Slide 1
A ship keeps changing
The Ship of Theseus puzzle asks whether an object remains the same when its parts are gradually replaced. Ordinary repair opens a problem about identity.
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Numerical identity means being one and the same object, rather than merely resembling it. Two newly built ships could look exactly alike while remaining two ships, so similarity cannot settle the puzzle by itself.
Slide 2
Continuity seems to matter
Replacing one plank usually counts as repairing a ship. Repeating that operation makes it hard to identify a single change that creates a different ship.
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Imagine keeping the vessel in service throughout the repairs. Its route, crew and ownership records continue. These continuities support ordinary identification, although none automatically proves a complete philosophical theory of persistence.
Slide 3
The discarded planks return
Now imagine assembling the original planks into another ship. Material continuity and continuity of use seem to point toward different candidates.
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The thought experiment is difficult because both candidates have a plausible connection with the earlier vessel. Calling both numerically identical to it would, under ordinary identity logic, also make them identical to each other.
Slide 4
Choose a criterion carefully
Proposed answers emphasize matter, form, continuity or parts extended through time. Each approach must explain more than one carefully chosen example.
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A criterion that suits a ship may work poorly for a living organism whose materials continually change. Philosophers therefore ask whether persistence depends on the kind of thing under discussion.
Slide 5
Practical labels do another job
A museum or registry can adopt a workable rule for naming the ship. That convention need not resolve every metaphysical question.
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An insurance policy may identify the repaired vessel through a registration number. The rule can serve its institutional purpose even while the puzzle about material replacement remains open to philosophical disagreement.
Sources
- Identity Over Time
Stanford Encyclopedia of Philosophy