In Ancient Greek philosophy, The Ship of Theseus is a thought experiment that asks whether an entity that has had all of its original components replaced remains the same entity. It has applications to the philosophical study of identity, and has inspired a variety of proposed solutions in contemporary philosophy of mind.
History
The "Ship of Theseus" was first introduced in Greek legend as reported by the historian, biographer, and essayist Plutarch[1]:
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, Life of Theseus[1]
Plutarch thus questions whether the ship would remain the same if it were entirely replaced, piece by piece. Centuries later, the philosopher Thomas Hobbes[2] 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]
Several variants are known, including the grandfather's axe and Trigger’s broom, where an old broom or axe has had both its head and its handle replaced, leaving no original components.[citation needed]
An ancient Buddhist text titled in Sanskrit Mahāprajñāpāramitopadeśa, which was later translated into Classical Chinese (Da zhidu lun 大智度論), contains a similar philosophical puzzle. It takes the form of a body-swapping story. The story tells of a traveler who encountered two demons in the night. As one demon ripped off all parts of the traveler's body one by one, the other demon replaced them with those of a corpse. The traveler was left confused about who he was after the body-swapping.[4]
Proposed resolutions
Four-dimensionalism
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.[5]
Cognitive science
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.[6] Chomsky says that this is not an unassailable assumption, from the perspective of the natural sciences, because human intuition is often mistaken.[7] 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.[8]
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.[9] When Theseus thinks of his ship, he has expectations about what parts 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[10] 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 reassembles 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.
See also
References
- ^ a b Plutarch. "Life of Theseus (23.1)". The Internet Classics Archive. Retrieved 2008-07-15.
- ^ De Corpore, ch 11.7
- ^ Cohen, S. Marc (2004). "Identity, Persistence, and the Ship of Theseus". faculty.washington.edu. Retrieved 2019-03-15.
- ^ 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. 29 (5): 739–762. doi:10.1080/09608788.2021.1881881. S2CID 233821050. An ungated version is available here or here.
- ^ 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.
- ^ 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.
- ^ Noam Chomsky (2010). Chomsky Notebook. Columbia University Press. pp. 9–. ISBN 978-0-231-14475-9.
- ^ James McGilvray (25 November 2013). Chomsky: Language, Mind and Politics. Polity. pp. 72–. ISBN 978-0-7456-4990-0.
- ^ Steve Grand (2003). Creation: Life and how to make it. Harvard.
- ^ Dave Ward, David Silverman and Mario Villalobos (18 April 2017). "Introduction: Varieties of Enactivism". Topoi. Springer. 36 (3): 365–375. doi:10.1007/s11245-017-9484-6. hdl:20.500.11820/cd543eb4-2ac5-4521-94eb-c39c43295840. S2CID 171748138.