Ship of TheseusThe story of the Ship of Theseus is meant to highlight some basic problems regarding the identity of objects and their persistence through time. The story dates back to the ancient Greeks and has been told in a variety of ways in order to make various points.
Story 1:
There once was a ship whose captain was named Theseus. This ship was made of a large number of parts. One day (we’ll call this day D1) Theseus and his crew set out on a long voyage. On D1, the Ship of Theseus consisted of a determinate set of physical parts. As the voyage moved along, the crew recognized that they would occasionally have to make repairs to the ship, sometimes throwing old planks overboard and replacing them with new planks. After a long while, on Day 3002, it turns out the crew had replaced every part of the ship and there were no longer any original parts left. The question that naturally arises here is whether the Ship of Theseus on Day 3002 is the same ship as the Ship of Theseus on Day 1, even though they share none of the same physical parts.
Story 2:
Now suppose that, unbeknownst to Theseus and his crew, there had been a man collecting all the old parts of the original Ship of Theseus (the ship as it was on Day 1). Let us further suppose that on Day 3002, when he collects the final discarded part, he completely rebuilds the ship with nothing but the original parts. Now, we find ourselves with two candidates for the Ship of Theseus. Which one, if either, is the actual Ship of Theseus?
The Ship of Theseus story raises several issues for our concept identity. Intuitively, we may be inclined to say that the Ship of Theseus is identical to the collection of its parts. However, this seems too extreme, because the collection of parts change even when we merely replace a single plank. Similarly, if the Ship of Theseus were to have suddenly exploded and been annihilated, there is a sense in which all of its parts would still persist yet we would not say that the ship persists. Perhaps the ship is identical not only with the combination of its but also with the specific configuration of its parts (i.e. its structure). But this still leaves us with a problem: we are not inclined to say that an object becomes a completely different object when the it goes through small changes, but we are inclined to say that it ceases to be the same object when it goes through radical change. If the Ship of Theseus story makes anything clear it is this: that any acceptable theory of identity is going to have to wrestle with the problem of change over time.
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