Ship of Theseus

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In the metaphysics of identity, the ship of Theseus is a thought experiment that raises the question of whether an object that has had all of its components replaced remains fundamentally the same object. The concept is one of the oldest in Western philosophy, having been discussed by the likes of Heraclitus and Plato by c. 500–400 BC.


The thought puzzle was discussed by ancient philosophers such as Heraclitus (Cratylus 401d) and Plato (Parmenides 139),[1] later by Plutarch,[2] and more recently by Thomas Hobbes and John Locke. Several variants are known, including the grandfather's axe, which has had both head and handle replaced. This is itself an example of Ship of Theseus, as the original story has had various elements replaced over time.

The particular "ship of Theseus" version of the thought puzzle was first introduced in Greek legend as reported by the historian, biographer, and essayist 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 places, 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, Theseus[2]

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 then used to build a second ship.[3] Hobbes asked which ship, if either, would be the original ship of Theseus.

An ancient Sanskrit Buddhist text titled Mahāprajñāpāramitopadeśa, which was later translated into Classical Chinese (Da zhidu lun 大智度論), contains a similar philosophical puzzle.[4]

Thought experiment[edit]

It is supposed that the famous ship sailed by the hero Theseus in a great battle was kept in a harbor as a museum piece, and as the years went by some of the wooden parts began to rot and were replaced by new ones; then, after a century or so, every part had been replaced. The question then is whether the "restored" ship is still the same object as the original.

If it is, then suppose the removed pieces were stored in a warehouse, and after the century, technology was developed that cured their rot and enabled them to be reassembled into a ship. Is this "reconstructed" ship the original ship? If it is, then what about the restored ship in the harbor still being the original ship as well?[5]

Proposed resolutions[edit]

No identity over time[edit]

This solution was first introduced by the Greek philosopher Heraclitus who attempted to solve the thought puzzle by introducing the idea of a river where water replenishes itself as it flows past. Arius Didymus quoted him as saying "upon those who step into the same rivers, different and again different waters flow".[6] Plutarch disputed Heraclitus' claim about stepping twice into the same river, citing that it cannot be done because "it scatters and again comes together, and approaches and recedes".[7]


Ted Sider and others have proposed that considering objects to extend across time as four-dimensional causal series of three-dimensional "time-slices" could solve the ship of Theseus problem because, in taking such an approach, all four-dimensional objects remain numerically identical to themselves while allowing individual time-slices to differ from each other. The aforementioned river, therefore, comprises different three-dimensional time-slices of itself while remaining numerically identical to itself across time; one can never step into the same river-time-slice twice, but one can step into the same (four-dimensional) river twice.[8]

Cognitive science[edit]

According to Noam Chomsky, as described in Of Minds and Language (2009), the thought puzzle arises because of extreme externalism: the assumption that what is true in our minds is true in the world.[9] This is not an unassailable assumption, from the perspective of the natural sciences, because human intuition is often mistaken.[10] Cognitive science would treat this thought puzzle as the subject of an investigation of the human mind. Studying this human confusion can reveal much about the brain's operation, but little about the nature of the human-independent external world.[11]

Following on from this observation, a significant strand in Cognitive Science would consider The Ship not as a thing, nor even a collection of objectively existing thing-parts, but rather as an organisational structure that has perceptual continuity.[12] When Theseus thinks of his ship, he has expectations about what can be found where, how they interact, and how they interact with the wider world. As long as there is a time/space continuity between this set of relationships, it is The Ship of Theseus. An organisational structure of course has to have components, but these also are defined in the same way. Such a recursive structure must "bottom out" somewhere and the enactivists[13] see this grounding to be based in our embodied relationship with our environment. In Cohen's (see below) example where a scavenger follows Theseus, collecting the discarded parts of the original Ship of Theseus and then re assembles them, the reassembled ship is not The Ship of Theseus because, presumably a court of law would say, Theseus does not have the "owns" relationship with the reconstructed ship.

Gradual loss of identity[edit]

As the parts of the ship are replaced, the identity of the ship gradually changes, as the name "Theseus' Ship" is a truthful description only when the historical memory of Theseus' use of the ship—his physical contact with, and control of, its matter—is accurate. For example, the museum curator, before any restoration, may say with perfect truthfulness that the bed in the captain's cabin is the same bed in which Theseus once slept; but once the bed has been replaced, this is no longer true, and the claim would then be an imposture, because a different description would be more accurate, i.e.; "a replica of Theseus's bed". The new bed would be as foreign to Theseus as a completely new ship. This is true of every other piece of the original ship. As the parts are replaced, the new ship becomes exactly that: a new ship. Hobbes' proposed restored ship built from the original parts will be the original ship, as its parts are the actual pieces of matter that participated in Theseus's journeys. A real world example of this would be the USS Constitution, where multiple refittings and restorations over its 200 years of service have removed most of the original parts.[14]


The thought puzzle appears in several more applied fields of philosophy.

In philosophy of mind, the ship is replaced by a person whose identity over time is called into question.[citation needed]

In both philosophy of law and practical law, the thought puzzle appears when the ownership of an object or of the rights to its name are disagreed in court.[citation needed] For example, groups of people such as companies, sports teams, and musical bands may all change their parts and see their old members re-form into rivals, leading to legal actions between the old and new entities. Also, texts and computer programs may be edited gradually but so heavily that none of the original remains, posing the legal question of whether the owners of the original have any claim on the result.

Yes, Blackfoot, Blood, Sweat and Tears, Thin Lizzy and Ratt are examples of rock bands that have retained their names despite member reshufflings to the degree that none of the founding members of the respective bands remain.

In ontological engineering such as the design of practical databases and AI systems, the thought puzzle appears regularly when data objects change over time.[citation needed]

A literal example of a Ship of Theseus is DSV Alvin, a submersible that has retained its identity despite all of its components being replaced at least once.[15]

RNA, a central polymer of life, has been proposed to have evolved from an earlier genetic polymer in a manner that makes it a biological example of a Ship of Theseus.[16]

In architecture, Lance Hosey has proposed that the Barcelona Pavilion is "modern architecture's ship of Theseus." Demolished and rebuilt in exacting detail on the original site, can it be considered the "same" building? He thoroughly documents the ambivalence of architects and historians about this question.[17]


There are many explicit or implicit references to the Ship of Theseus in books, television, film, music, software, and games.

In 2012, the Indian film Ship of Theseus explores "questions of identity, justice, beauty, meaning and death through the stories of an experimental photographer, an ailing monk and an enterprising stockbroker," each of whom has received an organ from a deceased person.

The 2020 album Low Key, by Australian artist Jackmann, features the track “The Ship of Theseus”. The song details the demise of a relationship as its two parties grow apart due to personal changes brought on from life experiences. Jackmann explores the idea that over time, though on the outside, people may not change much, life can completely transform who we are to the point we become totally different in the eyes of someone who once loved us, and that who we once were no longer exists. “The planks that held us together were one-by-one replaced, and the things that made us who we were, were one-by-one erased. Long before we parted, had it all changed?”

In the 2021 Disney+ series WandaVision, the ship of Theseus is brought up at a critical point in the climactic battle between Wanda's Vision and White Vision. Originally, the android Vision was killed by Thanos in Avengers: Infinity War. A few weeks after the events of Avengers: Endgame, Wanda created a new version of him, with his original personality and emotions, but no true body outside of the Hex in Westview, New Jersey. Meanwhile, S.W.O.R.D. repaired Vision's original body, but this version lacked emotions, memories, personality, and color. S.W.O.R.D. sends in this new White Vision to assassinate Wanda and her created Vision. As the fight between the androids takes them into the local library, Wanda's Vision directly references the thought experiment and recites it in an attempt to resolve the conflict diplomatically and philosophically. The two Visions explore the paradox of their shared identity, coming to an understanding that neither of them can be the true Vision, yet both must be the true Vision. Wanda's Vision overrides White Vision's S.W.O.R.D. protocols and restores his memories to him, and White Vision flees the battle, presumably to reevaluate everything that had happened to him up until this point in the franchise.

In 2021, the myth is also explored in season 4, episode 6 of The CW TV series, Black Lightning ("The Book of Ruin: Theseus's Ship") as the appearance of Jennifer Pierce (Lighting) changes after she is "reconstructed" after exploding into energy in the ionsphere.

See also[edit]


  1. ^ Plato (1925). Parmenides. 9. Translated by N. Fowler, Harold. London: Harvard University Press. p. 139.
  2. ^ a b Plutarch. "Theseus (23.1)". The Internet Classics Archive. Retrieved 2008-07-15.
  3. ^ De Corpore, ch 11.7
  4. ^ Huang, Jing; Ganeri, Jonardon (2021). "Is this me? A story about personal identity from the Mahāprajñāpāramitopadeśa / Dà zhìdù lùn". British Journal for the History of Philosophy. doi:10.1080/09608788.2021.1881881. An ungated version is available here
  5. ^ Cohen, S. Marc (2004). "Identity, Persistence, and the Ship of Theseus". Retrieved 2019-03-15.
  6. ^ Didymus, Fr 39.2, Dox. gr. 471.4
  7. ^ Plutarch. "On the 'E' at Delphi". Retrieved 2008-07-15.
  8. ^ David Lewis, "Survival and Identity" in Amelie O. Rorty [ed.] The Identities of Persons (1976; U. of California P.) Reprinted in his Philosophical Papers I.
  9. ^ Massimo Piattelli-Palmarini; Juan Uriagereka; Pello Salaburu (29 January 2009). Of Minds and Language: A Dialogue with Noam Chomsky in the Basque Country. Oxford University Press. pp. 382–. ISBN 978-0-19-156260-0.
  10. ^ Noam Chomsky (2010). Chomsky Notebook. Columbia University Press. pp. 9–. ISBN 978-0-231-14475-9.
  11. ^ James McGilvray (25 November 2013). Chomsky: Language, Mind and Politics. Polity. pp. 72–. ISBN 978-0-7456-4990-0.
  12. ^ Steve Grand (2003). Creation: Life and how to make it. Harvard.
  13. ^ Dave Ward, David Silverman and Mario Villalobos (18 April 2017). Introduction: Varieties of Enactivism. Springer.
  14. ^
  15. ^ Oberhaus, Daniel (12 December 2020). "The Oldest Crewed Deep Sea Submarine Just Got a Big Makeover". Wired.
  16. ^ Hud, Nicholas V.; Cafferty, Brian J.; Krishnamurthy, Ramanarayanan; William, Loren Dean (18 April 2013). "The origin of RNA and "my grandfather's axe"". Chemistry & Biology. 20 (4): 466. doi:10.1016/j.chembiol.2013.03.012. PMID 23601635.
  17. ^ Hosey, Lance (9 October 2018). "The Ship of Theseus: Identity and the Barcelona Pavilion(s)". Journal of Architectural Education. 72 (2): 230–247.

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