Experiment #3 · Thought experiment

The Ship of Theseus

Identity through change

Plutarch (transmitting an older Athenian puzzle) · c. 75 AD · Metaphysics of identity

First published: Plutarch, *Life of Theseus*, ch. 23.

If every plank is replaced one by one, is it still the same ship? And if you rebuild the original out of the discarded planks — which one is?

The ship in which Theseus returned from Crete was preserved at Athens; its rotting planks were replaced one at a time over centuries. The Athenian philosophers asked whether the ship at the end was the same ship. Thomas Hobbes added the second horn (*De Corpore*, 1655): suppose someone collects every discarded plank and rebuilds the original. Now there are two candidates. The puzzle is the simplest possible stress-test for theories of persistence — for what it takes for a thing to be *the same thing* over time, and whether identity is intrinsic or relative to a sortal, a function, or an observer.

Formulation

Take ship S at time t0. Replace planks gradually until at time t1 no original plank remains; call this ship A. Meanwhile collect the discarded planks and reassemble them at t1; call this ship B. Each of (S = A), (S = B), (S = neither) leads to a recognisable theory of identity, and each contradicts the others.

Compare this experiment

Dimensions Engaged

◉

Matter

Targets Matter · Ontological Status: is "the ship" a substance (a single bearer of properties persisting through material change), or a *relational* / *emergent* pattern imposed on changing matter?

⧖

Time

Forces a choice on Time · Traversability and persistence: endurantism (the whole ship is wholly present at each time) vs perdurantism (only temporal parts exist; the ship is a four-dimensional worm). Each makes a different verdict on A vs B.

◎

Observer

Whether the ship's identity depends on observer-attributed sortals or functional roles (the courtroom ship, the museum ship, Theseus's ship) bears on Observer · Metaphysical Agency: does the world come pre-sorted, or is sorting our doing?

Responses — How Schools Engage

Affirms / takes the bait 3

Hylomorphism

Aristotle/Aquinas: the ship is matter informed by a substantial form. Form persists through material replacement so long as the function and structure are maintained — ship A is Theseus's ship; ship B is a replica.

Realism

Common-sense realism: the gradually-repaired ship is the same ship because that is what everyone has always meant by "the same ship." The reassembled hulk is, at best, a reconstruction.

Structuralism

Identity supervenes on structural role, not material constitution. Whichever ship continues to occupy the structural position of "Theseus's ship" in the historical network is the ship — typically A.

Reframes the question 4

Process Philosophy

The puzzle assumes substance metaphysics that processes do not need. "The ship" is a pattern of becoming; asking which of A or B "is" the original mistakes a temporal flow for a thing.

Buddhism

Anatta and impermanence dissolve the question: neither A nor B is *the* ship because there was no enduring self-natured ship to begin with — only momentary aggregates and the names we hang on them.

Analytic Metaphysics / Logical Atomism

Four-dimensionalism (Lewis, Sider): A and B are distinct space-time worms that share an early temporal segment. Each is "Theseus's ship" relative to a different counting principle; there is no further fact-of-the-matter.

Pragmatism

Which one *is* the ship depends on what we want to do with the answer (insurance, museum exhibit, commemoration). Identity claims are tools, not discoveries; the puzzle has different correct answers for different practical purposes.