Theseus' Ship Paradox

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?

Say you have an object that is sufficiently important, even if only for its sentimental value, that simply throwing it away when it wears out isn't an option. Instead, it gets replaced in piecemeal fashion: old and rotting timbers get replaced, rips and tears get patched, missing limbs and organs get prostheses. As this process repeats, the thing in question is made up less and less of its original parts and more and more of replacements to the point that, one day, you simply aren't going to have anything of the original left. The question is, once this happens, is it still the original object or not?

More properly known as the "Ship of Theseus" or "Grandfather's Axe" paradox, this trope presents a classic philosophical conundrum. While it's often played for comedy, as common wisdom would suggest that, no, it's not still the same axe once its head and handle have both been replaced (though its owner will stubbornly insist to the contrary), sometimes it has more dramatic implications: if a person has his brain gradually replaced with electronics, for example, at what point do we cease to have a human with bits of machine in their brain and start to have a machine with bits of human in its brain? Do we ever? This scenario can also get thorny if someone rebuilds the thing in question from the discarded parts: if you have both a "new" thing made from the original material and an "original" thing made from new material, which one, if either, is the "real" one?


    open/close all folders 

  • 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 though, 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 a new ship from scratch rather than just buying a new one.

    Comic Books 
  • The Ultimates (2015): During a chat between the newly redefined Galactus and the Molecule Man, the later brings up the recent destruction and rebirth of the multiverse. Owen asks whether, given 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?

    Film (Animated) 
  • 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?"

  • 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: Like the film, 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?"
    • Unlike the film, this question becomes a much more relevant and existentially terrifying philosophical conundrum toward the end of the book when we learn narrator!David killed and replaced original!David sometime earlier.
  • 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!
  • 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.

    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?"
  • 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 is no, but you can still sweep the floor, and that's actually irrelevant."
    • Ironically, that wasn't actually irrelevant on either a practical or metaphorical level. It just detracted from his point while he tried to employ Talking the Monster to Death.
    • The subtext of the conversation concerns the Doctor himself, who periodically regenerates, taking on a new appearance and personality. It's been said that the process replaces every cell in his body, yet he remains fundamentally the same man. 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. 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.

    Visual Novels 

    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."

     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?'"

    Western Animation 
  • In one episode of Bump in the Night, 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.
  • 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.
  • 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.

    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.
  • 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 visits Kinkaku-ji in Japan (which he wrote about in his non-fiction book Last Chance to See), and finds that it looks suspiciously new. He asks about it and is told that the building burned down, and was rebuilt from all new materials. And that this has happened multiple times. He asks how it's the same building then, and is told "It's always the same building". Adams concludes that someone is missing the point, but that it might be him.
  • 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.

Alternative Title(s): Ship Of Theseus