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 prosthetics. 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?
- 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.
- 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.
Live Action TV
- Questioned in The Last King. The narrator wonders if, after replacing each and every part of his grandfather's axe, it is still the same axe.
- 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.
- 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.
- 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."
- 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. Paraphrased a little:
- 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.
- 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 produces a picture of himself and his broom and asks, "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.
- The USS Constitution, sometimes known as 'Old Ironsides' and the oldest commissioned warship still afloat. It has been around so long and had so many parts replaced that it's open to discussion if a single one is original.