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Theseus' Ship Paradox

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Trigger: This ol' broom... has had 17 heads and 14 new handles in its time.
Sid: How the 'ell can it be the same bloody broom, then?
Trigger: Well, 'ere's a picture of it; what more proof do you need?

The Ship of Theseus is a classic philosophical thought experiment about the nature of identity. Is a thing simply the sum of the specific parts that compose it? And if those parts are gradually replaced, is it still the same thing?


The classic story goes as follows: Theseus sails the world on his famous ship, but as the pieces of the ship begin to wear down, he replaces them. By the time his voyage is finished, every single part of the ship has been replaced. So is the ship at voyage's end still the same ship that first set sail? Another version holds that, after sailing the world on his ship, Theseus docks it and keeps it in working order by gradually replacing all of its pieces. Someone else buys all the pieces that Theseus discards and assembles a second ship from them. So which is the ship that sailed the world? The one in Theseus's dock, or the one built of all the pieces of the original ship?

Or for a more consice example, if you have a hammer and the head breaks, you replace it. But if later on the handle breaks, you'd have to replace that as well. But would it be the same hammer anymore?


Examples of the conundrum in fiction can play out with virtually any object. A common alternative to is the "Grandfather's Axe" story. The trope gets a lot of play in science fiction when we consider whether Cybernetics Eat Your Soul. If you replace parts of your body with machines, are you still really you?

Compare with Soulless Shell.


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  • An old toothpaste commercial shows a futuristic apartment with a guy who claims that his grandmother still uses the same toothpaste and that her teeth are the only parts of her that are original. Cue a stunning young blonde passing him with the guy giving her a "Hey, Grandma!" The ad was shown at a Russian game show, and the team was asked to figure out what was unlikely about it. Naturally, they focused on this trope, arguing that it's impossible that a person could have nothing original except her teeth. The real answer was that the tooth shown in the ad had four roots, which is extremely unlikely (many viewers agree that the team should've been given that point).

    Anime and Manga 
  • This gets addressed in One Piece when the Straw Hats are hoping to repair their ship, the Going Merry. Because the keel (essentially the backbone of any ship) is severely cracked, the ship is declared irreparable. When Luffy suggests they just build a "new Going Merry", it's pointed out that even if the shipwrights built a new ship precisely like the present Going Merry and built to the Merry's specifications, it actually wouldn't end up being precisely the same, because of inevitable variations in the construction material. It wouldn't be the same ship and the crew would definitely feel that it wasn't the same ship, even if it was built the exact same way, making it pointless to build the same ship from scratch rather than just building or buying a new one.
  • In the Alternate History of Code Geass, the British Empire kept and expanded upon their colonies in the Americas, then lost the British Isles themselves to Napoleon's invasion. Since the royal family that escaped to the American colonies couldn't accurately call themselves "British" anymore, and apparently didn't consider themselves "Americans" either, they called their territories from then on "the Holy Britannian Empire".
  • In Land of the Lustrous, the Lustrous are people made of gems, so if parts of their body are broken off, they can receive new material to replace those parts. Phosphophyllite, however, is an exception, because they is a rare type of gem, so it is very important that they avoid fracturing as much as possible due to their extreme fragility. On the other hand, Phos' body is compatible with using the body parts of other gems. Over the course of the series, Phos has lost their legs and had them replaced by agates, had their arms replaced by a gold & platinum alloy, body replaced by crystals, their head replaced by the head of a whole gem, Lapis Lazuli, and left eye replaced by a pearl. Rutile discusses this trope by the time they replace Phos's head, since half of Phos's body is by that point from other gems, wondering if they can even be called "Phosphophyllite" anymore.
  • In Battle Angel Alita characters such as Alita frequently replace their entire bodies with robot ones, with their still-organic brains being the only still-human part of them. Alita eventually finds out that after getting blown up by Desty Nova and reconstructed in-between the original manga and Last Order, her brain was replaced with a Tipharian brain chip with her memories uploaded into it, leaving absolutely nothing left of her original physical being, and the resulting identity crisis causes her to literally disintegrate. Don't worry, she gets better.
    • The revelation that Tipharians' brains are replaced with brain chips without their knowledge, meaning that while they still have their original bodies they are effectively copies of their original selves is a huge shock to these characters, one of which actually saws his head open with a circular saw to check and then Goes Mad From The Revelation shortly before jumping to his death.
  • A recurring theme in the Ghost in the Shell franchise, where characters can replace every single bit of their organic body with mechanical prostheses, including uploading themselves to a cyberbrain. The term "Ghost" is used to refer to an intangible essence (akin to a soul) that makes such full-body cyborgs human instead of just highly-advanced robots with human memories.

  • In the Stanley Holloway monologue The Beefeater when visiting the Tower of London they are told that the axe on display "has 'ad a new handle, and perhaps a new 'ead, but it's the old, original axe".

    Comic Books 
  • The Ultimates (2015): During a chat between the newly redefined Galactus and the Molecule Man, the latter brings up the recent destruction and rebirth of the multiverse. Owen asks whether, given that so many and so much transitioned through, whether the old omniverse ever died at all, and what that means (especially in regards to Galactus' role in all of it.)
    That omniverse died. But a lot of the lives in it carried on to the new one. Same broom—new handle. So. Did the omniverse die? Are we the eighth cosmos, or still the seventh?
  • In a 2017 issue of The Avengers, the Vision has a conversation with a future version of himself who apparently lasted until the end of time. When present-Vision is disturbed at the notion that he'll outlive all his friends, future-Vision cites Theseus' Paradox to question if they're technically the same person.
    Vision: I grant your query, but regardless of how many of my—your—artificial limbs and organs may have been exchanged, your intangibles—your brain patterns—will forever remain based on an ex-Avenger named Simon Williams.
    Future-Vision: ...
    Vision: Won't they?
  • In The Manhattan Projects, as his injures start piling up, Von Braun has replace more and more of his body with primitive cybernetics. He begins to privately wonder how long it will be before he’s all machine, and if he’ll still qualify as the same person afterwards.
  • Guardians of the Galaxy (2020): Discussed between Drax and his daughter Moondragon in issue 3, regarding Drax, who thanks to various shenanigans, deaths, resurrections and messes with the Soul Stone is unsure whether he's really the same Drax or Arthur Douglas, and is unsure whether he owes anything to them.

    Fan Works 
  • Eugenesis: Towards the end, Nightbeat dies, but leaves behind a device and blueprint that will allow the others to rebuild him. Afterwards, he reflects on this trope; he’s exactly like he was down to the very second that he died, but he’s been built from the ground up and doesn’t have one bit of his original body in him. So does that make him a clone rather the original Nightbeat?
  • In Forged Destiny, Jaune creates Crocea Mors to the exact same specifications each time he crafts it. The original steel sword was shattered in the battle with Watts but Jaune gathered some of the shards and reforged the blade using Vacuan Silver. Jaune perfectly recreates the blade again when he gets hold of some enchanted metal. When that blade is similarly broken, he makes a new sword from scratch but still with the same shape, weight, balance, and reach as each of the previous ones. Each of these swords is still Crocea Mors according to Jaune's second Passive, Blade Bond, which increases damage dealt in proportion to the length of time the same sword has been wielded.
  • In the My Little Pony: Friendship Is Magic fan fic The Cutie Mark Crusaders Bring About The Apocalypse, a revived Discord switches the Mane 6's bodies around, and then causes their memories and personalities to be slowly replaced by those of the pony whose body they now inhabit. Discord then further messes with them by explaining this trope to them, causing them to wonder if the original Mane 6 will still truly exist once they completely switch.

    Film (Animated) 
  • Waking Life has one segment with two women taking about being in their fifties, and that how people have to make up stories about who they were when they were younger. As noted in the Real Life segment, the human body is constantly regenerating cells, so they're both completely new people several times over since they were infants.
  • In WALL•E, it's implied that the titular robot had at one point or another replaced every part of his body from one of the robot spares he keeps in his house, except his motherboard. So, by the end, when Eve replaces his motherboard after it gets severely damaged, Wall-E acts like any other garbage disposal robot until Eve kisses him.

    Film — Live-Action 
  • The Beast in The World's End. It's had every meaningful part replaced, but looks the same and runs about as junkily as it did in the '90s. This foreshadows what the Network has done to Newton Haven: it claimed the place was "better" and only killed and replaced who it needed to, but over the last two decades only three of its human residents remained and most of the local culture has been erased. All this leads to Gary, Andy, and Steven asking the Network how it can consider it the same town.
  • John Dies at the End: The film opens with David beheading a body with an axe. However, the handle breaks and he gets the handle replaced. Later, he chips the head killing a centipede... thing. Eventually, the guy he beheaded comes Back from the Dead, and the reanimated corpse points to the axe and says, "That's the axe that slayed me," to which David asks the audience, "Is he right?" The plot point from the original book that this question foreshadows was removed from the film.
  • In A Christmas Story, Ralph notes that the Old Man's tires were only tires in the academic sense. "They were round, and at one point were made of rubber."

  • Questioned in The Last King. The narrator wonders whether, after replacing each and every part of his grandfather's axe, it is still the same axe.
  • Oz stories
    • An early example is the Tin Woodman from The Wonderful Wizard of Oz. He pissed off a witch who enchanted his ax so that it would cut off pieces of him, and he went to a tinsmith to replace the missing parts. Eventually he was made entirely out of tin - but since it was a gradual process, he's still human Nick Chopper and not a new person. Even more paradoxically, however, and with more than a bit of Fridge Horror, the tinsmith kept the old head in a closet, where, due to the no-death nature of Oz, it remained sentient, desiring nothing to do with the Tin Man when he returned to retrieve it. His beloved eventually went on to marry a person assembled out of all the cut-off pieces.
    • In The Road to Oz, Jack Pumpkinhead is shown with a garden of new pumpkins grown to replace his head whenever the current pumpkin spoils. He claims that since the head is the smaller part of his body, he remains the same person. Also, in The Marvelous Land of Oz, one of his legs is used to replace the broken leg of Sawhorse, and is later replaced in turn by a table leg. Neither seems affected by the change.
  • The Fifth Elephant
    • Brought up several times, generally in regards to a Dwarfish axe which has been passed down through the family for generations: sometimes the head needed replacing, other times the shaft, still more times the eye or the bit, but it's still the same ancestral axe, and it works all the better for having changed when it needed to.
    • Played to the hilt in the book's climax, where no one's terribly upset that the conspiracy to influence the Dwarfish succession involved destroying the Scone of Stone and replacing it with a perfect replica: the Scone had already been replaced many times over the centuries, but it had always remained "the thing and the whole of the thing."
    • Another Discworld novel discusses the example of a witch's broom that is malfunctioning. No matter what part of the broom got replaced—and eventually, all parts of the broom have been replaced at least once—the malfunction stubbornly refused to disappear.
    • In The Shepherd's Crown, dwarfish craftsmen finally get the chance to do a proper repair job on Granny Weatherwax's broom. This essentially involves building an entirely new stick around the idea of Granny Weatherwax's broom. It gets compared to the axe above in a footnote.
  • The Belgariad. Alluded to in the Malloreon series. Poledra tells Beldin that she's surprised he hasn't changed his tunic during the thousands of years since she last saw him. Beldin says that he patches it, and replaces the patches as they wear out, to the point that the original tunic "is only a memory".
  • Brandon Sanderson's book Alcatraz vs. The Scrivener's Bones discusses this trope.
    Alcatraz: I used to be a young, idealistic hero. But like the ship of Theseus, that person has been changed so many times it no longer exists. If it ever did in the first place.
  • Brandon Sanderson's Cosmere touches on this, but not in as many words. All things—including objects—have a physical, cognitive, and spiritual element. The cognitive element involves how the object is viewed, and how it views itself. A ship is just a few awkward pieces of wood, except people think of it as a ship, so eventually it begins thinking of itself as a ship as well. This provides a solution to the paradox: As long as the repairs and replacements are done slowly enough that people still think of the ship as the same ship, the ship itself will agree.
  • Honor Harrington mentions that a particular chair has been in the Protector's Palace nursery for over seven hundred years, plus or minus the odd frame repair or reupholstering.
  • John Dies at the End: The book begins with exploring this question. David beheads a body, but the handle breaks on the last swing. He replaces it. He later chips the head on another supernatural creature, and replaces it. When the guy he beheaded comes Back from the Dead, the reanimated corpse points to the axe and says, "That's the same axe that beheaded me," to which David asks the reader "is he right?" This question foreshadows the question of whether "monster Dave" can be considered the same person as the original human Dave that he unwittingly replaced.
  • In the BattleTech novel Close Quarters this is referred to with an old Jenner 'Mech which is "one of the first" ever made—except that every single part, down to even the last nut and bolt, has been replaced over the last 600 years two or three times or more!
  • Plutarch's Parallel Lives is the Trope Maker and Trope Codifier. He describes the trope and concept in a famous paragraph in his Life of Theseus:
    The ship wherein Theseus and the youth of Athens returned 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.
  • Played with in the Shannara books, when Morgan Leah says that every part of the ancestral sword of the Kings of Leah has been replaced multiple times—except for the actual blade, which is over three hundred years old and is still in perfect condition. This is what makes him believe that the story of Alannon enchanting the sword three hundred years previous is true (Which it is).
  • Touched on towards the end of Siddhartha by Hermann Hesse. One of the keys to the titular character's (eventual) enlightenment is coming to understand that "you cannot step into the same river twice" (because the water which makes it up has kept flowing downstream)
  • In Scott Lynch's short story “A Year and a Day in Old Theradane,” a group of thieves is tasked with stealing a city street that is a Place of Power. Their solution falls on one side of this trope: Over the course of a few days, they steal and replace all of the cobblestones. When they're done, the street is still there, but all of the parts that made it up originally are gone, which destroys the location's magical power.
  • In Armageddon III: The Remake by Robert Rankin, the 25th century Private Detective Lazlo Woodbine describes his standard issue fedora thusly:
    Same hat my ancient ancestor wore back when he was a private eye in the nineteen-fifties. Sure it's had thirty new brims, eighty new bands and more crowns than the House of Hapsburg since then, but it's the same hat. Same old hat, same old joke. Class never dates, see?
  • Hinted at in the Star Wars Legacy of the Force series. While flying Slave I in his introduction, Boba Fett muses that the only part of the ship that remains from his father's days of piloting it was the pilot's chair.
  • Invoked with Marvin the Paranoid Android in So Long, and Thanks for All the Fish. Over the course of four books, the hapless robot has been thrown back and forth through time then left to fend for himself so frequently he is now 37 times older than the universe, and almostnote  every part of him has been replaced at least 50 times.
  • Fletcher of Card Force Infection has used "the same" deck since he first got into Card Force shortly after his parents divorced, though numerous little changes over the years mean that it doesn't actually have any of the same cards it had then. Losing it to Maxwell is directly compared to "sinking the Ship of Theseus".
  • Tomorrow the World by John Biggins. Because the Austro-Hungarian navy is starved of funds thanks to weak commanders and political wrangling, they use 'official reconstruction' to build a new ship under the guise of repairing an old one. The sailing ship the protagonist is on has been broken up and rebuilt twice, yet keeps the same name to maintain the subterfuge. Naturally this trope is lampshaded.

    Live-Action TV 
  • A popular example comes from the British sit-com Only Fools and Horses, where Trigger, one of the characters, is given a medal for owning the same broom for 20 years, although it has had 17 new heads and 14 new handles. When asked how can it be the same broom, Trigger holds up a picture of himself and his broom and says, "Well, here's a picture of it, what more proof do you need?" As a result, the paradox is sometimes known in the UK as "Trigger's Broom."
  • The same joke appears in David Jason's previous sitcom Open All Hours:
    Granville: We need a new brush.
    Arkwright: Nonsense! That's a marvelous old brush, that! I've had that for fourteen years. It's only had two new heads and three new handles.
  • Discussed in an episode of Star Trek: Deep Space Nine. Kira's Romantic False Lead Bareil Antos gets injured and has part of his brain replaced with cybernetics. As more of his brain fails and is replaced, the less he's him. Eventually he's mostly cybernetics, and rather than continue the process Kira allows him to die.
  • Discussed and played straight in the Doctor Who episode "Deep Breath". The antagonist of the episode is harvesting human organs to be able to pilot the ship, but in doing so, he has replaced most of the ship, and of himself. Capaldi's Doctor lampshades this by saying "If you have a broom, you replace the handle, and then you replace the brush, and do it over and over, is it still the same broom? The answer The subtext of the conversation concerns the Doctor themself, who periodically regenerates, taking on a new appearance and personality. It's been said that the process replaces every cell in their body, yet they remain fundamentally the same person. During the episode in question, the Twelfth Doctor was newly regenerated and uncertain of his true identity.
  • Played for laughs in Cheers when a con artist tries to sell "George Washington's Axe," but then has to explain that all the parts have been replaced over the centuries.
  • Dolores on Westworld has been repaired so many times over the years that she's practically brand new, with at least one character noting that she's one of the "older" robots in the park purely on a technicality. It remains to be seen how much, if anything, remains of her original components or programming.
  • Star Trek from the beginning has begged this question ever since it was described how the transporters work. The transporter's function on the show was to be a magic elevator that took the away team to the planet without requiring the director to film a shuttle landing over and over again. The transporters work by dissolving the away team member and assembling a copy of them on the planet below, which makes you wonder if the same consciousness is moved also. Further questions are begged when you consider that in an episode of Star Trek: The Next Generation, a glitch in the transporter created a copy of William Riker who was marooned on the space station he was transported from, with tests affirming that both Rikers should be considered to be the 'real' one as nobody could determine a difference beyond the fact that one had been trapped on another planet for eight years. Yet more questions are begged when one episode features the only POV shot in the entire series of someone going through the transporter and mid stream being bitten by the Monster of the Week which suggests that the experience of being transported has no break in consciousness. There have also been two instances of conversations continuing between beaming subjects mid-beam in the TOS movies; Kirk explaining the "By The Book" subterfuge to Savvik in Star Trek II, and the badly timed rescue beam-out from Rura Penthe in Star Trek VI.
  • Invoked but defied in Power Rangers Operation Overdrive after the android Red Ranger Mack is 'killed' in the final battle; Mack's overall body still appears intact, so there should be nothing to stop Hartford (his creator/father) using his body and reactivating a new consciousness, but Hartford makes it clear that anything he recreated that way wouldn't be Mack, but just "something that looked like him".
  • Robot Wars
    • During an interview about Matilda on the "House Robots" special DVD, it was mentioned that she'd been upgraded so extensively over the course of the first five series that barely any of her original parts were being used at all. When the presenter joked that the only remaining original part was the strap holding the back of her shell on, her supervisor admitted that even that wasn't there originally; it had been added for Series 4 to stop the shell falling off every time she was flipped.
    • When the series was rebooted in 2016, all-new and massively updated versions of Sir Killalot, Shunt, Dead Metal and Matilda were created to face the new generation of competitors. Despite being completely new machines incorporating no components of the long-retired originals, nobody ever questioned that they were the same House Robots "returning" to fight again.

    Visual Novels 
  • One of the many digressions that comes up during Nine Hours, Nine Persons, Nine Doors involves the Ship of Theseus.
  • Lucy and the protagonist end up having a discussion on this in Lucy ~The Eternity She Wished For~, since over time Lucy could end up having her entire body replaced part by part, and even her memories can be deleted or modified. By the end of the game, Lucy is destroyed completely (even her memory chips are fried and unsalvageable,) and the protagonist spends the next 15 years learning robotics to try and recreate her from scratch with her memories intact. At first, it seems like he only succeeded in creating a mere copy of the original Lucy, until he's finally able to trigger her memories to come back.

    Video Games 
  • In NieR: Automata, the merchant in the Resistance camp has a damaged leg which he is reluctant to replace as it is the last remaining piece of his original body, and he ponders whether he would still be himself without it.
  • Mega Man Zero 3 reveals at the end of the game that Omega's true form is Zero's original body, Zero having been uploaded into a copy body prior to the events of the Zero series. Defeating Omega means destroying his own original body. Fortunately, X appears to reassure Zero that he's still Zero despite his copy body, and Zero carries through with destroying Omega.
  • In Video Game/SOMA the main character, Simon, is revealed to be a robot with the memories of the original Simon, who had his brain scanned and then died almost a century before the events of the game the topic is brought up several times, most notably when Simon changes into a new diving suit(read: body), only to discover that the process actually involved making a copy of his mind and uploading it, leaving the original body alive. The player is left with the choice of abandoning it or ending its suffering.
  • In Yandere Simulator, Ayano can speak online with Selene2005, who brings up this paradox as an alternative discussion topic instead of their… preferred topic of discussion.
  • In the RPG Megatraveller: The Zhodani Conspiracy (based on the Traveller game), if any of your party members dies you can recruit a replacement at the spaceport, who will carry on in their stead just as good as anyone else. But if all of the original members are dead, the game ends even if everyone else is alive. The recruits just don't have the same commitment to the original quest.
  • In Fallout4 and Fallout76 some weapons have bonus effects, which are preserved even if you replace every component of the weapon with a different one, even going so far as to turn a wooden bat metal.

    Web Comics 
  • The first warship seen owned by the Tagon's Toughs in Schlock Mercenary was the Dragon-class cruiser Kitsefear. After her destruction early on in the comics, she was eulogized in a footnote that mentioned that "her hull had been patched so many times it's hard to say where the original hull sits."
  • Girl Genius: Tarvek would be the first to admit that Anevka has been... different since being given a puppet clank body after her "accident." Though the real problem is that as Anevka slowly sickened inside her life support chamber, her clank body took up more and more of the slack until even the clank failed to notice that Anevka had died — and the clank was becoming increasingly erratic. Tarvek shut her down for safety's sake as much as anything else.
  • Saturday Morning Breakfast Cereal parodies this here by having an alien claim that humans only live about sixteen hours. Sure the body persists for decades, but if life is continuity of consciousness and humans spend eight hours a day unconscious than over those decades 30,000 people or so will inhabit it. The votey reveals he's just messing with her.

    Web Original 
  • Matt Santoro discusses this paradox in his video The 10 Most MIND-TWISTING Paradoxes of All Time!.
  • This trope is alluded to by CinemaSins in their sins video for Cars:
    "Also, if every part of these cars are actual living appendages and need to be changed periodically, like the tires — it really starts to make you ponder the question, 'If I replace all the parts of an old car, is it the same old car or is it a new car?'"
  • Discussed Trope in Stray Ami - Blank and Andale decide it's different with people.
  • Something of a theme in gen:LOCK when it comes to the titular gen:LOCK technology. One can even see the phrase "Ship of Theseus" pinned to a wall in Dr. Weller's lab. As it turns out, when the gen:LOCK program first got started, the doctor made a habit of uploading Chase's mind into two cyberbrains simultaneously, one running a Holon, and the other a spare copy. After the Union captured Chase (eventually turning him into the Nemesis), Dr. Weller uploaded the copy back into Chase's body and kept it a secret. So the question becomes: which mind is the real Chase? Both? Neither?

    Western Animation 
  • In the Bump in the Night episode "Farewell, 2 Arms", Molly gradually replaces bits of her body with tougher parts in order to become stronger. As she does so, she gradually becomes more and more cruel and domineering. This culminates in her ripping off her own head, the last part of her original body, and replacing it with a staple remover. Squishington manages to reattach the head to her original body, which resets Molly to her original, gentle personality. She then confronts the form she made over the course of the episode, which is still rampaging, and claims to be what Molly always wanted to be. Molly admits she was wrong.
  • Joked about in an episode of Family Guy. Joan Rivers was doing interviews on the red carpet of the Adult Video Awards, and said that she was once asked to do a porno but couldn't because, since she's had so much plastic surgery, more than 50% of her body was under 18 years of age.
  • Invoked in the Futurama episode "The Six Million Dollar Mon", in which Hermes continually "upgrades" himself by replacing various organic parts with robotic prostheses. As each human part is removed, Zoidberg salvages it and stitches them back together. After the final organic piece of old!Hermes, the brain, is replaced and reattached to new!Hermes, there are two Hermeses: an organic one with all the parts of the original (plus a whole lot of stitches), and a robotic one controlled by the processor of the psychopathic robot Roberto.

    Real Life 
  • American philosopher Theodore Sider proposed a solution to this paradox by considering objects from a four-dimensional perspective rather than a three-dimensional one. If objects are thought of as a four-dimensional "river" of three-dimensional "time slices," then each "slice" could still be part of the "river" while remaining unique from one another. In this way, an object can still be considered itself even when all of its components are eventually replaced. Another way to put it is that the essential "identity" of something can "fix itself" over time, as long as the process is gradual. One practical way to look at it is product brand refreshes. The whole "new look, same great whatever" depends on consumers recognizing the refreshed packaging as the same product, getting used to it over time, and then the process repeats again down the line.
  • It's commonly held that the human body replaces all of its cells (in some versions, all of its atoms) at regular intervals, usually given as either seven or ten years. While cells do continually die off and are replaced with new ones, they do so at different rates, with no regular cycle of years. There are also exceptions, such as neurons in the brain and parts of the skeletal structure, which last a lifetime and are not replenished. Therefore, after a few decades, a person will be composed of almost entirely different physical matter.
  • A number of wooden vessels built during the Age of Sail exist to this day, but over the course of their lifespan they have had numerous refits in which timbers in disrepair or rot were replaced with new material:
    • The first rate ship-of-the-line HMS Victory, the oldest actively commissioned warship. In a 2009 interview, one of her commanding officers LCDR John Scivier estimated that 10 to 15 percent of her hull remains original.
    • The frigate USS Constitution, "Old Ironsides," is the oldest active commissioned warship still afloat and sailing. The Naval History and Heritage Command's Boston detachment has also estimated that 10 to 15 percent of her hull is still original.
    • Unlike Constitution and Victory—which most agree are not replicas—the War of 1812-vintage brig Niagra is more commonly considered a replica rather than the restored original. Her third reconstruction in 1986 found that most of the wood comprising her hull was badly decayed, and so the ship was almost completely rebuilt save for various non-structural timbers which were salvaged and reused.
    • USS Constellation is even more complicated and a little controversial. According to the US Navy's records, the 1797 frigate USS Constellation was given a major refit in 1854 turning her into a sloop of war. However, some contemporary accounts and analysis of the current ship indicates that USS Constellation was broken and up and sloop of war built from her timbers plus some in Navy stockpile. This was done as a scheme to secure funding from a congress that might have been wary of funding construction of an entirely new vessel. It's now more common to list the frigate and surviving sloop as different vessels.
  • There have been cases of multiple different automobiles each having a claim to being the "original" vehicle driven by a famous celebrity or racer, as a result of the vehicle having been broken down for parts at some point, leading to there being, for instance, one vehicle based upon the original chassis, another with the original bodywork, and a third with the original engine.
  • Buddhism considers every aspect of reality to be affected by this, but with a special focus on humans and our personalities, since we constantly change at a slow but steady rate. So are you the same person you were ten years ago? Interestingly the solution offered is that you aren't, and that your 'self' as you usually see it is an illusion. On a broader note, since everything is constantly changing nothing can really be said to exist or be stable, and trying to deny this or ignore it causes suffering.
  • Pop groups can get like this - the Sugababes have replaced all three original members while keeping the same name (the three originals subsequently reformed as a new band and attempted to sue to get the name back, unsuccessfully), while there's at least six different iterations of the Four Tops floating around.
  • One way to look at this problem from a computer science perspective is to look at the difference between call-by-value and call-by-reference. Call-by-value passes in data from a location in the computer's memory, usually by copying it to a new location temporarily. Call-by-reference passes in the location itself, which will probably work the same way unless the data in that location changes later on. So how do you tell if two variables are "the same?" Depends whether the data or the location is important, and there are cases for both. Some languages, like Javascript, even have separate "equality" (==) and "identity" (===) operators just for this purpose.
  • Happened to Douglas Adams when he visited Kinkaku-ji in Japan (which he wrote about in his non-fiction book Last Chance to See), and found that it looked suspiciously new. He asked about it and was told that the building burned down, and was rebuilt from all-new materials. And that this had happened multiple times. He asked how it's the same building then, and was told "It's always the same building". Adams concluded that someone was missing the point, but that it might have been him.
    "The intention of the original builders is what survived. The wood of which the design is constructed decays and is replaced when necessary. To be overly concerned with the original materials, which are merely sentimental souvenirs of the past, is to fail to see the living building itself."
  • The members of the Progressive Rock band Yes have come and gone so often that the band has been compared to a musical version of the Ship of Theseus. The current lineup features none of the founding members.
  • Wiki articles. Because they're communally edited, over time they may get to a point where very little of the original wording will have been written by the original writers of the article, even if only small bits are edited at a time rather than the page undergoing a complete overhaul.
  • Sports teams. Can the identity of the team really maintain continuity even as players and managers come and go? Are the Chicago Cubs who won the World Series in 1908 and the Chicago Cubs who won the World Series in 2016 the same team in any meaningful sense?
  • The book Pink Floyd and Philosophy discussed this in a chapter devoted to Pink Floyd's lineup. The conclusion was that Pink Floyd could be said to be Pink Floyd as long as either David Gilmour, Richard Wright, or Nick Mason were present. The chapter's title: "The Dinner Band on the Cruise Ship of Theseus."
  • Stephen Fry once wrote an article in which he describes the phenomenon as "P.G. Wodehouse's Typewriter", and claims that, since every cell in the human body dies and is replaced at some point in your life, the embarrassing photos of him playing naked in the garden as a child (that his mum used to love showing to his friends when they came to visit) are technically not photos of him.
  • Valve's Source Game Engine was developed from the "GoldSrc" engine used for Half-Life 1, which itself was a heavily modified version of the original Quake I engine. Per John Carmack, there are still bits of early Quake code in Half-Life 2. Valve have had no legal issues licensing Source to other developers, suggesting that it's different enough to not be an issue.

Alternative Title(s): Ship Of Theseus


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