:28:49Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 27, 2010, 5:28am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/1 "2010-03-27T05:28:49Z")
[Ship of Theseus](http://en.wikipedia.org/wiki/Ship_of_Theseus) > [@Plutarch](#): > > The ship wherein Theseus and the youth of Athens returned [from Crete] had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same. > Plutarch thus questions whether the ship would remain the same if it were entirely replaced, piece by piece. Centuries later, the philosopher Thomas Hobbes introduced a further puzzle, wondering: what would happen if the original planks were gathered up after they were replaced, and used to build a second ship. Which ship, if either, is the original Ship of Theseus? Hobbes’s question intrigues me. It seems to me that as parts are being replaced, the refurbished ship is the ‘original’ one. But if all of the original parts could be collected and put back together, then _that_ must be the original ship. At what point does the refurbished ship stop being the ‘original’ ship and the original parts become, once again, the original? Or consider a car. I have a '66 MGB. As it happens, MGB bodies are still being made. One could refurbish or replace all of the parts of an original-bodied MGB and put them onto/into a new body. Is it still the same car? The dataplate says it is. (NB: In my case the body is original, but the front fenders and bottom halves of he rear ones are OEM replacements.) Or how about a really extreme example? In an aircraft, you could say that the dataplate is the aircraft. There’s a woman in England who built an exact copy of a Spitfire in her garage. Suppose she had an actual, original dataplate? Would her plane become _that_ plane? Would it matter if she had the dataplate before she started? Would she have to have the wreckage of the original plane (plus the dataplate) to make a ‘repaired’ airplane made entirely of newly-made parts the ‘original’ plane? If so, then how much? Then there’s ‘George Washington’s Axe’, which was mentioned in a Cafe thread, and which prompted this one. This is probably the simplest example, since there are only two parts. ISTM that once both parts have been replaced, it ceases to be George Washington’s axe. So why would a ship or a car or a plane be any different? And yet, they are in some way. ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [March 27, 2010, 5:45am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/2 "2010-03-27T05:45:00Z")
Plus the more immediate problem - if I eat food, and replace parts of my body with the atoms and molecules derived from the food, ultimately replacing all of them, am I still me? Buddhist philosophy argues that all things are aggregates ([skandhas](http://en.wikipedia.org/wiki/Skandha)) of other bits, and that therefore nothing is permanent. From that perspective, the ship is as much itself after its bits have been replaced as it ever was. . ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 27, 2010, 5:48am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/3 "2010-03-27T05:48:14Z")
> [@Attack\_from\_the\_3rd\_dimension](#): > > Plus the more immediate problem - if I eat food, and replace parts of my body with the atoms and molecules derived from the food, ultimately replacing all of them, am I still me? Though the atoms are replaced, the mind remains. > [@Attack\_from\_the\_3rd\_dimension](#): > > From that perspective, the ship is as much itself after its bits have been replaced as it ever was. What about Hobbes’s question about using the original, discarded parts to build another ship? ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [March 27, 2010, 6:52am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/4 "2010-03-27T06:52:22Z")
> [@Johnny\_L.A](#): > > Though the atoms are replaced, the mind remains. Which brings us to the mind/body problem - all of philosophy, soon to be covered in a single thread. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [March 27, 2010, 7:45am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/5 "2010-03-27T07:45:18Z")
> [@Johnny\_L.A](#): > > Though the atoms are replaced, the mind remains. But it does not remain the same: knowledge grows, memory changes, illness destroys. On one hand, I’m the same person that was photographed in my grandfather’s arms in 1971; on the other, there are things that little girl could do and I can not, and others I can do and she could not. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [March 27, 2010, 9:24am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/6 "2010-03-27T09:24:00Z")
> [@Johnny\_L.A](#): > > Though the atoms are replaced, the mind remains. > What about Hobbes’s question about using the original, discarded parts to build another ship? When greater than 50% of the original parts have been replaced, it is no longer the original ship. If all the original parts of the ship are saved and reassembled, it will be the original ship, and will promptly sink from all the rot holes. You’re welcome! 😛 ---
**Author:** ![nachtmusick](https://avatars.discourse-cdn.com/v4/letter/n/ac91a4/32.png) [@nachtmusick](https://boards.straightdope.com/u/nachtmusick)\ **Post date:** [March 27, 2010, 11:49am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/7 "2010-03-27T11:49:19Z")
Related quandary: Death by Science Fiction Teleporter. When Captain Kirk beamed down to the planet, the teleporter presumably scrambled his atoms and then re-assembled them on the planet surface. The laws of physics preclude that the actual substance of his body could be transported in that fashion, so we must conclude that the transporter dis-assembled him, beamed the information to the planet at light-speed, then the planet’s transporter re-assembled him. The Kirk that walks off the platform on the planet is identical to the Kirk that was beamed from the Enterprise in every sense, and even remembers stepping into the Enterprise’s transporter. But he is formed of different atoms. If the original Kirk died on the transporter deck of the Enterprise when the transporter dis-assembled him, how would any outside observer be able to tell the difference? ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [March 27, 2010, 1:07pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/8 "2010-03-27T13:07:37Z")
If a rotting plank is removed from the ship and replaced with new lumber then the rest of the ship is original and that plank is a reconstruction. As the number of planks increases the more parts of the ship are reconstructed. When all the planks have been replaced it is no longer the ship but a reconstruction. A ship made from the original planks is a reconstruction from original materials. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [March 27, 2010, 1:54pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/9 "2010-03-27T13:54:46Z")
> [@Johnny\_L.A](#): > > Though the atoms are replaced, the mind remains. What happens when you change your mind? 😛 ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [March 27, 2010, 3:53pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/10 "2010-03-27T15:53:42Z")
> [@nachtmusick](#): > > Related quandary: > > Death by Science Fiction Teleporter. > > When Captain Kirk beamed down to the planet, the teleporter presumably scrambled his atoms and then re-assembled them on the planet surface. The laws of physics preclude that the actual substance of his body could be transported in that fashion, so we must conclude that the transporter dis-assembled him, beamed the information to the planet at light-speed, then the planet’s transporter re-assembled him. > > The Kirk that walks off the platform on the planet is identical to the Kirk that was beamed from the Enterprise in every sense, and even remembers stepping into the Enterprise’s transporter. But he is formed of different atoms. > > If the original Kirk died on the transporter deck of the Enterprise when the transporter dis-assembled him, how would any outside observer be able to tell the difference? You need to learn to think like a dinosaur. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 27, 2010, 5:21pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/11 "2010-03-27T17:21:06Z")
> [@Nava](#): > > But it does not remain the same: knowledge grows, memory changes, illness destroys. On one hand, I’m the same person that was photographed in my grandfather’s arms in 1971; on the other, there are things that little girl could do and I can not, and others I can do and she could not. I knew when I wrote that that someone would mention growth and change. I’ve said that a murderer about to be put to death is sometimes ‘not the same person who committed the crime’. I was hoping that people would understand that I meant that a person’s mind changes, but it is still the same mind. That was lazy of me. What I was trying to say is that even though the cells that make us up are only a few years old, though we are decades old, we are still us. There is a continuity in living things that makes them the same even though their structures have been completely replaced. But does this continuity apply to inanimate objects? **Boyo Jim** makes a reasonable point that when more than half of something is made up of replacement parts, it is no longer the same. But if the replacement parts are added gradually over time, then the thing itself (i.e., the sum of its parts) is still ‘original’. At least up to a point. Take the car, for example. Parts are expected to wear out and need replacement. In reality, no one replaces _every_ part in a car. Though my MG is virtually new. I was hoping to avoid this, but I’ll have to use my car here. It was a wreck when I got it. There was considerable rust, and sheet metal parts were replaced with sheet metal made on the original factory equipment by a Trust set up to provide OEM parts. Is it ‘original’, or isn’t it? Since auto repair has been a part of automobiles since their inception, and since OEM parts were used, it is as original as it would be had it been in a wreck a day after it left the factory and was repaired 44 years ago; much like I am still me, even though all of my ‘parts’ have been replaced or the Ship of Theseus was itself even though it had been repaired. When I got the car, it had a non-overdrive transmission. But the engine’s serial number indicated the car was originally equipped with an overdrive transmission. I bought a rebuilt o/d transmission for it. Since the transmission is not the one it left the factory with, I am not comfortable calling it _factory_-original; but I am comfortable calling it ‘original’ since the transmission is from the factory and is correct for this car. Accessories, trim, and sheet metal are expected to be replaced whether the car is a day old or in its fifth decade, so a car that has been maintained is still ‘original’. Replacing an entire transmission is a bit of a stretch, but it’s still an accepted repair. A further tangent: Airplane engines need to be overhauled periodically. Rather than rebuilding the engine that was mounted on the firewall when the aircraft came off the line, it is common to install a new, rebuilt, or ‘zero-time’ engine and send the original engine away to be rebuilt and used in someone else’s aircraft. (A new engine is one that is new from the factory. A rebuilt engine is one that is used, but has been rebuilt to specifications. These are ‘0 SMOH’ – ‘zero time since major overhaul’. A zero-time engine is one that is used, but is factory-remanufactured and is issued a new logbook.) Again, engine swaps have been an accepted maintenance procedure since there were airplanes, and thus do not affect ‘originality’. So the Ship of Theseus, or a car, or a plane, or what-have-you is still ‘original’ even though repairs have been made and maintenance has been done. I don’t see a problem with this. Maintenance and repairs are ‘parts’ that are part of the history of the thing just as one’s ‘self’ is a part of a person even though none of the atoms in his body are the ones he was born with. Where this breaks down for me is when you have a stack of parts that have been replaced. As parts, they are just the original parts and the thing itself is still original; albeit repaired. But to assume the extreme case of total replacement, and the original parts reconstructed, that presents a problem. Legally the airplane with 100% replaced parts is the original because of its history of starting from the original and because it has the dataplate. But the original parts reconstructed are ‘really’ the original. Or is it? The airworthy airplane (or other thing) has the fourth-dimensional ‘heritage’ going for it. The reconstructed parts are just reconstructed parts that cannot serve the purpose for which they were originally assembled. (Unless, of course, repairs are made and non-functional parts are discarded and replaced…) ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [March 27, 2010, 8:59pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/12 "2010-03-27T20:59:26Z")
Kind of heard this one as a kid at camp. This is George Washington’s (or Abe Lincoln’s) Axe. Sure, we’ve replaced the handle three times and the head twice… ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [March 27, 2010, 9:00pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/13 "2010-03-27T21:00:21Z")
> [@nachtmusick](#): > > Related quandary: > rs stepping into the Enterprise’s transporter. But he is formed of different atoms. > > If the original Kirk died on the transporter deck of the Enterprise when the transporter dis-assembled him, how would any outside observer be able to tell the difference? I’m a doctor, not a stream of quantum waveforms, dammit. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [March 27, 2010, 9:54pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/14 "2010-03-27T21:54:30Z")
You mentioned planes, but for them there’s an answer: The data plate. Legally you really can replace everything else and it will still be the same plane. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [March 27, 2010, 10:48pm UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/15 "2010-03-27T22:48:53Z")
> [@ElvisL1ves](#): > > You mentioned planes, but for them there’s an answer: The data plate. Legally you really can replace everything else and it will still be the same plane. Yes, I mentioned that here: > [@](#): > > In an aircraft, you could say that the dataplate is the aircraft. Do let’s say this English woman had a data plate from an original Spitfire and applied it to the one she built from scratch. Legally, in the U.S., that would make hers the ‘original’ one. But suppose there was a pile of wreckage that the dataplate came from, and those bits were reassembled. (Of course bring wrecked, it would not be flyable.) Legally, since the dataplate is on the scratch-built aircraft, it doesn’t exist. But it does. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [March 29, 2010, 3:35am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/16 "2010-03-29T03:35:47Z")
> [@Inner\_Stickler](#): > > If a rotting plank is removed from the ship and replaced with new lumber then the rest of the ship is original and that plank is a reconstruction. So let’s say the ship had a working life of 30 years, and at year 15 the rotting plank was removed and replaced. 200 years later would you say that the ship is mostly orginal “except for one plank which is a reconstruction?” ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [March 29, 2010, 4:12am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/17 "2010-03-29T04:12:45Z")
It would be a very odd ship that only needed one plank replaced over the course of 30 years. I wouldn’t consider it a reconstruction until the ship has been removed from duty and relegated to a historical piece. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [March 29, 2010, 4:31am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/18 "2010-03-29T04:31:08Z")
None of the original members of Thin Lizzy are still in the band, but they continue to perform as Thin Lizzy. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [March 29, 2010, 5:20am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/19 "2010-03-29T05:20:36Z")
Similarly, there are no remaining original ships OR men of the US Navy, but still they continue to call themselves that. 😛 ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [March 29, 2010, 7:37am UTC](https://boards.straightdope.com/t/ship-of-theseus/533998/20 "2010-03-29T07:37:12Z")
> [@](#): > > Do let’s say this English woman had a data plate from an original Spitfire and applied it to the one she built from scratch. Legally, in the U.S., that would make hers the ‘original’ one. But suppose there was a pile of wreckage that the dataplate came from, and those bits were reassembled. (Of course bring wrecked, it would not be flyable.) Legally, since the dataplate is on the scratch-built aircraft, it doesn’t exist. But it does. I did something similar to this at work once. We wanted to get a new computer in our office. We found a cheap one and asked if we could bring it in. We were told no because bringing in any outside computers required approval from way up high. And all of the equipment had little tags on it to show that they had been authorized. Now there was a room where we stored out out-of-date equipment, including old computers. So we asked if we could have one of these old computers that was already authorized to be there. We were told that would be okay. Then we said that many of them needed repairs so could we bring in some parts to repair them. So we were given permission to bring in “parts” to repair one of the old computers. So we took an old computer with its authorization tag. Then we removed the old computer from the authorization tage. Then we brought in the “part” which was the outside computer and attached it to the authorization tag. And after that, sure enough, that “old” computer worked just like a new one. [Next page](https://boards.straightdope.com/t/ship-of-theseus/533998.md?page=2)